doi.org/10.26434/chemrxiv.12128292.v1

Self-Adjusting Binding Pockets Enhance H₂ and CH₄ Adsorption in aUranium-Based Metal–Organic FrameworkDominik P. Halter, Ryan A. Klein, Michael A. Boreen, Benjamin A. Trump, Craig M. Brown, Jeffrey R. Long

Submitted date: 15/04/2020 • Posted date: 17/04/2020Licence: CC BY-NC-ND 4.0Citation information: Halter, Dominik P.; Klein, Ryan A.; Boreen, Michael A.; Trump, Benjamin A.; Brown,Craig M.; Long, Jeffrey R. (2020): Self-Adjusting Binding Pockets Enhance H₂ and CH₄ Adsorption in aUranium-Based Metal–Organic Framework. ChemRxiv. Preprint.https://doi.org/10.26434/chemrxiv.12128292.v1

A new, air-stable, permanently porous uranium(IV) metal–organic framework U(bdc)2 (1, bdc2− =1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Lowtemperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures.In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example ofcooperative framework contraction (ΔV = −7.8%), triggered by D2 adsorption at low pressures. Thisdeformation creates two optimized binding pockets for hydrogen (Qst = −8.6 kJ/mol) per pore, in agreementwith H2 adsorption data. Analogous experiments with CD4 (Qst = −24.8 kJ/mol) and N,N-dimethylformamideas guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique foreach adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategiccombination of binding pockets and structural flexibility in metal–organic frameworks holds great potential forthe development of new adsorbents with an enhanced substrate affinity.

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Self-Adjusting Binding Pockets Enhance H2 and CH4 Adsorption

in a Uranium-Based Metal–Organic Framework

Dominik P. Halter,[a,b] Ryan A. Klein,[c,d] Michael A. Boreen,[a,e] Benjamin A. Trump,[d] Craig M. Brown,[d,f]

and Jeffrey R. Long*[a,b,g]

Abstract: A new, air-stable, permanently porous uranium(IV)

metal–organic framework U(bdc)2 (1, bdc2− = 1,4-benzene-

dicarboxylate) was synthesized and its H2 and CH4 adsorption

properties were investigated. Low temperature adsorption

isotherms confirm strong adsorption of both gases in the

framework at low pressures. In situ gas-dosed neutron diffraction

experiments with different D2 loadings revealed a rare example of cooperative framework contraction (ΔV = −7.8%), triggered by D2

adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen (Qst = −8.6 kJ/mol) per pore, in agreement

with H2 adsorption data. Analogous experiments with CD4 (Qst = −24.8 kJ/mol) and N,N-dimethylformamide as guests revealed that the

binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest

interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal–organic frameworks holds

great potential for the development of new adsorbents with an enhanced substrate affinity.

Introduction

Metal–organic frameworks are a class of chemically-robust, porous, and often rigid materials, composed of metal ions or clusters connected by bridging organic linkers.[1] The physical and chemical properties of these materials are highly tunable based on choice of metal and linker, and thus metal–organic frameworks have been proposed for a wealth of applications,[2] including catalysis,[3] sensing,[4] carbon capture,[5] gas

separations,[6] and gas storage.[7] Metal–organic frameworks have attracted particular interest as candidate gas storage materials for H2 and CH4 that could enable more efficient use of these energy carriers as cleaner fuel alternatives.[8,9–11] However, significant advances are still needed to develop frameworks capable of maintaining interactions with these guests at ambient temperatures.[12,13]

Two main strategies have been developed to achieve strong binding of H2 and CH4 in metal–organic frameworks. The first approach utilizes materials with coordinatively-unsaturated metal sites, which can polarize and strongly bind various guests.[14] Representative of this materials class is the framework Ni2(m-dobdc) (m-dobdc4− = 4,6-dioxido-1,3-benzenedicarboxylate), which is currently the top performing material for ambient temperature, physisorptive H2 storage.[9,10] The other strategy exploits tight binding pockets in small-pore frameworks, which can engage in multiple, weak interactions with guest molecules to achieve strong overall guest binding, analogous to shape-selective molecular recognition in enzymes.[15] An example of how such cumulative dispersion forces can outperform strong interactions at open metal sites is the adsorption of CH4 in Cu2(btc)3 (HKUST-1, btc3− = 1,3,5-benzenetricarboxylate).[16] This material exhibits open metal sites and binding pockets in direct competition for CH4 adsorption. Structural characterization of Cu2(btc)3 dosed with low pressures of CD4 confirmed that methane preferably adsorbs at the binding pockets inside small octahedral cages of the framework, rather than through direct interactions at the copper(II) open metal sites. The reason for this behavior is that the multiple interactions inside the pore give rise to a higher overall binding energy than that achieved with a CH4 molecule adsorbed at a single copper(II) center (−21.8 versus −9.4 kJ/mol, respectively).[16]

Cumulative dispersion interactions between guest molecules and framework pockets decrease exponentially with the adsorbate–framework distances (F ∝ 1/r6), and therefore require a precise geometric fit between guest and binding pocket.[17] For

[a] Dr. D. P. Halter, M. A. Boreen, Prof. Dr. J. R. Long

Department of Chemistry, University of California, Berkeley Berkeley, CA 94720 (USA) E-mail: jrlong@berkeley.edu

[b] Dr. D. P. Halter, Prof. J. R. Long

Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley, CA 94720 (USA)

[c] Dr. R. A. Klein

Chemistry and Nanoscience Department National Renewable Energy Laboratory Golden, CO 80401 (USA)

[d] Dr. R. A. Klein, Dr. B. A. Trump, Prof. Dr. C. M. Brown

Center for Neutron Research National Institute of Standards and Technology Gaithersburg, MD 20899 (USA)

[e] M. A. Boreen

Chemical Sciences Division Lawrence Berkeley National Laboratory Berkeley, CA 94720 (USA)

[f] Prof. Dr. C. M. Brown

Department of Chemical Engineering University of Delaware Newark, DE 19716 (USA)

[g] Prof. Dr. J. R. Long

Department of Chemical and Biomolecular Engineering, University of California, Berkeley Berkeley, CA 94720 (USA)

Two pockets per pore: Shrink to fit!

U(bdc)2

D2

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example, as a result of its smaller kinetic diameter relative to CH4,[18] H2 preferentially binds at the open metal sites of Cu2(btc)3, rather than in the hexagonal pockets.[19] The development of new frameworks with efficient binding pockets therefore requires precise optimization for each adsorbate of interest, although achieving this goal by design remains a significant challenge.

An alternative approach to circumvent the synthetic intricacy of developing materials with optimized guest-specific binding pockets, are materials that combine small binding pockets with moderate framework flexibility.[20] Synthetic tuning can thus be used to design crude binding pockets, which are capable of self-adjusting in response to guest adsorption. Together, these design features could enable access to optimal binding pocket geometries for a variety of guests within the same material.

Flexibility is typically introduced into metal–organic frameworks by utilizing organic linkers with non-rigid stems, by interconnecting metals with non-chelating linkers, or by cross-linking two-dimensional frameworks with additional ditopic but weakly binding linkers.[21,22] Prominent examples are M(OH)(bdc) (MIL–53; bdc2− = 1,4-benzenedicarboxylate; M = Fe, Cr, Sc, Al, or Ga)[23,24,25] and M3(O)(OH)(H2O)2(bdc)3 (MIL–88; M = Fe, Cr).[26] These frameworks undergo drastic geometric distortions upon guest adsorption, often referred to as framework swelling, which can induce a substantial unit cell volume increase of up to 74%, as shown for example by CO2 adsorption in Fe(OH)(bdc).[27] Such large structural changes are too extreme to drive the subtle binding pocket adjustments sought here. One could instead envision limiting the flexibility of non-chelating bdc2− linkers by substantially increasing the number of metal-ligand bonds per metal node. A higher coordination number should limit structural rearrangements by causing steric encumbrance around the metal nodes and increase rigidity by further crosslinking the resulting material. Additionally, a higher ligand-to-metal ratio could result in smaller pore sizes and better binding pockets.

With their tendency to adopt high coordination numbers, actinides are well suited as metal nodes for the development of such materials.[28] We chose depleted uranium to test our hypothesis, as it is only mildly radioactive and because a limited but growing number of uranium-based frameworks have already been reported and could guide the synthesis.[29] Inspired by previous work on the synthesis of porous metal–organic frameworks from uranium(IV) and bdc2− linkers,[30] we synthesized a new, three-dimensional U(bdc)2 phase (1) with permanent porosity and a moderate level of structural flexibility. Using a combination of gas adsorption studies and in situ powder neutron diffraction experiments, we demonstrate that this framework undergoes an adjustable contraction of its pores to accommodate and strongly bind H2 and CH4, with different levels of contraction and host–guest interactions for each molecule.

Results and Discussion

The compound U(bdc)2·4H2O (1–H2O) was synthesized through the reaction of UI4(1,4-dioxane)2 with H2bdc in N,N-dimethylformamide (DMF, < 0.15 % water content as received) at 140 °C under argon inside a Parr autoclave. After three days, the material was isolated in 79% yield as air-stable, thin emerald green needle-shaped crystals. Single crystal X-ray diffraction analysis was used to determine the structure of

1–H2O (Figure 1), and selected bond distances and angles are given in Table S5 of the Supporting Information. We note that powder X-ray diffraction patterns collected for bulk samples of 1–H2O match the simulated pattern determined from single-crystal data, confirming the bulk purity of the crystalline material (Figure S7).

Compound 1–H2O crystallizes in the space group C2/c and features eight-coordinate uranium centers in a distorted square-antiprismatic environment. Each uranium(IV) is coordinated to one oxygen atom of eight different bdc2− linkers, and all linkers are coordinated to four different uranium ions in a bridging fashion. This motif results in an overall framework structure consisting of distorted parallelepipedal pores (Figure 1a) formed by chains of uranium(IV) centers that propagate along the crystallographic c-axis (Figure S17) and are bridged by bdc2− linkers bent in a concave and convex fashion. Each pore is formed by two opposing, inwardly bent bdc2− linkers at the sides and is capped at the top and bottom by a bowl-shaped arrangement of three additional bdc2− linkers (Figure 1b,c). The resulting geometry yields two identical binding pockets per pore that are ~5 Å in diameter and related by an inversion center.

In the as-synthesized framework, each binding pocket is occupied by two disordered water molecules, yielding the composition U(bdc)2·4H2O, which was also confirmed by thermogravimetric analysis (Figure S6). While disorder precluded modeling of any specific interactions, the guest water molecules are likely to engage in hydrogen bonding with each other and with the highly polarized U–O bonds. We note that the structure of the pores is such that guests could engage in a

Figure 1. (a) Single crystal X-ray diffraction structure of 1–H2O viewed along the c axis, showing the parallelepipedal pores. (b) Truncated structure showing one of the pores of 1–H2O along the crystallographic c-axis, with the two identical binding pockets of the pore depicted as blue spheres. (c) The same view as in (b), rotated by 90° to visualize the bowl-shaped arrangement of three bdc2− linkers that form the cap of each binding pocket. Orange, red, and grey spheres represent U, O, and C atoms, respectively; solvent and H atoms are omitted for clarity.

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variety of additional interactions, including with the linker -systems and arene C–H bonds.

Activated U(bdc)2 (1) was obtained by heating 1–H2O at 260 °C for 10 h under dynamic vacuum. Combustion analysis confirmed the empirical formula for 1 and the removal of guest water molecules. Nitrogen adsorption isotherms obtained at 77 K for four different samples revealed the activated material is permanently porous, with an average Langmuir surface area of 497 ± 6 m²/g (Figure S1). Powder X-ray diffraction analysis confirmed that that 1 remains crystalline with a slightly different structure from that of its solvated analogue (see Supporting Information, Figure S7). Interestingly, while many flexible frameworks contract or even fully collapse to a nonporous structure upon solvent removal,[11,31] activation of 1–H2O to give 1 results in an expansion of the framework along the crystallographic b-axis, from 12.598(1) to 12.812(1) Å. This change results in an increase in the unit cell volume from 1887.4(3) to 1902.1(2) Å3, while retaining the C2/c space group. This behavior upon guest removal indicates that the framework binding pockets are indeed able to contract to improve interactions with adsorbates.

We sought to study the flexibility of 1 in more detail using H2 and CH4 as probe molecules (with kinetic diameters of 2.9 and 3.8 Å, respectively)[18] of interest for potential gas storage applications. The low-pressure H2 adsorption isotherm for U(bdc)2 at 77 K exhibits an initial steep rise to ~3.5 mmol/g at 115 mbar, which is indicative of the presence of strong adsorption sites (Figure 2). We note that this loading corresponds to the theoretical capacity expected for adsorption of one H2 molecule per adsorption pocket (two per pore). With further increasing pressure, the quantity of adsorbed H2 increases very gradually to an apparent saturation value of ~4.9 mmol/g at 1.2 mbar. A dual site Langmuir model was used to fit independently H2 adsorption data collected at 77 and 87 K (see Section 3 of the Supporting Information, Figure S2, and Table S1), and the Clausius–Clapeyron equation was then employed to calculate the isosteric heat (Qst) of H2 adsorption as a function of loading (Figure 2, inset). For loadings up to 2.5 mmol/g, H2 adsorbs exclusively at primary binding sites in the framework pockets (see below) to give a Qst of −8.6 kJ/mol. Notably, this value is larger in magnitude than the H2 isosteric heat of adsorption in activated carbon materials (–5.0 to –6.4 kJ/mol)[32] and the majority of frameworks with coordinatively-saturated metal sites (−4.1 to −8.8 kJ/mol).[33]

The CH4 adsorption isotherm for 1 obtained at 195 K exhibits a steep uptake similar to that characterized for H2 at low pressures, again indicative of strong interactions between CH4 and the binding pockets of the framework (Figure 3). A dual site Langmuir model was used to simultaneously fit isotherm data collected at 195, 273, 298, and 308 K, and the Clausius−Clapeyron equation was then employed to calculate a value of Qst = −24.8 kJ/mol at low loadings (Figure S5). Notably, this value surpasses that determined for Zn4O(bdc)3 (MOF-5; Qst = −12.3 kJ/mol) and even values for frameworks with snugly fitting pore window, such as Cu2(btc)3 (Qst = −17.1 kJ/mol), or strongly polarizing open metal cation sites, as in Ni2(dobdc) (dobdc4− = 2,5-dioxido1,4-benzenedicarboxylate; Qst = −20.6 kJ/mol).[13,16]

It is clear that the binding pockets in U(bdc)2 can strongly interact with both H2 and CH4, despite their different sizes, which suggests that the framework may distort or flex to optimize interactions with different guest molecules. In order to study the framework–guest interactions in more detail, we turned to in situ gas-dosing powder neutron diffraction. The powder neutron diffraction pattern of activated 1 at 9 K was first collected as a reference for gas dosing experiments (see Supporting Information, Figure S9). Dosing with 0.3 equiv. of D2 per pore results in clear changes in the powder pattern, particularly visible at low values of scattering angle 2θ (Figures 4 and S10). Specifically, the reflections of 1 decrease in intensity while a second set of peaks arises, ascribed to a new crystalline phase 1–D2. Upon increasing the loading to 0.7 equiv. of D2, both phases are still present, although the peaks of 1 diminish further and the peaks of newly formed 1–D2 gain in intensity (Figures 4 and S11). The two phases coexist up to a loading of at least 1.5 equiv. D2 per pore (Figure S12), and their interconversion is best followed by evaluating the high intensity, low angle peaks at 2θ ≈ 11.85° for 1 and at 2θ ≈ 12.63° for 1–D2 in Figure 4. These data strongly suggest that cooperative effects drive an adsorbate-induced framework distortion from 1 to 1–D2. Such a mechanism is in contrast to a gradual and homogeneous uptake of D2, or a gradually changing degree of distortion depending on the D2-loading. As a result, before achieving saturation loading, some individual crystallites of the sample will be distorted, such that both binding pockets per pore are occupied with a D2 molecule, while others will remain in the activated structure of 1. At the highest D2 dosing level of 2.5 equiv. per pore, the

Figure 2. Hydrogen adsorption isotherm for 1, measured at 77 K. Inset: loading-dependent isosteric heat of adsorption (Qst) for H2 in 1.

Figure 3. Methane adsorption isotherms for 1 collected at the indicated temperatures.

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diffraction pattern of the sample contains only reflections associated with 1–D2. (see Supporting Information, Figure S13).

In situ powder neutron diffraction experiments were also carried out by dosing 1 with 0.7 and 1.5 equiv. of CD4 (Figures S14 and S15). The data from these experiments suggest a similar cooperative transformation from 1 to an adsorbed phase 1–CD4. Rietveld refinements were applied to all powder neutron diffraction data (see Section 6 in the Supporting Information) in order to elucidate adsorbate-induced structural deformations and characterize specific adsorption sites for D2 and CD4. Selected unit cell parameters determined for the different structures are summarized in Table 1. Based on unit cell volume, 1 contracts to a greater extent to accommodate D2 than it does in the presence of CH4.

Surprisingly, a structural comparison of 1 with 1–D2 and 1–CD4 reveals an almost constant coordination environment around the uranium nodes in each phase. The framework flexibility instead relies on a tilting of the parallelepipedal pores, which is clearly seen by comparing the pore geometries of 1 and 1–D2 dosed with 2.5 equiv. D2, as shown in Figure 5a. Here, each structure

is overlaid with an idealized parallelogram with corners defined by the uranium ions. Dosing with 2.5 equiv. of D2 results in a change of the idealized parallelogram angles, φ1 and φ2, from 77.1(1)° and 102.902(3)° in 1 to 65.03(6)° and 114.973(1)° in 1–D2. In order to accommodate this rearrangement, the two unique dihedral angles, ω1 and ω2, between the bdc2− O–C–O planes and the neighboring O–U···U–O planes adjust from 151(1)° and 168.4(9)° in 1 to 138.5(4)° and 174.9(5)° in 1–D2 (Figure 5b).

The resulting hinge-type bending between the UO8 nodes and linkers is analogous to the change that occurs in the structure of the flexible framework Cr(OH)(bdc) upon water adsorption.[21] In particular, water adsorption is accompanied by a unit cell volume decrease from 1486.1 to 1012.6 Å3, as well as a decrease of the symmetrical dihedral angles, ω,from 179.8° to 162.3°. The analogous idealized Cr···Cr···Cr angles φ1 and φ2 in Cr(OH)(bdc) change drastically from 75.9° and 104.2° (activated) to 44.8° and 135.2° (hydrated).[23] Interestingly, in distinct contrast to 1, Cr(OH)(bdc) distorts very little upon interaction with D2 (< 4 equiv. per pore), adopting a symmetric dihedral angle ω= 178.4° and Cr···Cr···Cr angles of 80.6° and 99.4°, concomitant with a very small unit cell volume increase to 1534.5 Å3.[25,34] The change in the structure of 1 upon dosing with 2.5 equiv. of D2 results in a much more drastic change in unit cell volume, from 1902.1(2) to 1754.5(2) Å3. We rationalize that the greater deformation of 1 arises as a result of its better ability to enshroud H2 within its pores, which leads to a greater adsorption enthalpy (Qst = −8.6 kJ/mol vs. −6.9 kJ/mol for Cr(OH)(bdc)),[35] and a larger driving force for structural rearrangement. Thus, the smaller pores within the framework of 1 are able to optimize binding through multiple stabilizing interactions, whereas the comparably large pores of Cr(OH)(bdc) provide fewer contacts.

In order to elucidate the hydrogen binding sites in 1, we treated the D2 molecules as “super atoms” in our analysis of the diffraction data (see Supporting Information, Section 6).[36,37] We first analyzed the structure of 1 loaded with 1.5 equiv. of D2 per pore (corresponding to less than one D2 per pocket) to enable an accurate structure determination in the absence of adsorbate–adsorbate interactions.[38] As expected, the D2 super atoms were located in both binding pockets of each pore, with an occupancy of 75% per site. Each D2 super atom is situated within van der Waals contact distance of three H atoms of bdc2−

Figure 4. Rietveld refinement fits of powder neutron diffraction patterns ( = 2.0772 Å, T = 9 K) collected for activated 1 and activated 1 dosed with 0.3, 0.7, and 1.5 equiv. of D2 per pore. Black (lower) and blue (upper) tick marks indicate calculated Bragg peak positions for 1 and the D2 adsorbed phase, 1–D2, respectively. Arrows indicate peaks that best illustrate the conversion of 1 to 1–D2 with increasing quantities of D2.

Table 1. Unit cell parameters (space group C2/c) for activated 1 and 1 dosed with different adsorbates, along with selected angles describing the pore deformation upon guest adsorption. Angles 1 and 2 describe the U···U···U angles of the idealized parallelogram spanned by the four corner uranium atoms within the crystallographic ab plane of each pore, as illustrated in Figure 5a. Angles 1 and 2 describe the dihedral angle between O–U···U–O planes and O–C–O planes at each end of a bdc2− linker, as illustrated in Figure 5b for 1 and 1–D2. One standard deviations for all values are given in parentheses.

Sample a (Å) b (Å) c (Å) V (Å3) φ1 (°) φ2 (°) ω1 (°) ω2 (°)

1 17.587(1) 12.812(1) 9.2999(5) 1902.1(2) 77.1(1) 102.902(3) 151(1) 168.4(9)

1–D2 (0.3 equiv.) 18.361(7) 11.35(1) 9.335(2) 1782(2) 67.51(1) 112.491(9) 148.7(3) 159.6(3)

1–D2 (0.7 equiv.) 18.402(3) 11.324(5) 9.333(1) 1781.4(8) 67.4(2) 112.576(1) 130(2) 175(3)

1–D2 (1.5 equiv.) 18.456(1) 11.233(1) 9.3508(4) 1775.8(2) 66.86(6) 113.143(1) 141.4(8) 170(1)

1–D2 (2.5 equiv.) 18.665(1) 10.9486(8) 9.3838(5) 1754.5(2) 65.03(6) 114.973(1) 138.5(4) 174.9(5)

1–CD4 (1.5 equiv.) 18.031(1) 11.9665(7) 9.3206(4) 1839.3(2) 71.52(5) 108.483(1) 142(3) 171.1(9)

1–DMF 18.2658(7) 12.0252(5) 9.3579(3) 1865.6(1) 71.63(4) 108.373(1) 166(11) 164(4)

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linkers, the π-system of the outer pocket-capping bdc2– linker, and two oxygen atoms of the UO8 coordination polyhedron (Figure 6a). The D2···H contact distances of 2.96(1), 2.98(1), and 3.15(2) Å indicate moderately strong van der Waals interactions.[37,39] The distance from D2 to the centroid of the nearest benzene ring is 3.45(1) Å, which is indicative of a modest D2···π interaction,[40] while the closest D2···O contact is 3.59(1) Å. In the structure of 1 dosed with 2.5 equiv. of D2, an additional D2 molecule was located in the center of the pore (site II, see Figure 5a). The D2 molecules at site II are stabilized by four symmetry equivalent D2···D2 interactions at a distance of 3.10(1) Å, as well as by weak C–H···D2 contacts with the linkers (3.31(3) and 3.55(1) Å). As discussed above, in order to accommodate these interactions, the pores of 1 contract significantly around the D2 molecules, decreasing the unit cell volume by as much as 7.8% and shrinking the binding pocket diameter from 5.0 to 3.6 Å (see Supporting Information, Section 6). The crucial role of this structural distortion is further exemplified by considering a hypothetical D2 super atom at the

fractional coordinates of site I in fully activated 1. In this environment, the D2···framework interactions are elongated beyond meaningful van der Waals contact distances (see Supporting Information, Section 6).

Rietveld refinement of in situ powder neutron diffraction data collected for 1 dosed with 1.5 equiv. of CD4 confirmed that the molecule occupies the same adsorption pocket as D2 (site I). Due to the larger size of CD4 relative to D2, a less pronounced contraction of the framework is sufficient to enable similar host-guest contacts. The unit cell volume of 1–CD4 contracts by 3.4% to 1839.3(2) Å3, resulting in a binding pocket diameter of 4.1 Å. Notably, the adsorbed CD4 molecules are well-ordered as a result of a large number of specific host–guest interactions (Figure 6b). The nearest D···arene distances are 2.740(9) Å (side wall of the pore) and 3.407(8) Å (outer linker of bowl-shaped cap). These relatively short distances are consistent with those determined previously from studies of methane adsorption on benzene (2.1–3.8 Å) and support the characterized orientation of CD4 inside the pore of U(bdc)2.[16,41] Additional D···H van der Waals contacts at 2.57(1), 2.69(2), and 2.81(2) Å stabilize and orient the adsorbed CD4 molecules within the binding pocket. Adsorbed CD4 further interacts with three O atoms of two independent UO8 nodes at distances of 3.10(2), 3.25(1), and 3.50(1) Å. Lastly, adsorbate–adsorbate interactions based on D···D contacts at 2.84(1), 3.10(1), and 3.20(1) Å stabilize CD4 inside each pore.[42] Together, the wealth of stabilizing contacts explains the competitively high heat of adsorption (Qst = −24.8 kJ/mol) for methane in U(bdc)2. It is worth noting that methane is also expected to occupy a second adsorption site at higher loadings, as seen for D2. This observation is supported by the CH4 adsorption data shown in Figure 3. Here, initial steep uptake is associated with saturation of the binding pockets of site I until a loading of 3.5 mmol/g. The onset of far more gradual CH4 uptake to 4.1 mmol/g at 1.2 mbar suggests additional methane adsorption at a second, weaker binding site.

Finally, we sought to study the distortion of 1 in the presence of an even larger guest molecule and prepared crystals of 1–DMF by soaking the framework in dry DMF (kinetic diameter of 5.5 Å).[43] The structure of 1–DMF was determined from Rietveld refinement of powder X-ray diffraction data obtained at 298 K (Figure S8). The framework indeed contracts to optimize interactions with DMF, but the unit cell volume decreases by only 1.9% (compared to 7.8% and 3.4% in the cases of 2.5 equiv. D2 and 1.5 equiv. CD4, respectively) and the pocket

Figure 6. (a) Neutron powder diffraction structure of D2 adsorbed at site I in 1–D2 after dosing 1 with 2.5 equiv. D2 per pore. (b) Neutron powder diffraction structure of CD4 adsorbed at site I in 1–CD4 after dosing 1 with 1.5 equiv. CD4 per pore. (c) Powder X-ray diffraction structure of DMF adsorbed inside the pore of U(bdc)2. For clarity, only selected Interactions of DMF with the framework are depicted. All framework–guest interactions are depicted as aquamarine colored dashed lines. For clarity in (a) and (b), the pore is truncated and cut in half diagonally, showing only one of the two adsorption pockets of the pore. Orange, red, grey, blue, aquamarine, and white spheres represent U, O, C, N, D, and H atoms, respectively.

Figure 5. (a) Illustration of pores in 1 and 1–D2 (dosed with 2.5 equiv D2 per pore). The pore contraction upon D2 dosing is highlighted by the colored blue and purple areas within the crystallographic ab plane. Tilting of the pores to facilitate contraction is illustrated by idealized parallelograms (dashed lines) with corners defined by uranium atoms. Adsorbed D2 molecules inside the pores of 1–D2 are represented as blue spheres for adsorption site I and as brown spheres for adsorption site II. Each D2 super atom at site II is shared between two neighboring pores, accordingly the two depicted site II super atoms together account for an occupancy of one D2 molecule per pore. (b) Comparison of the dihedral angles 1 as described in the text (2 is not shown, but is the corresponding angle at the other end of the linker), representing the main structural distortion undergone by 1 upon adsorption of D2. Orange, red, and grey spheres represent U, O, and C atoms, respectively.

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diameter decreases to only 4.2 Å. While two molecules of the smaller guests D2 and CD4 can simultaneously occupy the two binding pockets in each pore, the larger DMF molecule occupies the whole pore space, bridging both pockets (Figure 6c). As a result, DMF is stabilized by seven of the eight bdc2− linkers that form the surrounding pore. While precise contact distances are obscured by disorder of DMF over two positions in the structure, the general identity of host-guest interactions in 1–DMF is clear. In particular, DMF binds through eight H···H contacts, three C–H···π-interactions, three O···H contacts involving the carbonyl and arene C–H moieties, and interactions of two DMF C–H groups with O atoms of two UO8 nodes (all distances between 2 and 4 Å).

Conclusions

Porous adsorbents with small binding pockets can engage in strong, selective host–guest interactions, and are therefore of interest for applications including gas capture and storage. However, it remains a significant challenge to tune a binding pocket structure to optimize interactions with a specific target molecule. In this work, we show that combining moderate flexibility with small pores in the new flexible metal–organic framework U(bdc)2 (1) eliminates the need for precise tuning of pore geometry. Indeed, this material is capable of uniquely adjusting its pore and binding pocket geometry to optimize host–guest interactions in the presence of even very weakly adsorbing molecules, such as H2, CH4. Temperature-dependent H2 and CH4 adsorption isotherms yielded isosteric heats of adsorption of −8.6 and −24.8 kJ/mol for H2 and CH4, respectively, confirming comparatively strong interactions of 1 with both gases, despite their different sizes. In situ powder neutron diffraction experiments with D2 and CD4 revealed that cooperative effects drive a spontaneous adjustment of the binding pockets in 1 to generate multiple stabilizing interactions between each adsorbate and the framework, which are not achieved without pore contraction. Altogether, our results demonstrate the utility of frameworks featuring self-adjusting binding pockets that can flex in response to different guest molecules and suggest further exploration of such materials will be advantageous in the search for adsorbents with improved gas storage properties.

Acknowledgements

This work was supported by the Hydrogen Materials - Advanced Research Consortium (HyMARC), established as part of the Energy Materials Network under the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract DE-AC02-05CH11231. Powder X-ray diffraction data were collected on beamline 17-BM at the Advanced Photon Source at Argonne National Laboratory, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357. Single-crystal X-ray diffraction data were collected at the Advanced Light Source beamline 12.2.1 at Lawrence Berkeley National Laboratory. The Advanced Light Source (ALS) is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. DOE under Contract No. DE-AC02-05CH11231. D.P.H. thanks the Alexander von Humboldt foundation for a Feodor Lynen postdoctoral research fellowship. R.A.K. acknowledges research

support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract DE-AC36-08GO28308. We further thank Colin A. Gould for helpful discussions, Ari Turkiewicz for assistance with single-crystal X-ray diffraction, Henry Z. H. Jiang and Maria V. Paley for help with acquiring high resolution powder X-ray diffraction data, and Dr. Katie R. Meihaus for editorial assistance.

Keywords: flexible MOF • gas storage • metal–organic frameworks • self-adjusting adsorption pocket • uranium

References

[1] a) H. Furukawa, K. E. Cordova, M. O'Keeffe, O. M. Yaghi, Science 2013, 341, 1230444; b) N. Stock, S. Biswas, Chem. Rev. 2012, 112, 933; c) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O'Keeffe, O. M. Yaghi, Science 2002, 295, 469; d) S. Yuan, L. Feng, K. Wang, J. Pang, M. Bosch, C. Lollar, Y. Sun, J. Qin, X. Yang, P. Zhang, Q. Wang, L. Zou, Y. Zhang, L. Zhang, Y. Fang, J. Li, H.-C. Zhou, Adv. Mater. 2018, 30, 1704303.

[2] a) T. Islamoglu, S. Goswami, Z. Li, A. J. Howarth, O. K. Farha, J. T. Hupp, Acc. Chem. Res. 2017, 50, 805; b) W. Lu, Z. Wei, Z.-Y. Gu, T.-F. Liu, J. Park, J. Park, J. Tian, M. Zhang, Q. Zhang, T. Gentle, M. Bosch, H.-C. Zhou, Chem. Soc. Rev. 2014, 43, 5561; c) A. U. Czaja, N. Trukhan, U. Müller, Chem. Soc. Rev. 2009, 38, 1284; d) C. H. Hendon, A. J. Rieth, M. D. Korzyński, M. Dincă, ACS Cent. Sci. 2017, 3, 554; e) A. Bétard, R. A. Fischer, Chem. Rev. 2012, 112, 1055.

[3] a) Q. Wang, D. Astruc, Chem. Rev. 2020, 120, 1438; b) D. J. Xiao, E. D. Bloch, J. A. Mason, W. L. Queen, M. R. Hudson, N. Planas, J. Borycz, A. L. Dzubak, P. Verma, K. Lee et al.J. R. Long, Nat. Chem. 2014, 6, 590; c) S. A. Burgess, A. Kassie, S. A. Baranowski, K. J. Fritzsching, K. Schmidt-Rohr, C. M. Brown, C. R. Wade, J. Am. Chem. Soc. 2016, 138, 1780; d) S. M. Cohen, Z. Zhang, J. A. Boissonnault, Inorg. Chem. 2016, 55, 7281; e) Y.-B. Huang, J. Liang, X.-S. Wang, R. Cao, Chem. Soc. Rev. 2017, 46, 126; f) J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen, J. T. Hupp, Chem. Soc. Rev. 2009, 38, 1450.

[4] a) L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. van Duyne, J. T. Hupp, Chem. Rev. 2012, 112, 1105; b) M. G. Campbell, D. Sheberla, S. F. Liu, T. M. Swager, M. Dincă, Angew. Chem. Int. Ed. 2015, 54, 4349; c) I. Stassen, N. Burtch, A. Talin, P. Falcaro, M. Allendorf, R. Ameloot, Chem. Soc. Rev. 2017, 46, 3185.

[5] a) K. Sumida, D. L. Rogow, J. A. Mason, T. M. McDonald, E. D. Bloch, Z. R. Herm, T.-H. Bae, J. R. Long, Chem. Rev. 2012, 112, 724; b) T. M. McDonald, J. A. Mason, X. Kong, E. D. Bloch, D. Gygi, A. Dani, V. Crocellà, F. Giordanino, S. O. Odoh, W. S. Drisdell et al.J. R. Long, Nature 2015, 519, 303; c) R. L. Siegelman, P. J. Milner, A. C. Forse, J.-H. Lee, K. A. Colwell, J. B. Neaton, J. A. Reimer, S. C. Weston, J. R. Long, J. Am. Chem. Soc. 2019, 141, 13171; d) M. Ding, R. W. Flaig, H.-L. Jiang, O. M. Yaghi, Chem. Soc. Rev. 2019, 48, 2783; e) D. J. Babu, G. He, J. Hao, M. T. Vahdat, P. A. Schouwink, M. Mensi, K. V. Agrawal, Adv. Mater. 2019, 31, 1900855.

[6] a) B. R. Barnett, M. I. Gonzalez, J. R. Long, Trends Chem. 2019, 1, 159; b) H. Li, K. Wang, Y. Sun, C. T. Lollar, J. Li, H.-C. Zhou, Mater. Today 2018, 21, 108; c) D. E. Jaramillo, D. A. Reed, H. Z. H. Jiang, J. Oktawiec, M. W. Mara, A. C. Forse, D. J. Lussier, R. A. Murphy, M. Cunningham, V. Colombo, D. K. Shuh, J. A. Reimer, J. R. Long, Nat. Mater. 2020, DOI: 10.1038/s41563-019-0597-8.

[7] a) B. Li, H.-M. Wen, W. Zhou, B. Chen, J. Phys. Chem. Lett. 2014, 5, 3468; b) R. E. Morris, P. S. Wheatley, Angew. Chem. Int. Ed. 2008, 47, 4966; c) D. A. Reed, D. J. Xiao, H. Z. H. Jiang, K. Chakarawet, J. Oktawiec, J. R. Long, Chem. Sci. 2020, 11, 1698; d) S. Ma, H.-C. Zhou, Chem. Commun. 2010, 46, 44; e) I. Senkovska, E. Barea, J. A. R. Navarro, S. Kaskel, Microporous Mesoporous Mat. 2012, 156, 115.

[8] a) P. García-Holley, B. Schweitzer, T. Islamoglu, Y. Liu, L. Lin, S. Rodriguez, M. H. Weston, J. T. Hupp, D. A. Gómez-Gualdrón, T. Yildirim, O. K. Farha, ACS Energy Lett. 2018, 3, 748; b) A. Ahmed, S. Seth, J. Purewal, A. G. Wong-Foy, M. Veenstra, A. J. Matzger, D. J. Siegel, Nat. Commun. 2019, 10, 1568; c) Y. He, W. Zhou, G. Qian, B. Chen, Chem. Soc. Rev. 2014, 43, 5657; d) K. V. Kumar, K. Preuss, M.-M. Titirici, F. Rodríguez-Reinoso, Chem. Rev. 2017, 117, 1796.

[9] M. T. Kapelewski, S. J. Geier, M. R. Hudson, D. Stück, J. A. Mason, J. N. Nelson, D. J. Xiao, Z. Hulvey, E. Gilmour, S. A. FitzGerald, M. Head-Gordon, C. M. Brown, J. R. Long, J. Am. Chem. Soc. 2014, 136, 12119.

[10] M. T. Kapelewski, T. Runčevski, J. D. Tarver, H. Z. H. Jiang, K. E. Hurst, P. A. Parilla, A. Ayala, T. Gennett, S. A. FitzGerald, C. M. Brown, J. R. Long, Chem. Mater. 2018, 30, 8179.

[11] J. A. Mason, J. Oktawiec, M. K. Taylor, M. R. Hudson, J. Rodriguez, J. E. Bachman, M. I. Gonzalez, A. Cervellino, A. Guagliardi, C. M. Brown, P. L. Llewellyn, N. Masciocchi, J. R. Long, Nature 2015, 527, 357.

7

[12] a) M. D. Allendorf, Z. Hulvey, T. Gennett, A. Ahmed, T. Autrey, J. Camp, E. Seon Cho, H. Furukawa, M. Haranczyk, M. Head-Gordon et al.B. C. Wood, Energy Environ. Sci. 2018, 11, 2784; b) M. P. Suh, H. J. Park, T. K. Prasad, D.-W. Lim, Chem. Rev. 2012, 112, 782.

[13] J. A. Mason, M. Veenstra, J. R. Long, Chem. Sci. 2014, 5, 32. [14] a) M. I. Gonzalez, J. A. Mason, E. D. Bloch, S. J. Teat, K. J. Gagnon, G.

Y. Morrison, W. L. Queen, J. R. Long, Chem. Sci. 2017, 8, 4387; b) D. Denysenko, M. Grzywa, J. Jelic, K. Reuter, D. Volkmer, Angew. Chem. Int. Ed. 2014, 53, 5832.

[15] P. G. Boyd, A. Chidambaram, E. García-Díez, C. P. Ireland, T. D. Daff, R. Bounds, A. Gładysiak, P. Schouwink, S. M. Moosavi, M. M. Maroto-Valer, J. A. Reimer, J. A. R. Navarro, T. K. Woo, S. Garcia, K. C. Stylianou, B. Smit, Nature 2019, 576, 253.

[16] Z. Hulvey, B. Vlaisavljevich, J. A. Mason, E. Tsivion, T. P. Dougherty, E. D. Bloch, M. Head-Gordon, B. Smit, J. R. Long, C. M. Brown, J. Am. Chem. Soc. 2015, 137, 10816.

[17] D. G. Truhlar, J. Chem. Educ. 2019, 96, 1671. [18] N. Mehio, S. Dai, D.-e. Jiang, J. Phys. Chem. A 2014, 118, 1150. [19] Y. Liu, C. M. Brown, D. A. Neumann, V. K. Peterson, C. J. Kepert, J.

Alloys Compd. 2007, 446-447, 385. [20] A. P. Katsoulidis, D. Antypov, G. F. S. Whitehead, E. J. Carrington, D. J.

Adams, N. G. Berry, G. R. Darling, M. S. Dyer, M. J. Rosseinsky, Nature 2019, 565, 213.

[21] A. Schneemann, V. Bon, I. Schwedler, I. Senkovska, S. Kaskel, R. A. Fischer, Chem. Soc. Rev. 2014, 43, 6062.

[22] a) L. Sarkisov, R. L. Martin, M. Haranczyk, B. Smit, J. Am. Chem. Soc. 2014, 136, 2228; b) J.-P. Zhang, H.-L. Zhou, D.-D. Zhou, P.-Q. Liao, X.-M. Chen, Nat. Sci. Rev. 2018, 5, 907.

[23] C. Serre, F. Millange, C. Thouvenot, M. Noguès, G. Marsolier, D. Louër, G. Férey, J. Am. Chem. Soc. 2002, 124, 13519.

[24] a) M. Vougo-Zanda, J. Huang, E. Anokhina, X. Wang, A. J. Jacobson, Inorg. Chem. 2008, 47, 11535; b) F. Millange, N. Guillou, M. E. Medina, G. Férey, A. Carlin-Sinclair, K. M. Golden, R. I. Walton, Chem. Mater. 2010, 22, 4237; c) J. P.S. Mowat, S. R. Miller, A. M.Z. Slawin, V. R. Seymour, S. E. Ashbrook, P. A. Wright, Microporous Mesoporous Mat. 2011, 142, 322.

[25] G. Férey, M. Latroche, C. Serre, F. Millange, T. Loiseau, A. Percheron-Guégan, Chem. Commun. 2003, 2976.

[26] S. Surblé, C. Serre, C. Mellot-Draznieks, F. Millange, G. Férey, Chem. Commun. 2006, 284.

[27] N. Guillou, S. Bourrelly, P. L. Llewellyn, R. I. Walton, F. Millange, CrystEngComm 2015, 17, 422.

[28] S. R. Daly, P. M. B. Piccoli, A. J. Schultz, T. K. Todorova, L. Gagliardi, G. S. Girolami, Angew. Chem. Int. Ed. 2010, 49, 3379.

[29] E. A. Dolgopolova, A. M. Rice, N. B. Shustova, Chem. Commun. 2018, 54, 6472.

[30] C. Falaise, A. Assen, I. Mihalcea, C. Volkringer, A. Mesbah, N. Dacheux, T. Loiseau, Dalton Trans. 2015, 44, 2639.

[31] a) V. Bon, I. Senkovska, D. Wallacher, D. M. Többens, I. Zizak, R. Feyerherm, U. Mueller, S. Kaskel, Inorg. Chem. 2014, 53, 1513; b) C. Mellot-Draznieks, C. Serre, S. Surblé, N. Audebrand, G. Férey, J. Am. Chem. Soc. 2005, 127, 16273; c) M. K. Taylor, T. Runčevski, J. Oktawiec, M. I. Gonzalez, R. L. Siegelman, J. A. Mason, J. Ye, C. M. Brown, J. R. Long, J. Am. Chem. Soc. 2016, 138, 15019.

[32] P. Bénard, R. Chahine, Langmuir 2001, 17, 1950. [33] L. J. Murray, M. Dincă, J. R. Long, Chem. Soc. Rev. 2009, 38, 1294. [34] F. M. Mulder, B. Assfour, J. Huot, T. J. Dingemans, M. Wagemaker, A.

J. Ramirez-Cuesta, J. Phys. Chem. C 2010, 114, 10648. [35] F. Salles, D. I. Kolokolov, H. Jobic, G. Maurin, P. L. Llewellyn, T. Devic,

C. Serre, G. Ferey, J. Phys. Chem. C 2009, 113, 7802. [36] R. A. Pollock, J.-H. Her, C. M. Brown, Y. Liu, A. Dailly, J. Phys. Chem.

C 2014, 118, 18197. [37] H. Wu, W. Zhou, T. Yildirim, J. Am. Chem. Soc. 2007, 129, 5314. [38] a) D. Gygi, E. D. Bloch, J. A. Mason, M. R. Hudson, M. I. Gonzalez, R.

L. Siegelman, T. A. Darwish, W. L. Queen, C. M. Brown, J. R. Long, Chem. Mater. 2016, 28, 1128; b) K. Sumida, J.-H. Her, M. Dincă, L. J. Murray, J. M. Schloss, C. J. Pierce, B. A. Thompson, S. A. FitzGerald, C. M. Brown, J. R. Long, J. Phys. Chem. C 2011, 115, 8414; c) T. Runčevski, M. T. Kapelewski, R. M. Torres-Gavosto, J. D. Tarver, C. M. Brown, J. R. Long, Chem. Commun. 2016, 52, 8251.

[39] a) J. Luo, H. Xu, Y. Liu, Y. Zhao, L. L. Daemen, C. Brown, T. V. Timofeeva, S. Ma, H.-C. Zhou, J. Am. Chem. Soc. 2008, 130, 9626; b) J. van Kranendonk, H. P. Gush, Phys. Lett. 1962, 1, 22.

[40] V. K. Peterson, Y. Liu, C. M. Brown, C. J. Kepert, J. Am. Chem. Soc. 2006, 128, 15578.

[41] a) S. Tsuzuki, K. Honda, T. Uchimaru, M. Mikami, K. Tanabe, J. Am. Chem. Soc. 2000, 122, 3746; b) A. L. Ringer, M. S. Figgs, M. O. Sinnokrot, C. D. Sherrill, J. Phys. Chem. A 2006, 110, 10822; c) H. Wu, W. Zhou, T. Yildirim, J. Phys. Chem. C 2009, 113, 3029.

[42] a) E. Tsivion, M. Head-Gordon, J. Phys. Chem. C 2017, 121, 12091; b) S. Tsuzuki, T. Uchimaru, K. Tanabe, Chem. Phys. Lett. 1998, 287, 202.

[43] J. E. ten Elshof, C. R. Abadal, J. Sekulić, S. R. Chowdhury, D. H. A. Blank, Microporous Mesoporous Mat. 2003, 65, 197.

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1

Supporting Information for:

Self-Adjusting Binding Pockets Enhance H2 and CH4 Adsorption

in a Uranium-Based Metal–Organic Framework

Dominik P. Halter, Ryan A. Klein, Michael A. Boreen, Benjamin A. Trump, Craig M. Brown, and Jeffrey

R. Long*

Abstract: A new, air-stable, permanently porous uranium(IV) metal–organic framework U(bdc)2 (1, bdc2− = 1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example of cooperative framework contraction (ΔV = −7.8%), triggered by D2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen (Qst = −8.6 kJ/mol) per pore, in agreement with H2 adsorption data. Analogous experiments with CD4 (Qst = −24.8 kJ/mol) and N,N-dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal–organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity.

*correspondence to: jrlong@berkeley.edu

Table of Contents

1. General experimental procedures ......................................................................................................................... 2

2. Synthesis of U(bdc)2 (1) ........................................................................................................................................ 3

3. Surface area determination and gas adsorption experiments .............................................................................. 4

4. Thermogravimetric analysis .................................................................................................................................. 7

5. Powder X-ray diffraction ........................................................................................................................................ 8

6. Powder neutron diffraction .................................................................................................................................... 9

7. Single crystal X-ray diffraction ............................................................................................................................. 14

8. References .......................................................................................................................................................... 17

2

1. General experimental procedures

General Procedures. The synthesis of U(bdc)2 (1) was performed under inert gas atmosphere using standard Schlenk line techniques and a glove box equipped with argon. Terephthalic acid was purchased from commercial vendors† and dried at 80 °C under reduced pressure (approx. 5 × 10−2 mbar) prior to use. N,N-Dimethylformamide (DMF) was purchased from Fischer Scientific (purity > 99.8 %, water content < 0.15 %) and degassed by sparging with argon prior to use. Anhydrous DMF was obtained by drying the degassed DMF over 4 Å activated molecular sieves. Anhydrous methanol was purchased from Sigma Millipore and used as received. UI4(1,4-dioxane)2 was synthesized according to the literature procedure.[1] Ultra-high purity grade (99.999% purity) helium, nitrogen, hydrogen, and methane were used for all adsorption measurements. Gas Adsorption Measurements. Gas adsorption data were obtained using instrumentation and protocols that closely follow a previously used approach,[2] and are reproduced here for completeness with new details relevant to this work. Gas adsorption isotherms for pressures in the range of 0 to 1.2 bar were measured using a Micromeritics ASAP 2020 or 2420 instrument. Activated samples were transferred under a N2 atmosphere to pre-weighed analysis tubes, which were capped with a TranSeal. Each sample was evacuated on the ASAP until the outgas rate was less than 3 μbar min−1. The evacuated analysis tube containing degassed sample was then carefully transferred to an electronic balance and weighed to determine the mass of sample (typically 100–150 mg). The tube was then fitted with an isothermal jacket and transferred back to the analysis port of the ASAP. The outgas rate was again confirmed to be less than 3 μ bar min−1. Langmuir surface areas were determined by measuring N2 adsorption isotherms in a 77 K liquid N2 bath and calculated using the Micromeritics software, assuming a value of 16.2 Å2 for the molecular cross-sectional area of N2. Elemental analysis was measured at the Microanalytical Facility at the College of Chemistry, University of California, Berkeley. Thermogravimetric Analysis (TGA) was performed TA Instruments TGA Q50 Thermogravimetric Analyzer at a ramp rate of 2 °C per minute under nitrogen flow. Laboratory powder X-ray diffraction. Patterns were collected using a Bruker AXS D8 Advance diffractometer using Cu Kα radiation (λ = 1.5418 Å). Synchrotron powder X-ray diffraction measurements. Synchrotron powder X-ray diffraction data for 1 and 1–DMF were collected on beamline 17-BMB at the Advanced Photon Source (APS) at Argonne National Laboratory (λ = 0.45246 Å). Samples were sealed in a quartz capillary, which was then sealed inside a Kapton tube with epoxy resin. Data was collected using an amorphous Si area detector with the two-dimensional patterns reduced to one-dimensional data with GSAS-II.[3] Measurements were conducted at room temperature (T ≈ 298 K), with samples hermetically sealed throughout the experiment. Powder neutron diffraction. Powder neutron diffraction experiments were performed at the National Institute of Standards and Technology Center for Neutron Research (NCNR) using the high-resolution neutron powder diffractometer, BT1. Data were collected using a Ge(311) monochromator with an in-pile 60' collimator, corresponding to a neutron wavelength of λ = 2.0772 Å. Specific experimental details are reported together with the data in the powder neutron diffraction section (Section 6). Single crystal X-ray diffraction. Diffraction data were obtained at the Advanced Light Source (ALS), Lawrence Berkeley National Lab, Berkeley, CA, station 12.2.1, using a silicon monochromated synchrotron radiation beam of 17 keV (λ = 0.7288 Å). Specific experimental details are reported together with the data in the single crystal X-ray diffraction section (Section 7).

† Certain commercial equipment, instruments, or materials are identified in this document. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the products identified are necessarily the best available for the purpose.

3

2. Synthesis of U(bdc)2 (1)

A glass vial was placed into an autoclave reactor (Parr Instrument Company, model 4749) and charged with UI4(1,4-dioxane)2 (242 mg, 0.263 mmol), terephthalic acid (130 mg, 0.79 mmol), and degassed, non-dried DMF (4.0 mL). The reaction mixture was briefly stirred with a spatula to dissolve all solids, before the vessel was sealed under argon and heated in an oven to 140 °C for 72 h. The crude product formed as emerald green needles, and a portion of the crystals were picked directly from the mother liquor for single-crystal X-ray diffraction analysis. The remaining crystals were transferred into a Schlenk flask, where the mother liquor was removed. Another portion of crystals were crushed and analyzed as a bulk sample using powder X-ray diffraction (see Figure S7). The remaining green solid was soaked four times in dry, degassed DMF (5 mL) at room temperature for 10 h each. A portion of this solid was used for powder X-ray diffraction characterization the DMF-loaded framework, as described in the main text. Then remaining DMF-soaked green, crystalline solid was isolated by decanting the solvent and then soaked four times in dry methanol (5 mL) at room temperature for 10 h each. After decanting the solvent, the product was dried in vacuo at 120 °C for 5 h. Finally, U(bdc)2 was activated by heating it to 260 °C under reduced pressure (2 × 10–6 bar) for 12 h, affording 1 as a green, microcrystalline powder in 79% yield (118 mg, 0.208 mmol). Elemental Analysis for U(bdc)2 (C16H8O8U): Calculated: C, 33.94; H, 1.42; N, 0.00. Found: C, 33.56; H, 1.38; N, 0.00. Note: In the absence of water, we found the reaction of UI4(1,4-dioxane)2 and H2(bdc) yields the reported two-dimensional phase U2(bdc)2(DMF)4.[4] This material was previously obtained from UCl4 under otherwise analogous conditions, indicating that H2O may have a structural directing effect during the synthesis of 1.

4

3. Surface area determination and gas adsorption experiments

In preparation for all gas adsorption measurements, U(bdc)2 samples were activated by heating the materials to 260 °C under dynamic vacuum until the outgas rate was less than 3 μbar min−1 to rigorously desorb all guest molecules from the framework. Additionally, the quality of individual samples was confirmed by N2 adsorption isotherms at 77 K, which consistently yielded a Langmuir surface area of 497 ± 6 m²/g. Gas adsorption data were fitted and isosteric heats of adsorption determined following protocols that closely follow a previously used approach[5] and are reproduced here for completeness with new details relevant to this work.

Adsorption isotherm fitting. Adsorption isotherms were fitted with a dual-site Langmuir–Freundlich equation (eq.1), where n is the total amount adsorbed in mmol/g, P is the pressure in bar, nsat,1 is the saturation capacity in mmol/g, bi is the Langmuir parameter in bar−1 defined in eq. 2, and v is the Freundlich parameter for two sites 1 and 2. Experimental adsorption isotherm data for 1 and the corresponding fits show a small discrepancy at higher gas loadings. These may originate from the flexibility of 1 that allows additional small framework deformations as binding site II is occupied at higher gas loadings.

� = ����, ��

� �� + ����,2 �2 ��2

1+�2 ��2 (1)

�� = �–�� ����� (2)

For eq. 2, Si is the entropy of adsorption at saturation in units of R and Ei is the enthalpy of adsorption in kJ/mol, for site i. Also for eq. 2, R is the ideal gas constant and T is the temperature. The fitted parameters for all gases for can be found in tables S1 and S2.

Isosteric heat of adsorption calculations. Using dual-site Langmuir-Freundlich fits, the isosteric heat of adsorption, −Qst, was calculated for each compound as a function of the amount of gas adsorbed using the Clausius-Clapeyron relation (eq. 3), where R is the ideal gas constant, P is the pressure, and T is the temperature.

– � ! = ��" #$ %& �$' (

� (3)

For multi-site Langmuir-Freundlich models, it is necessary to calculate the loading dependence of the isosteric heat of adsorption. As written, multi-site Langmuir-Freundlich equations specify the amount adsorbed as a function of pressure, while the pressure as a function of the amount adsorbed is needed to use the Clausius-Clapeyron relation. To calculate the isosteric heat of adsorption for evenly spaced loadings, each multi-site Langmuir equation was solved for the pressures that correspond to specific loadings of a given gas in the range 77 to 87 K for H2, and 195 to 308 K for CH4. These calculated pressures were then used with eq. 3 to determine the heat of adsorption as a function of the total amount of gas adsorbed.

5

Figure S1. (a – d) 77 K N2 adsorption isotherms of four independent samples of activated 1. The calculated Langmuir surface areas were calculated as described in the General Procedures section and determined at A: 494 m2/g, B: 489 m2/g, C: 514 m2/g, D: 490 m2/g.

Figure S2. (a) Hydrogen adsorption data obtained for 1 at 77 and 87 K (blue and green symbols, respectively) along with fits to a dual-site Langmuir-Freundlich model (black lines). (b) Isotherms of H2 adsorption (solid circles) and desorption (open circles) in 1 at 77 K.

Table S1. Dual-site Langmuir-Freundlich fit parameters for H2 adsorption in 1.

77 K 87 K

qsat,1 3.25 3.18

b1 481 60.0

1 1.30 1.29

qsat,2 4.50 4.50

b2 0.581 0.327

2 0.826 0.813

a b c d

a b

6

Figure S3. Hydrogen adsorption data obtained for 1 at 77 and 87 K (blue and green symbols, respectively) along with fits to a dual-site Langmuir-Freundlich model (black lines), plotted on a logarithmic scale.

Figure S4. CH4 adsorption data obtained for 1 at at 195, 273, 298, and 308 K (colored symbols) along with fits to a dual-site Langmuir-Freundlich model (black lines). (b) Isotherms of CH4 adsorption (solid circles) and desorption (open circles) in 1 at 195 K.

Table S2. Dual-site Langmuir-Freundlich fit parameters for CH4 adsorption in U(bdc)2.

195 K 273 K 298 K 308 K

qsat,1 3.52 3.52 3.52 3.52

b1 81.9 0.680 0.249 0.174

1 1.10 1.10 1.10 1.10

qsat,2 2.00 2.00 2.00 2.00

b2 0.249 0.0302 0.0194 0.0166

2 1.30 1.30 1.30 1.30

a b

7

Figure S5. Isosteric heat of adsorption of CH4 in 1, plotted as a function of gas loading.

4. Thermogravimetric analysis

Figure S6. Thermogravimetric analysis plot for 1–H2O showing a step for the loss of pore water (9.0 wt%, corresponding to 3.2 H2O per pore; inflection point at 120 °C) and a decomposition step (inflection point at 500 °C).

8

5. Powder X-ray diffraction

The Rietveld refinement of the synchrotron X-ray powder diffraction pattern of 1–DMF used rigid body models for the bdc2− ligands and the DMF molecules. The position of the DMF molecules in the framework was found using simulated annealing in real space using Topas Academic[6] followed by a systematic Rietveld refinement of all atomic positions and the occupancy of the solvent molecules.[7]

Figure S7. Powder X-ray diffraction patterns of 1–H2O as generated from single crystal data (black), of 1–H2O as synthesized (blue), and fully activated 1 (green). Experimental powder patterns were recorded at 298 K and are reported for λ = 1.5418 Å.

Figure S8. Rietveld refinement of powder X-ray diffraction pattern obtained for 1–DMF (λ = 0.45246 Å). Black circles show the experimental diffraction pattern and red lines represent the calculated diffraction patterns, respectively. The gray line represents the difference between observed and calculated patterns, and the brown tick marks indicate calculated Bragg peak positions. T = 298 K; λ = 0.45246 Å; Figures-of-merit: Rwp = 7.57, Rp = 5.54, Rexp = 1.02, GoF = 7.43.

9

6. Powder neutron diffraction

Data collection. 0.415 g of pristine crystalline powder of activated 1 was loaded into a cylindrical aluminum sachet and then placed into a cylindrical vanadium can (inner diameter = 6.0 mm). The sample can was sealed with an indium O-ring and a lid with a capillary gas line and a packless valve in a helium-filled glovebox equipped with oxygen and water sensors. The sample was then evacuated at room temperature to approximately 10−6 mbar using a turbomolecular pump, mounted in a bottom-loading closed-cycle refrigerator and cooled under static vacuum. Data were collected for the activated material under static vacuum at 9 K over the course of approximately 24 h. The sample was then warmed to 295 K (subsequent gas dosing was performed at 80 K) and dosed with D2 gas from a known volume (corresponding to ratios of 0.3, 0.7, 1.5, and 2.5 D2 molecules per pore of the MOF), cooled to base temperature of 9 K and measured for approximately 20 h, each. Upon cooling, the outboard pressure indicated the D2 gas had been adsorbed well above base temperature except for the 2.5 equivalents D2

loading, where the adsorption capacity appeared to be reached close to 20 K. After the D2 dosing experiments, the sample was re-activated at 295 K under dynamic vacuum, dosed with 0.7 eq CD4, and then cooled to 7 K to collect for approximately 20 h. The sample was then warmed to 200 K to further dose with CD4 until a total loading of 1.5 equiv. CD4 per MOF pore was reached. The sample was then cooled back to 7 K and another powder pattern was measured at this dosing level. Structure solutions. The powder diffraction data were analyzed using Topas Academic[6] and EXPGUI/GSAS.[3,8] Initial Pawley fits[9] indicated that the activated structure was in a C2/c space group. Upon gas dosing, extra peaks emerged in the powder patterns that could be ascribed to a new crystalline phase with a slight distortion of the parent structure but still within the C2/c space group. The lattice parameters of the gas-dosed structures differ based on the identity of the adsorbate but change very little as a function of concentration of that adsorbate (Table S3). Rietveld refinements[10] of the powder data (Figures S8–S15) yielded the structures of the respective samples. These refinements used bond length and angle restraints for the bdc2− ligands and CD4 gas, as well as a super-atom approach for D2 molecules.[11] The super-atom approach treats the D2 molecule as point scatterers with double occupancy and large thermal parameters. Fourier difference maps for the gas dosed diffraction data were created using the structure solution for the activated material. The Fourier difference maps revealed the approximate position — and, for the CD4 molecules, the orientation — of the gas molecules in the framework in real space. Gas molecules with fixed occupancy based on the known dosing concentrations were added to the framework at these positions. Then, the isotropic thermal parameters and positions of the ligand and gas atoms were refined, as well as the occupancy of the gas atoms. Upon dosing the activated framework 1 with D2 loadings of less than one molecule per binding pocket (i.e. < 2.0 equiv. per pore), the diffraction data shows the convoluted neutron diffraction patterns of phases 1 and 1–D2. The molar ratios of both phases change with the gas loading, causing also the scaling factors of both phases to change. At a D2 loading of 0.3 equiv. the minority phase is 1–D2 and the majority phase is 1, whereas at a gas loading of 1.5 equiv. D2, 1 has become the minority phase, as most of it is has been converted to 1–D2 (now the majority phase). Due to their low signal intensity, the minority phases (i.e. 1–D2 in the 0.3 equiv D2 data, and 1 in the 1.5 equiv D2 dosed data) required additional constraints during the structural refinement, whereas the majority phases were refined as described above. At a loading of 0.7 equiv. D2 both phases 1 and 1–D2 were well enough resolved to be refined using the standard approach described above. For the weakly diffracting minority phases in the 0.3 eq D2 and 1.5 eq D2 gas-dosed patterns, the thermal parameters and atom positions were not refined. When necessary, the occupancies of the gas molecules were fixed to match the dosed concentration value. The Rietveld refinements also yielded the relative phase fractions of the activated and gas-adsorbed structures. The phase fraction of the activated structure decreased monotonically, while the phase fraction of the gas-adsorbed structure increased monotonically as a function of the gas loading in both the D2 and CD4 gas-dosed data sets. At similar gas loadings, the percent conversion from the bare to the gas-dosed structure is similar between the two gases, indicative of a comparable mechanism of structural distortion. In order to further emphasize how structural distortions support the gas adsorption in 1, a hypothetical dummy D2 super-atom was placed in the undistorted activated framework at the fractional coordinates of site I. In this hypothetical undistorted pocket, the distance of D2 to the centroid of the nearest aromatic ring increased from 3.45(1) Å in 1–D2, dosed with 1.5 equiv D2, to 3.91 Å, basically eliminating all stabilizing interactions. Analogously, the distance from D2 to the centroid of the nearest triangular face of the UO8 node elongated from 3.52(2) to 4.01 Å, preventing effective host-guest interactions. We note that although great care was taken in this approach, the required use of fractional coordinates in combination with the reported structural differences between 1 and 1–D2, introduces unknown but non-negligible uncertainties to the reported contact distances between the generated dummy atom and the experimentally confirmed activated framework structure. Accordingly, these values can only serve as an estimate, although they confirm that the strong adsorption site I – as determined in 1–D2 – would be too distant from all relevant adsorption features of the binding pocket in 1 to allow reasonable interactions without pore contraction. In order to further describe the binding pocket contraction of 1 in response to different adsorbates, diameters of approximated spherical binding pockets were determined based on crystallographic structure data. First, the geometric centroid of a binding pocket was calculated in each structure. Then, a sphere was generated around this centroid such that the sphere did not make contact with any atom of the pore, based on van der Waals radii. The diameter of the resulting sphere around the centroid was then reported as the approximated binding pocket diameter. Binding pocket diameters were determined at 5.0, 3.6, 4.1, and 4.2 Å for activated 1, 1–D2 (dosed with 2.5 equiv. D2), 1–CD4 (dosed with 1.5 equiv. CD4), and 1–DMF, respectively.

10

Figure S9. Rietveld refinement of the powder neutron diffraction pattern obtained for activated phase 1 (λ = 2.0772 Å; T = 9 K). Black circles show the experimental diffraction pattern and the red line represents the calculated diffraction pattern. The gray line represents the difference between observed and calculated patterns, the blue tick marks indicate calculated Bragg peak positions of the activated phase 1, and the pink tick marks indicate reflections from the aluminum sachet.

Figure S10. Rietveld refinements of powder neutron diffraction patterns obtained for 1, dosed with 0.3 equivalents of D2 per pore (λ = 2.0772 Å; T = 9 K). Black circles show the experimental diffraction pattern and red lines represent the calculated diffraction patterns. The gray lines represent the difference between observed and calculated patterns, the blue tick marks indicate calculated Bragg peak positions of the activated phase 1, the purple tick marks indicate calculated Bragg peak positions of the D2 adsorbed phase 1–D2, and the pink tick marks indicate reflections from the aluminum sachet.

11

Figure S11. Rietveld refinements of powder neutron diffraction patterns obtained for 1, dosed with 0.7 equivalents of D2 per pore (λ = 2.0772 Å; T = 9 K). Black circles show the experimental diffraction pattern and red lines represent the calculated diffraction patterns. The gray lines represent the difference between observed and calculated patterns, the blue tick marks indicate calculated Bragg peak positions of the activated phase 1, the purple tick marks indicate calculated Bragg peak positions of the D2 adsorbed phase 1–D2, and the pink tick marks indicate reflections from the aluminum sachet.

Figure S12. Rietveld refinements of powder neutron diffraction patterns obtained for 1, dosed with 1.5 equivalents of D2 per pore (λ = 2.0772 Å; T = 9 K). Black circles show the experimental diffraction pattern and red lines represent the calculated diffraction patterns. The gray lines represent the difference between observed and calculated patterns, the blue tick marks indicate calculated Bragg peak positions of the activated phase 1, the purple tick marks indicate calculated Bragg peak positions of the D2 adsorbed phase 1–D2, and the pink tick marks indicate reflections from the aluminum sachet.

12

Figure S13. Rietveld refinements of powder neutron diffraction patterns obtained for 1, dosed with 2.5 equivalents of D2 per pore (λ = 2.0772 Å; T = 9 K). Black circles show the experimental diffraction pattern and red lines represent the calculated diffraction patterns. The gray lines represent the difference between observed and calculated patterns, the purple tick marks indicate calculated Bragg peak positions of the D2 adsorbed phase 1–D2, and the pink tick marks indicate reflections from the aluminum sachet.

Figure S14. Rietveld refinements of powder neutron diffraction patterns obtained for 1, dosed with 0.7 equivalents of CD4 per pore (λ = 2.0772 Å; T = 7 K). Black circles show the experimental diffraction pattern and red lines represent the calculated diffraction patterns. The gray lines represent the difference between observed and calculated patterns, the blue tick marks indicate calculated Bragg peak positions of the activated phase 1, the orange tick marks indicate calculated Bragg peak positions of the CD4 adsorbed phase 1–CD4, and the pink tick marks indicate reflections from the aluminum sachet.

13

Figure S15. Rietveld refinements of powder neutron diffraction patterns obtained for 1, dosed with 1.5 equivalents of CD4 per pore (λ = 2.0772 Å; T = 7 K). Black circles show the experimental diffraction pattern and red lines represent the calculated diffraction patterns. The gray lines represent the difference between observed and calculated patterns, the orange tick marks indicate calculated Bragg peak positions of the CD4 adsorbed phase 1–CD4, and the pink tick marks indicate reflections from the aluminum sachet.

Table S3. Figures of merit and unit cell parameters (space group C2/c) obtained from Rietveld refinements to the neutron powder diffraction data measured at 9 K as presented in figures S9 – S15. Values in parenthesis indicate one standard deviation.

Rwp Rp Rexp GoF 2 a (Å) b (Å) c (Å) V (Å3)

1, activated 0.0228 0.0186 0.0203 1.14 1.265 17.587(1) 12.812(1) 9.2999(5) 90 114.814(4) 90 1902.1(2)

1 + 0.3 eq. D2 0.0245 0.0200 0.0216 1.13 1.280 18.361(7) 11.35(1) 9.335(2) 90 113.64(3) 90 1782(2)

1 + 0.7 eq. D2 0.0252 0.0207 0.0221 1.16 1.283 18.402(3) 11.324(5) 9.333(1) 90 113.659(8) 90 1781.4(8)

1 + 1.5 eq. D2 0.0242 0.0195 0.0215 1.14 1.268 18.456(1) 11.233(1) 9.3508(4) 90 113.648(3) 90 1775.8(2)

1 + 2.5 eq. D2 0.0223 0.0185 0.0214 1.06 1.088 18.665(1) 10.9486(8) 9.3838(5) 90 113.807(3) 90 1754.5(2)

1 + 0.7 eq. CD4 0.0274 0.0224 0.0240 1.17 1.301 17.968(2) 12.098(2) 9.3121(6) 90 114.006(4) 90 1849.1(4)

1 + 1.5 eq. CD4 0.0260 0.0212 0.0222 1.18 1.358 18.031(1) 11.9665(7) 9.3206(4) 90 113.856(3) 90 1839.3(2)

14

7. Single crystal X-ray diffraction

Single crystals of 1–H2O were coated in paratone oil under air prior to transport to the Advanced Light Source at Lawrence Berkeley National Lab (station 12.2.1). Crystals were evaluated by polarized light microscopy and mounted on a MiTeGen 10 μm aperture Dual-Thickness MicroMount. X-ray diffraction data were collected with a silicon monochromated synchrotron radiation beam of 17 keV (λ = 0.7288 Å). The crystal was cooled to 100 K with a dry nitrogen stream. Bruker APEX3 software was used for the data collections,[12] Bruker SAINT V8.38A software was used to conduct the cell refinement and data reduction procedures.[13] Absorption corrections were carried out by a multi-scan method utilizing the SADABS program.[14] The initial structure solution was found using direct methods (SHELXS), and refinements were carried out using SHELXL-2014.[15] Thermal parameters for all non-hydrogen atoms were refined anisotropically and all framework hydrogens were refined using the riding model. The pore water molecules in 1–H2O were disordered and could not be modeled with high precision; however, the pore water oxygens (four per MOF pore, in agreement with TGA analysis) were located from the Fourier difference map and were allowed to refine freely without restraints or constraints and without hydrogen atoms. The structure of 1–H2O has been deposited to the Cambridge Crystallographic Data Centre (CCDC), with deposition number 1996337.

Table S4. Single crystal X-ray diffraction data and structure refinement details for 1–H2O.

parameter 1–H2O

Formula C16H8O12U

Formula weight 630.25

Temperature (K) 100

Crystal size (mm3) 0.035 × 0.005 × 0.005

Crystal System monoclinic

Space Group C2/c

a, b, c (Å) 17.7447(17), 12.5982(12), 9.2934(8)

α, β, γ(°) 90, 114.702(4), 90

V, (Å3) 1887.4(3)

Z / Z′′ 8 / 4

Radiation, λ (Å) 0.7288

2Θ Range for Data Collection (°) 5.182 to 54.19

Completeness (%) to 2Θ = 51.86 ° 99.9

Data / Restraints / Parameters 1944 / 0 / 133

Goodness of Fit on F2 1.087

R1a, wR2

b (I > 2σ (I)) 0.0531, 0.1493

R1a, wR2

b (all data) 0.0667, 0.1605

Peak and Hole (e Å–3) 2.33, −1.95

a � = ∑*|,-| – |,.|*∑|,-| b /�" = 0∑123,-4 – ,.4546

∑123,-4546 74

15

Table S5. Selected bond distances in Å and angles in degrees for 1–H2O. Angles φ1 and φ2 describe the U···U···U angles of the idealized parallelogram spanned by the four corner U atoms within the crystallographic ab plane of each pore, as illustrated in Figure 5a of the main text. Angle φ1 is reported as the average between the two angles φ1a and φ1b, which slightly deviate from one another due to a three-dimensional distortion of the idealized parallelogram. Angles ω1 and ω2 describe the dihedral angle between O–U···U–O planes and O–C–O planes at each side of a bdc2– linker, as illustrated in Figure 5b of the main text. Values in parenthesis indicate one standard deviation.

U–O (Å) a ∠O–U–O(°) b φ1 (°) φ2 (°) ω1 (°) ω2 (°)

1–H2O

2.398(7) 2.312(8) 2.300(7) 2.377(7)

73.1(3) 71.9(3) 75.5(3) 72.4(3)

115.1(3) 114.8(3)

75.639(3) 104.361(1) 154.4(9) 174.7(9)

a The two squares formed by the eight oxygen atoms coordinated to each U ion in square anti-prismatic geometry are related by symmetry, resulting in a total of four independent U–O bonds.

b The two squares formed by the eight oxygen atoms coordinated to each U ion in square anti-prismatic geometry are related by symmetry, resulting in six independent O–U–O angles that can be constructed between all oxygen atoms of one plane and the uranium ion.

Figure S16. (a) Graphical representation of single crystal structure data obtained for 1–H2O, including the refined oxygen atoms of H2O molecules adsorbed in the pores, shown in a larger fraction of the structural with multiple pores. (b) Graphical representation of one pore with viewing direction along the crystallographic c-axis. (c) Graphical representation of the same pore as in (b), but rotated by 90°. Orange, red, grey, and white spheres represent U, O, C, and H atoms, respectively.

a b c

16

Figure S17. Graphical representation of single crystal structure data obtained for 1–H2O, truncated to show the uranium chains that propagate along the crystallographic c-axis of 1–H2O. Orange, red, and grey spheres represent U, O, and C atoms, respectively.

17

8. References

[1] M. J. Monreal, R. K. Thomson, T. Cantat, N. E. Travia, B. L. Scott, J. L. Kiplinger, Organometallics 2011, 30, 2031. [2] J. A. Mason, J. Oktawiec, M. K. Taylor, M. R. Hudson, J. Rodriguez, J. E. Bachman, M. I. Gonzalez, A. Cervellino, A.

Guagliardi, C. M. Brown et al., Nature 2015, 527, 357. [3] A. C. Larson, R.B. von Dreele, "General Structure Analysis System (GSAS)", Los Alamos National Laboratory Report

LAUR 2000, 86. [4] C. Falaise, A. Assen, I. Mihalcea, C. Volkringer, A. Mesbah, N. Dacheux, T. Loiseau, Dalton Trans. 2015, 44, 2639. [5] D. E. Jaramillo, D. A. Reed, H. Z. H. Jiang, J. Oktawiec, M. W. Mara, A. C. Forse, D. J. Lussier, R. A. Murphy, M.

Cunningham, V. Colombo et al., Nat. Mater. 2020, DOI: 10.1038/s41563-019-0597-8. [6] A. Coelho, Topas Academic v6 Coelho Software 2017, http://www.topas-academic.net/. [7] Y. G. Andreev, G. S. MacGlashan, P. G. Bruce, Phys. Rev. B 1997, 55, 12011. [8] B. H. Toby, J. Appl. Cryst. 2001, 34, 210. [9] G. S. Pawley, J. Appl. Cryst. 1981, 14, 357. [10] H. M. Rietveld, J. Appl. Cryst. 1969, 2, 65. [11] a) T. Runčevski, M. T. Kapelewski, R. M. Torres-Gavosto, J. D. Tarver, C. M. Brown, J. R. Long, Chem. Commun. 2016,

52, 8251; b) R. A. Pollock, J.-H. Her, C. M. Brown, Y. Liu, A. Dailly, J. Phys. Chem. C 2014, 118, 18197; c) H. Wu, W. Zhou, T. Yildirim, J. Am. Chem. Soc. 2007, 129, 5314.

[12] APEX3 Version 2016.1-0 ed., Bruker AXS, Inc.: Madison, WI, USA 2016. [13] SAINT Version 8.38A ed., Bruker AXS, Inc.: Madison, WI, USA. [14] Sheldrick, George M., Bruker AXS, Inc.: Madison, WI, USA, SADABS, Version 2014/4 2014. [15] a) G. M. Sheldrick, Acta. Cryst. A 2008, 64, 112; b) O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H.

Puschmann, J. Appl. Cryst. 2009, 42, 339; c) L. J. Farrugia, J. Appl. Cryst. 2012, 45, 849.

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