doi.org/10.26434/chemrxiv.9992402.v1
Probing the Inverse Trans Influence in Americium and LanthanideTribromide Tris(tricyclohexylphosphine oxide)Cory Windorff, Cristian Celis-Barros, Joseph Sperling, Noah Mckinnon, Thomas Albrecht-Schmitt
Submitted date: 16/10/2019 • Posted date: 21/10/2019Licence: CC BY-NC-ND 4.0Citation information: Windorff, Cory; Celis-Barros, Cristian; Sperling, Joseph; Mckinnon, Noah;Albrecht-Schmitt, Thomas (2019): Probing the Inverse Trans Influence in Americium and LanthanideTribromide Tris(tricyclohexylphosphine oxide). ChemRxiv. Preprint.
The synthesis, characterization, and theoretical analysis of meridional americium tribromidetris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy3)3 has been achieved and is compared with its earlylanthanide (La to Nd) analogs. The data show that homo trans ligands show significantly shorter bonds thanthe cis or hetero trans ligands. This is particularly pronounced in the americium compound. DFT along withmulticonfigurational CASSCF calculations show that the contraction of the bonds relates qualitatively withoverall covalency, i.e. americium shows the most covalent interactions compared to lanthanides. . However,the involvement of the 5p and 6p shells in bonding follows a different order, namely cerium > neodymium ~americium. This study provides further insight into the mechanisms by which ITI operates in low-valent f-blockcomplexes.
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1
Probing the inverse trans influence in americium and lanthanide
tribromide tris(tricyclohexylphosphine oxide)†
Cory J. Windorff, Cristian Celis-Barros, Joseph M. Sperling, Noah C. McKinnon, Thomas E.
Albrecht–Schmitt*
Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, RM. 118 DLC,
Tallahassee, Florida 32306, USA. E-mail: [email protected];
†Electronic supplementary information (ESI) available. Photographs of compounds, NMR spectra, electronic
absorption spectra, additional theoretical calculation and crystallographic details for CCDC #######–#######.
ORCID: Cory J. Windorff: 0000-0002-5208-9129; Cristian Celis-Barros: 0000-0002-4685-5229; Joseph M.
Sperling: 0000-0003-1916-5633; Thomas E. Albrecht-Schmitt: 0000-0002-2989-3311
Abstract
The synthesis, characterization, and theoretical analysis of meridional americium tribromide
tris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy3)3 has been achieved and is compared
with its early lanthanide (La to Nd) analogs. The data show that homo trans ligands show
significantly shorter bonds than the cis or hetero trans ligands. This is particularly
pronounced in the americium compound. DFT along with multiconfigurational CASSCF
calculations show that the contraction of the bonds relates qualitatively with overall
covalency, i.e. americium shows the most covalent interactions compared to lanthanides. .
However, the involvement of the 5p and 6p shells in bonding follows a different order,
namely cerium > neodymium ~ americium. This study provides further insight into the
mechanisms by which ITI operates in low-valent f-block complexes.
2
Introduction
Phosphine oxides are highly stable ligands that have been utilized primarily for catalysis on
elements across the periodic table.1 The study of phosphine oxides with f-elements has
primarily focused on their use in extraction processes2-5
and in (pseudo)halide/nitrate f-
element starting materials.6-9
The effect of two ligands trans to one another is most
prototypically examined in the actinyls, AnO2n+
, where the trans-oxygens display unusually
short bond distances and high bond strength, best described as bond order of three.10
This
effect, termed the inverse trans influence (ITI) has become the focus of several experimental
and theoretical investigations.11-17
A prototypical examination on the effect of ITI is through
the use or meridional octahedral compounds, e.g. mer-MX3L3 Figure 1, which has been
thoroughly studied in the transition metal series, but is significantly less studied in the f-
block.18
However, the primary focus of structural and theoretical studies on actinide
molecules displaying the ITI effect have been focused on high valent, +4 to +6, oxidation
states.13, 19
Lanthanides have only been subjected to structural studies in the +3 oxidation
state,12, 20
with some analysis of Ce(IV) and hypothetical Pr(IV) and Tb(IV) molecules.15, 17
The amount of ITI can be quantified as a percentage that implies that the lower the
percentage value the larger the ITI effect, Equation 1, where r = bond distance, M = metal, X
= neutral or anionic ligand.21
ITI =r(M − Xtrans)
r(M − Xcis)x100
(1)
3
The minor actinides, Am and Cm, contribute high levels of radiation and heat in spent
nuclear fuel. Long-lived isotopes of Am [241
Am (t1/2 = 432 y), 243
Am (t1/2 = 7370 y)] can be
transmuted into radionuclides with a much shorter-half life, which is important for the end of
the nuclear fuel cycle. However, the separation of these minor actinides from other fission
products, such as lanthanides, remains a difficult problem. The additional separation of
AmIII
/CmIII
is a great challenge due to their similar chemical properties and ionic radii.
Phosphine oxide ligands have recently demonstrated relatively high selectivity for the Am-
Cm pair in the form of (Ph2PyPO)2M(NO3)3.22
Although phosphine oxides are heavily
utilized in separation of f-elements relevant to the nuclear fuel cycle, there have been few
crystallographic studies for trans-uranium elements, and indeed only the mono and bis[Opy-
2,6-CH2(Ph)2PO], NOPOPO, adducts has been reported.23
Herein we examine the synthesis
and structure in saturated tri-cyclohexylphosphine oxide adducts of f-element tribromides,
and the effects of the ITI on tri-valent f-elements.
Figure 1. General depiction of ligand designations in mer-MX3L3.
4
Experimental Details
General Considerations. Caution! 243
Am (t1/2 = 7,364 years) and its daughters have high
specific activity α-particle and, γ emitting radionuclides, and its use presents extreme hazards
to human health. This research was conducted in radiological and nuclear facilities with
appropriate analyses of these hazards and implementation of controls for the safe handling
and manipulation of these toxic and radioactive materials.
Materials. All experiments were conducted in air with no attempt to exclude air or water.
Reagents and solvents, OPcy3 (cy = cyclohexyl, C6H11, Alfa Aesar), CDCl3 (Cambridge),
iPrOH (Sigma) NH3(aq) (Baker) were purchased from commercial sources and used as
received. LnBr3•6H2O (Ln = La – Nd) were synthesized by dissolution of Ln2O3 in
concentrated HBr and heated at 150 °C in a box furnace until viscous, then agitated, stirred
until cooled to room temperature, dissolved in water and boiled down. This process was
repeated twice. The product was washed with ether, to remove residual acid and Br2, until
washings were colorless, dried under house vacuum for 10-15 min and stored in a desiccator
and used with the assumed hydration number of six. All 243
Am synthetic manipulations were
performed in a certified chemical fume hood, and a known concentration stock solution was
prepared as previously described.24
Aqueous manipulations were performed with >18 Ω
water from a Millipore purification system.
Instrumentation. All 1H,
13C{
1H} and
31P{
1H} NMR spectra were recorded at 294(2) K on a
Bruker 600 MHz NMR spectrometer operating at 600.13, 150.90, and 242.94 MHz,
respectively, for all lanthanide samples; the sample of 243
AmBr3(OPcy3)3 was recorded at
295(2) K on a Bruker 400 MHz NMR spectrometer operating at 400.17, 100.62, and 161.99
MHz, respectively. 1H and
13C{
1H} were referenced to internal solvent resonances,
31P{
1H}
spectra were referenced externally to 85% H3PO4. For radiologic containment,
243AmBr3(OPcy3)3 was dissolved in minimal CDCl3, transferred to a PTFE NMR tube liner,
5
sealed, checked for contamination, placed inside a high quality borosilicate NMR tube, and
checked again for contamination before being transported to the spectrometer. Due to the
paramagnetism of Am3+
, Ce3+
, Pr3+
and Nd3+
, and in particular the small sample size of
243AmBr3(OPcy3)3, only unambiguously identifiable peaks are assigned. Single crystal
UV/vis/NIR measurements were made using a CRAIC microphotospectrometer on single
crystals from 320 to 1700 nm. Single crystals of the lanthanide complexes were mounted on
nylon cryoloops with Paratone-N oil. Crystals of 243
AmBr3(OPcy3)3 was mounted with
appropriate layers of containment. Crystallographic data from all single crystals were
collected on a Bruker D8 Quest diffractometer with a Photon 100 complementary metal-
oxide-semiconductor (CMOS) detector, and cooled to 120(2) or 130(2) K using an Oxford
Cryostream or CRYO Industries low-temperature device. The instrument was equipped with
graphite monochromatized Mo Kα X-ray source (λ = 0.71073 Å). The APEX325
program
package was used to determine the unit-cell parameters and for data collection. The raw
frame data was processed using SAINT26
and SADABS27
to yield the reflection data file.
Subsequent calculations were carried out using the SHELXTL28, 29
or OLEX230
programs.
Theoretical Methods. The coordinates of MBr3(OPcy3)3 (M = Am, Ce, Nd) for the
calculations were obtained directly from the crystal structure to keep the constraints imposed
by the solid-state packing. To utilize multiconfigurational calculations, the complete active
space self-consistent field (CASSCF) approximation31
was used as implemented in the
ORCA 4.1.1 program.32
Wave functions were obtained utilizing the SARC-TZVP basis set
for the metal centers and the Def2-TZVP basis functions for the rest of the atoms. The active
space considered were n electrons (n = 1, 3, 6 for Ce, Nd, and Am) in the seven f orbitals
giving rise to a CAS(n,7). Scalar relativistic effects were included by the second-order
Douglas-Kroll-Hess (DKH2) Hamiltonian. State interactions via quasi-degenerate
perturbation theory (QDPT) were used to correct the wave function for spin-orbit coupling
6
(SOC). The resulting wave functions (SO-CAS) were used to analyze the nature of the
ground and low-lying excited states, whereas the scalar relativistic wave functions (SR-CAS)
were used for further bonding analysis.
The nature of the chemical bonds was addressed performing a topological analysis of
the electron density using Bader’s quantum theory of atoms in molecules (QTAIM) analysis.
Key elements within QTAIM were extracted such as the electron density, delocalization
indices, and energy densities at the interatomic region (bond critical point, BCP) which have
been employed previously for this aim.33-41
The covalency was analyzed, on one hand, by
changes in the concentration of the electron density at the BCP along with changes in the
delocalization indices. On the other hand, energy densities show the polarization of the
covalent bond by looking at the ratios between potential [V(r)] and kinetic [G(r)] energy
densities, which for partial covalent bonds lie in between values of 1 and 2. The total energy
density shows the degree of covalency that is represented by the level of predominance of the
potential over the kinetic energy density.42
A model system was also investigated where the cyclohexyl groups were replaced by
methyl groups to simplify the molecular orbital energy diagram picture and allow the
observations between the Am, Ce and Nd complexes to be made. The methyl groups were re-
optimized while the rest of the molecule was kept frozen to conserve the crystal structure of
the metal surrounding atoms. These calculations were performed in the ADF2019 suite43, 44
using the PBE functional along with the TZP basis set. Frozen-core and all-electron
calculations were performed for the full structure to prove the role of 5/6p orbitals in the
stabilization of the complexes at the same level of theory. Additionally, ligand-field DFT45, 46
was used to examine the reduction of the inter–electronic repulsion within the 5/6p shell due
to central-field and symmetry-restricted covalency. The procedure used herein has been
previously described for Cs2KYF6:Pr3+
,45
where occupation numbers in the f-shell were
7
allowed to be fractional. The reductions were obtained not only with respect to the free-ions
but also compared to the nona-aquo complexes, [M(H2O)9]3+
, where the geometries were
taken from the crystalized structures in the literature.47-49
Synthesis of 243
AmBr3(OPcy3)3. An aliquot of 243
Am (3.0 mg, 12 µmol) was drawn from a 2
M HCl stock solution and precipitated with excess NH3(aq) to give a pale yellow solid naïvely
formulated as Am(OH)3, washed with water (2 × 2 mL), suspended in ~ 1 mL of water and
dissolved with HBr (concentrated, ~0.5 mL) to give a yellow solution. The yellow solution
was transferred to a 20 mL scintillation vial, placed under a heat lamp and gently evaporated
to a yellow residue formulated as AmBr3•nH2O. The residue was dissolved in iPrOH (1.50
mL) to give a dark yellow solution. A colorless solution of OPcy3 (11 mg, 38 µmol) in iPrOH
(1.00 mL) was added to the Am solution, which quickly became turbid and clear again. The
solution was capped and left to stand undisturbed. Over 3 h amber colored X-ray quality
crystals were deposited. A small sample was withdrawn for spectroscopy (single crystal X-
ray diffraction and solid state UV/vis/NIR). The solution was capped and left to stand for 3
days to allow further crystallization. The mother liquor was decanted, washed with Et2O (3 ×
0.5 mL), dried in air and transferred to a glovebox dedicated to actinide chemistry to give
AmBr3(OPcy3)3 as a yellow/brown crystalline solid, 9.0 mg, 54%. 1H NMR (CDCl3; 400
MHz) δ: 1.80 (br, s, cy), 1.67 (br, s, cy), 1.39 (br, s, cy), 1.14 (br, s, cy); 13
C{1H} NMR
(CDCl3; 101 MHz) δ: 27.08 (2JPC = 27 Hz, cy), 26.15 (cy) 25.90 (cy);
31P{
1H} NMR (CDCl3;
162 MHz) δ: 108.89 (s, ν1/2 141.1 Hz). Due to the weak paramagnetism and small sample
size 1H integration is ambiguous and
1H and
13C{
1H} peak assignments are tentative, see ESI.
UV/vis/NIR [λmax, nm (cm−1
), single crystal]: 340.0 nm (29,411) charge transfer, 368.4
(27,148) 5G2′, 380.9 (26,252)
5G4′, 433.4 (23,074)
5H4′, 457.5 (21,856)
5G2′, 477.0 (20,695)
5D2′, 508.0 (19,685)
5L6′, 524.2 (19,075)
5L6′, 777.4 (12,863)
7F6′, 805.8 (12,422)
7F6′, 823.2
(12,147) 7F6′, 1042.6 (9591)
7F4′.
8
General Synthesis of LnBr3(OPcy3)3, (Ln = La, Ce, Pr, Nd). As an alternative to the
literature50
a colorless solution of OPcy3 (18 mg, 61 µmol) in iPrOH (1.0 mL) was added to a
yellow solution of LnBr3•6H2O (~10 mg, ~20 µmol) in iPrOH (1.5 mL) causing the solution
to become turbid and then clear. The vial was capped and left to stand overnight during
which colorless X-ray quality crystals were deposited. A small sample was withdrawn for
spectroscopy (single crystal X-ray diffraction and solid state UV/vis/NIR). The mother liquor
was decanted, washed with Et2O (3 × 0.5 mL), dried in air and briefly dried under reduced
pressure to give LnBr3(OPcy3)3 as a crystalline solid. All products were confirmed by single
crystal X-ray crystallography.
LaBr3(OPcy3)3. Colorless LaBr3(OPcy3)3 20 mg, 80%. 1H NMR (CDCl3; 600 MHz) δ: 4.305
(s, 2H, H2O), 2.068 (m, 8H, cy), 1.991 (m, 18H, cy), 1.842 (m, 18H, cy), 1.700 (m, 9H, cy),
1.600 (m, 18H, cy), 1.352 – 1.261 (m, 28H, cy); 13
C{1H} NMR (CDCl3; 151 MHz) δ: 34.772
(1JCP = 34.8 Hz, i-cy), 26.893 (
2JCP = 26.94 Hz, cy), 25.996 (cy), 25.901 (cy);
31P{
1H} NMR
(CDCl3; 243 MHz) δ: 60.314 (s, ν1/2 151.9 Hz).
CeBr3(OPcy3)3. Orange CeBr3(OPcy3)3 20 mg, 75%. 1H NMR (CDCl3; 600 MHz) δ: 5.29
(br, s, 9H, cy), 3.64 (br, s, 18H, cy), 2.68 (br, s, 18H, cy), 2.01 (s, 18H, cy), 1.82 (s, 25H, cy),
1.22 (br, s, 10H, cy); 13
C{1H} NMR (CDCl3; 151 MHz) δ: 38.76 (
1JCP = 38.8 Hz, i-cy), 27.51
(cy), 26.06 (cy); 31
P{1H} NMR (CDCl3; 243 MHz) δ: 109.48 (s, ν1/2 240.4 Hz). UV/vis/NIR
[λmax, nm (cm−1
), single crystal]: 339.8 (29,479) charge transfer.
PrBr3(OPcy3)3. Colorless PrBr3(OPcy3)3 22 mg, 83%. 1H NMR (CDCl3; 600 MHz) δ: 20.85
(br, s, ν1/2 = 1468 Hz, 5H, cy), 13.55 (br, s, ν1/2 = 862 Hz, 16H, cy), 10.52 (br, s, ν1/2 = 926
Hz, 14H, cy), 4.8 (br, s, 20H, cy), 3.40 (br, s, 21H, cy), 2.72 (br, s, 12H, cy), 1.44 (br, s, 11H,
cy); 13
C{1H} NMR (CDCl3; 151 MHz) δ: 36.94 (cy), 30.54 (cy), 27.70 (cy);
31P{
1H} NMR
(CDCl3; 243 MHz) δ: 212.4 (s, br, ν1/2 4290).
9
NdBr3(OPcy3)3. Pale green NdBr3(OPcy3)3 19 mg, 82%. 1H NMR (CDCl3; 600 MHz) δ:
11.77 (br, s, ν1/2 = 590 Hz, 8H, cy), 7.39 (br, s, ν1/2 = 320Hz, 17H, cy, overlapping with
CDCl3), 5.53 (br, s, ν1/2 = 400 Hz, 17H, cy), 3.05 (br, s, 18H, cy), 2.53 (br, s, 19H, cy), 2.14
(br, s, ν1/2 = 11H, cy), 1.21 (br, s, 11H, cy); 13
C{1H} NMR (CDCl3; 151 MHz) δ: 30.95 (cy),
28.54 (cy), 26.66 (cy); 31
P{1H} NMR (CDCl3; 243 MHz) δ: 190.2 (s, br, ν1/2 1366 Hz).
UV/vis/NIR [λmax, nm (cm−1
), single crystal]: 532.0 (18,798), 572.8 (17,459), 576.6 (17,342),
584.3 (17,114), 588.1 (17,003), 591.9 (16,893), 595.0 (16,806), 599.6 (16,678), 607.3
(16,467) all excitations belong to 4G7/2,
4G5/2.
Results and Discussion
Synthesis. Previously published literature on LnCl3(OPR3)x show that the products have poor
solubility or are prone to speciation.51-53
The more solubilizing bromide anion was studied
instead. The known mer-LnBr3(OPcy3)3 (mer = meridional; cy = cyclohexyl, C6H11) have
been recently reported and give opportunity for extension to the trivalent actinides, though
small lanthanides can speciate.50, 54-56
There has been just one report of a single crystal Am–
Br compound, AmBr3(THF)4.57
The previously reported syntheses of mer-LnBr3(OPcy)3, (cy = cyclohexyl, C6H11)
utilized boiling ethanol and describe the complexes as having low solubility.50
By changing
the alcohol to iso-propyl alcohol (iPrOH) and working on a scale relevant to actinides, ie ≤
0.02 mmol of metal content, a smooth synthesis is obtained. This was extended to americium
by starting from a stock solution of AmCl3•nH2O in HCl, precipitating the hydroxide and
dissolving the product in HBr(aq) and evaporated to dryness forming a putative AmBr3•nH2O.
Combining the components in iPrOH initially forms a turbid solution which clarified within
minutes and upon standing at room temperature, amber colored X-ray quality crystals formed
10
within 2 h, Equation 2. A small sample was removed for spectroscopy and the solution was
left to stand several days to increase the crystalline yield before work up, Figure 2.
Figure 2. Thermal ellipsoid plot of AmBr3(OPcy3)3 drawn at the 50% probability level with
hydrogen atoms omitted for clarity.
Crystallography. AmBr3(OPcy3)3 crystallizes as the meridional isomer, mer-
AmBr3(OPcy3)3, in the orthorhombic Pca21 space group and is isomorphous with its
lanthanide analogs.25
Based on the Flack parameter, a small (≤ 3%) enantiomorphic twin was
dealt with using a TWIN/BASF refinement, see ESI.58
The Am–Br bond lengths fall into two
Am1
Br3
Br1
Br2
O1 O2
O3
P1 P2
P3
11
classes, that of axial (ax) and equatorial (eq) ligands, where axial ligands consistent of a
homo-ligand trans to the ligand of interest, and equatorial ligands where a hetero ligand is
trans to the ligand of interest, Figure 1. The Am–Oax bond lengths are 2.302(7), and 2.312(7)
Å while the Am–Oeq bond is 2.349(6) Å, a separation of 3σ. The Am–Brax atoms display a
bond distance of 2.870(1), and 2.882(1) Å and the Breq atom displays a significantly longer
distance of 2.912(1) Å. These values are all significantly longer than the 2.8222(6),
2.8445(6), and 2.8610(6) Å bond lengths reported in AmBr3(THF)4.57
However, all of the
2.466(4)–2.533(4) Å Am–OTHF bond lengths in AmBr3(THF)4 are significantly longer than
Am–O bond lengths in AmBr3(OPcy3)3. The 2.34(1)–2.51(1) Å Am–O bond lengths reported
for the NOPOPO ligand in Am(NOPOPO)(NO3)3 and [Am(NOPOPO)2(NO3)][NO3]2
[NOPOP = Bis[(phosphino)methyl]pyridine-1-oxide, Opy-2,6-CH2(Ph)2PO] are only
comparable to 2.349(6) Å Am–Oeq bond since the Am–Oax bond lengths are all significantly
shorter, Table 1.23
All of the X–Am–Y bond angles are between 85.2(2)–95.60(5)° for cis
ligands and 172.74(3)–178.1(2)° for trans ligands, see ESI.
Table 1. Comparisons of Am–O bond lengths (Å) in selected Am complexes.
Am–OPcy3ax Am-OPcy3eq Am–ONL Am–OPL
AmBr3(OPcy3)3 2.302(7), 2.312(7) 2.349(6)
Am(L)(NO3)323
2.417(9) 2.38(1), 2.39(1)
[Am(L)2(NO3)][NO3]223
2.51(1)
2.506(9)
2.39(1), 2.34(1),
2.38(1), 2.34(1)
L = NOPOPO, Opy-2,6-CH2(Ph)2PO
In the course of preparing the synthesis of mer-AmBr3(OPcy3)3, the analogous
lanthanides, La–Nd, were examined using the modified synthesis stated above, since the 6-
coordinate radius of Am3+
, 0.975 Å, is most closely related to Nd3+
, 0.983 Å.59
It was found
12
that the Nd and Pr analogs, mer-LnBr3(OPcy3)3, are isomorphous with the previously
reported structures, except the half occupied lattice water was not located in our structures,
see ESI.50
The Ce analog, mer-CeBr3(OPcy3)3 is not yet reported and the structure was
collected. The La analog was reported in the P21 space group with a lattice ethanol molecule,
mer-LaBr3(OPcy3)3•EtOH, however upon synthesis in iPrOH, the isomorphous Pca21 unit
cell was obtained and is reported here, see ESI. Crystals of CeBr3(OPcy3)3 are orange, while
crystals of the La, Pr and Nd analogs are all colorless. Bulk samples of PrBr3(OPcy3)3 and
NdBr3(OPcy3)3 are pale yellow and pale green, respectively. The bond metrics of the
lanthanides examined here all display the same axial/equatorial bonding patterns, that being
axial ligands display much shorter bond lengths than equatorial ligands, with distorted
octahedral geometries, see ESI.
With this data in hand, the calculations of ITI effect from Eq. 1 were carried out on
the MBr3(OPcy3)3 (M = Am, La, Ce, Pr, Nd) complexes examined here. The data show that a
subtle increase in ITI effect is seen with decreasing ionic radius, Table 2, all of the data are
within the error of one another. When the ITI calculations were repeated using the
crystallographic data for the previously published LnBr3(OPcy3)3 compounds (Ln = La, Pr,
Nd, Gd, Ho), as well as LnI3(Et2O)3,20
LnCl3(HMPA)3,60-62
and the series YbX3(THF)3 (X
= Cl, Br, I).11, 63, 64
The data shows no clear trends or patterns with respect to lanthanide or
halide identity, where the halide ligands usually show no ITI. The oxygen donors follow the
pattern in terms of ITI values where: Et2O > THF > HMPA, which appears counter intuitive
since HMPA is regarded as a strong donor, while Et2O is regarded as a weak donor, see ESI
for data tables. Without more sophisticated investigations and based on these small data sets,
it is not clear what ligands affect the values for ITI calculations in terms of donor strength,
steric bulk and crystallization effects. No analogous actinide compounds were located, likely
13
due to the prevalence of the +4 oxidation state in the early actinides and the scarcity of trans-
plutonium crystallographic data.
Table 2. Inverse trans influence calculated from Eq. 1 for the MBr3(OPcy3)3 (M = Am, Nd,
Pr, Ce, La) series.6
MBr3(OPcy3)3 Am Nd Pr Ce La
Radius (Å)a 0.975 0.983 0.99 1.01 1.032
ITIM–Br 98.8(2) 98.9(2) 98.8(2) 99.0(2) 99.1(1)
ITIM–O 98.2(2) 98.6(3) 98.4(2) 98.6(1) 99.0(3)
a6-Coordinate Shannon Ionic Radius
Electronic Absorption Spectroscopy. The electronic absorption spectroscopy for
AmBr3(OPcy3)3 shows an intense charge transfer band centered at λmax 340 nm (29,411
cm−1
) in addition to the Laporte forbidden 5f → 5f transitions characteristic of AmIII
.65, 66
With few exceptions, the energies of the absorptions are similar to those reported in the low
temperature spectrum of AmBr3 and the recently reported spectrum of (PPh4)3AmCl6.67
The
characteristic 5L6′ excitation reported at 510 nm (19,588 cm
–1) shifted to 508 nm (19,685 cm
–
1), Figure 3. The compound was not fluorescent at room temperature even with long
integration times (≤ 2000 ms) at an excitation wavelength of 365 or 420 nm. CeBr3(OPcy3)3
displays an intense charge transfer band with λmax of 339 nm (29,479 cm–1
). NdBr3(OPcy3)3
reveals, sharp hypersensitive transitions of low intensity between 500–607 nm consistent with
the 4G7/2 and
4G5/2 excitations, similar to the values reported for NdBr3(g) at 1195 °C, while
several of the typical 4f → 4f transitions reported for Nd(ClO4)3(aq) were not observed.68-70
LaBr3(OPcy3)3 and PrBr3(OPcy3)3 gave no UV/vis/NIR peaks between 320–1700 nm. The
former is typical of the 5d04f
0 La
3+ ion, while the latter is unusual for the 4f
2 Pr
3+ ion,
70 this
14
may be due to the pseudo inversion center present in MBr3(OPcy3)3. Though the Pr3+
ion
possesses hypersensitive 3P2 and
1D2 transitions at 444.4 nm (22,500cm
−1) and 588.2 nm
(17,000 cm–1
), respectively, but were not observed through repeated collections, see ESI for
spectra.69, 70
None of the lanthanide compounds were fluorescent.
Figure 3. Solid state UV/vis/NIR of AmBr3(OPcy3)3 at room temperature, with excitation
assignments and photograph of crystals.
Multi-nuclear NMR Spectroscopy. In order to gain more insight into the system, and due to
the convenient spectroscopic handle provided by the 31
P nucleus, 1H,
13C{
1H} and
31P{
1H}
multi nuclear NMR spectra were recorded. Due to radiological constraints and small sample
sizes obtaining NMR spectra on americium samples can be difficult. Exceptions have
included Evans' Method studies,71
a notable solid state MAS study of AmO272
and the recent
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
300 400 500 600 700 800 900 1000 1100 1200
Ab
sorb
an
ce
Wavelength (nm)
7F4′
7F6′
5L6′
5L6′
5D2′
5G2′
5H4′
5G2′
5G4′
15
report of Am(C5Me4H)3.73
Some 31
P{1H} data has been reported previously for other
LnBr3(OPcy3)3 complexes,50
here we seek to add to this data and compare it with its
americium analog. Because of the weak paramagnetism of the 5f 6
Am3+
ion, 1.64 µB,71
a
shorter relaxation time (d1 = 1 sec) was utilized along with several extra scans to obtain a
good signal for AmBr3(OPcy3)3 at a shift of δ 108.89 ppm, Figure 4. To the best of our
knowledge this is the first report of a 31
P NMR signal in an americium complex. The signal is
similar in chemical shift to the 4f 1
CeBr3(OPcy3)3 at δ 109.48 ppm. Both signals are shifted
down field from the diamagnetic LaBr3(OPcy3)3 (δ 60.314 ppm) and the free ligand OPcy3
(δ 50.574 ppm) which was recorded for comparison. The more paramagnetic 4f 2
and 4f 3
PrBr3(OPcy3)3 and NdBr3(OPcy3)3 are significantly shifted further down field (δ 212.4 and
190.2 ppm, respectively) and are significantly broadened (4290 and 1366 Hz, respectively),
Figure 4. Due to the high fluxionality of the cyclohexyl rings the 1H NMR spectra are
complicated and provide limited information. In particular the paramagnetism in
PrBr3(OPcy3)3 and NdBr3(OPcy3)3 give rise to several broad peaks over a range of about 20
ppm, some with widths over 1400 Hz, see ESI for spectra. The 13
C{1H} NMR spectra of
MBr3(OPcy3)3 show several signals and are consistent with a single chemical environment
for the carbons. Due to the small sample size of AmBr3(OPcy3)3 only three of the expected
four signals were observed, with the ipso-carbon likely being too broad and weak to be
observed in this experiment, though a doublet at δ 27.08 ppm with JCP coupling constant of
27 Hz is consistent with the carbon α to the ipso-carbon. For the diamagnetic free ligand and
LaBr3(OPcy3)3 both 1-bond and 2-bond C-P coupling was observed with constants of ca 35
and 27 Hz, respectively. While only the 1-bond C-P coupling was observed in
CeBr3(OPcy3)3 and no coupling was observed in the Pr and Nd compounds, see ESI for
spectra.
16
Figure 4. Stacked 31
P{1H} NMR spectra of MBr3(OPcy3)3 (M = Am, Nd, Pr, Ce, La)
including OPcy3 in CDCl3 at 298-294 K.
Theoretical Analysis
Bonding Analysis. To obtain a deeper understanding of the bonding in MBr3(OPcy3)3, a
Quantum Theory of Atoms In Molecules (QTAIM) analysis was performed to calculate the
concentration of electron density ρ(r), delocalization indices δ(r), and energy densities
[potential, V(r), kinetic, G(r), and total energy densities, H(r)]. All of these metrics are
utilized to determine the degree of covalency exhibited in the bonding interactions. Based on
previous studies where the nature of bonding interactions of f-block complexes has been
shown that bonds are not formally covalent, but rather partially covalent.39, 40, 74
A partial
covalent bond implies positive values for the Laplacian of the electron density, ∇ρ(r), and
negative values for total energy densities, H(r). Here, the term "covalency" refers to the
Am
Nd
Pr
Ce
La
OPcy3
17
metal–ligand interaction needed to experience orbital overlap, which is reflected by the
buildup of electron density [ρ(r)] in the interatomic region. Furthermore, covalency can be
enhanced by a better energy match between the atomic orbital involved, which is reflected by
the delocalization of the electrons in the interatomic region.
Figure 5. QTAIM metrics of the Bond Critical Points (BCPs) derived from the SR-CAS(n,7)
wave functions, (a, Left) Concentration of the electron density, (b, Right) delocalization
indices, and (c) total energy densities. See ESI for exact numbers.
From a general perspective the results herein show that the M–Br bonds displays a
low concentration of electron density in the interatomic region compared to the M–O bonds,
Figure 5a, though similar delocalization indices, Figure 5b, implying that the covalency in
the M–O bonds occur due to increased orbital overlap, whereas the better energy match
between parent metal–ligand orbitals for the M–Br bonds compensate for the lack of electron
density concentration. A more subtle difference is observed in the energy density of the M–O
bonds, particularly the M–O(3) bond where CeBr3(OPcy3)3 most resembles AmBr3(OPcy3)3.
Whereas the M–Br bonds of CeBr3(OPcy3)3 and NdBr3(OPcy3)3 are closer to each other,
18
Figure 6a. The origin of these subtleties resides in the balance between kinetic, G(r), and
potential energy, V(r), densities with respect to the Laplacian of the electron density, ∇ρ(r),
where a more careful treatment can be done when the total electron densities, H(r), is
normalized by the electron density at the Bond Critical Point (BCP). This allows the role of
the kinetic, G(r), and potential energies, V(r), to be isolated from the concentration of
electron density, ρ(r), Figure 6b. When the data are compared, the same trends are observed.
It appears that CeBr3(OPcy3)3 and NdBr3(OPcy3)3 differ from each other in that: the
bonding patterns are independent of the concentration of electron density, ρ(r), i.e. Ce
stabilizes the electrons in the interatomic region similarly to Nd when a more polarizable
ligand is present like Br, while Ce resembles Am when a harder-donor ligand is present, like
OPR3. Moreover, the dominance of potential energy, V(r), over kinetic energy, G(r) is
independent of the electron density, which shows that the covalent contribution in Nd–O(3)
bond is almost negligible, Figure 6b.
Figure 6. Total energy density over the electron density at the BCP derived from a SR-
CAS(7,7) wave function. See ESI for exact numbers.
19
Table 3. Ratio between potential [V(r)] and kinetic [G(r)] energy densities.
|V(r)|/G(r) (kJ mol
−1 Å
−3)
Ce Nd Am
M(1)-Br(1) 1.10 1.10 1.13
M(1)-Br(2) 1.11 1.10 1.14
M(1)-Br(3) 1.09 1.09 1.12
M(1)-O(1) 1.05 1.04 1.04
M(1)-O(2) 1.05 1.04 1.04
M(1)-O(3) 1.03 1.02 1.02
Further characterization of the bonds is provided by the ratio between potential, V(r),
and kinetic, G(r), energy densities, that shows the extent of the polarization of the bond, again
the M–Br bonds are less polarized than the M–O bonds, where Am shows the least polarized
bonds (down to 86% of polarization), Table 3. This agrees with the better energy match
provided by Br− with the lanthanides and actinides, but is most pronounced in the Am
complex.
20
Figure 7. Molecular orbital (MO) energy level diagram for MBr3(OPMe3)3 (M = Am, Ce,
Nd) from a scalar relativistic PBE/TZVP calculation. MO labels correspond to the
predominant shell in the MO, for the MO composition see Tables S2-S4. MO depictions
correspond to the involvement of the semi-core 5/6p orbitals in orbital mixing.
Qualitatively, the ITI correlates with the previous bonding analysis.21
However,
quantitatively, this does not appear to be the case due to the simple shortening of the bond,
which could imply different effects operating simultaneously in the complex. Another way to
corroborate the presence of the ITI is by the inclusion of the 5/6p orbitals in an all-electron
versus a frozen-core calculation .21
Our results show that CeBr3(OPcy3)3 exhibits the highest
amount of stabilization (84.5 kJ/mol) then AmBr3(OPcy3)3 (44.2 kJ/mol), and
NdBr3(OPcy3)3 (35.3 kJ/mol) shows the least amount of stabilization by the inclusion of the
21
5/6p shell, which confirms the presence of the ITI in these systems. However, the energies of
stabilization do not correlate with the trend observed for the ITI percentages coming directly
from the contraction of the bonds in the trans positions. This is not necessarily true for a
system presenting more than one ITI mechanism because they compete within the same
molecule, and therefore become more complicated to analyze. For clarity in the construction
of an MO energy level diagram, the cyclohexyl rings were truncated to methyl groups, e.g.
MBr3(OPMe3)3, Figure 7.75
This mixing is produced with the O 2p and P 3s orbitals,
providing a more delocalized character of the bond and the stronger mixing between 5p
orbitals in Ce is observed, Figure 7.
Another way to show the role of the Ln/An 5/6p orbitals in ITI is to assess the
reduction of the electron repulsion of these semi-core electrons in the complex with respect to
the free-ion. Within ligand field theory (LFT) the one-electron inter-electronic repulsion
integrals are described by the Slater-Condon parameters Fk(nl,nl) (n = shell, l = s,p,d,f) and
the spin-orbit coupling parameter ζnl.76, 77
Previous studies have successfully applied a non-
empirical method to obtain these parameters using a ligand-field DFT (LFDFT) capable of
predicting the electronic structure of lanthanide complexes.45, 78-81
Since the reductions of the
Slater-Condon parameters with respect to the free-ion are related to the central-field and
symmetry-restricted covalency, their evaluation will provide further insight into the nature of
ITI in these complexes.
The reduction of the LF parameters is considerably larger in CeBr3(OPcy3)3
compared to NdBr3(OPcy3)3 and AmBr3(OPcy3)3, whose reductions are similar, Table 4.
These results agree with the stabilization energies obtained between frozen-core to all-
electron calculations, confirming the presence of ITI. This also shows that the sizable
reductions indicate an important covalent component related to the 5/6p orbital involvement
in the interaction between the metal ions and the Br and phosphine oxide ligands.
22
Table 4. Reduction of the Slater-Condon parameters* of the 5/6p semi-core electrons derived
from LF-DFT. Δred refers to the difference between the aquo and MBr3(OPcy)3 (M = Ce, Nd,
Am) complexes.
F2(p,p) (eV) ζ5/6p (eV)
[M(H2O)9]3+
MBr3(OPcy)3 Δred [M(H2O)9]3+
MBr3(OPcy)3 Δred
CeIII
28% 70% 42% 18% 47% 29%
NdIII
21% 43% 22% 15% 28% 13%
AmIII
19% 45% 25% 14% 27% 12%
* See ESI for Slater-Condon parameters
The differences in bonding observed between lanthanides and actinides make the
comparison more complicated due to the involvement of the 5f electrons in the case of
americium, which significantly increases the covalent character of the bond. In this context,
only Ce and Nd could be compared with QTAIM metrics, where delocalization and total
energy densities predict the trend observed in the stabilization energies from the involvement
of the 5p electrons.
Conclusions
The synthesis and characterization of AmBr3(OPcy3)3 has been achieved and shows the same
meridinal coordination geometry as the larger lanthanides. Spectroscopic analysis by single
crystal X-ray diffraction shows that the homo-trans ligands display significantly short bonds
than the hetero-trans ligands. Single crystal UV/vis/NIR spectra show large charge transfer
bands for the Ce and Am complexes and hypersensitive transitions for the Nd and Am
23
analogs due to the pseudo-inversion center. Analysis by 31
P NMR spectroscopy illustrates the
weak paramagnetism of the 5f 6
Am3+
center. Bonding analyses show that the complex
displays a significant inverse trans influence (ITI) with the bonding ligands, though its
mechanism is not directly related to the involvement of the 5/6p electrons. This suggests that
there is an interplay between the involvement of valence electrons that significantly
separates the lanthanides from the actinides. It is surprising that Ce shows the highest amount
of 5p electron involvement in covalency. This is observed by the reduction of the electron–
electron repulsion of the 5p shell compared to the aquo-complex, [Ce(H2O)9]3+
. This study
provides further evidence of ITI in low–valent f-block complexes, and their potential
occurrence in heavier actinides, whose chemistry is dominated by the trivalent oxidation
state. Furthermore, it constitutes a new feature that can be exploited for rational ligand design
in order to achieve selective ligands for separations in nuclear waste treatment.
Conflicts of interest
The authors declare no competing financial interest
Acknowledgements
We thank the support of the U.S. Department of Energy, Office of Science, Office of Basic
Energy Sciences, Heavy Element Chemistry program under Award Number DE-FG02-
13ER16414. The isotopes used in this research were supplied by the U.S. Department of
Energy Isotope Program, managed by the Office of Science for Nuclear Physics. We thank
Benjamin W. Stein and Conrad A. P. Goodwin of Los Alamos National Laboratory for
helpful discussions. We are grateful to Dr. Banghao Chen for his assistance with the NMR
experiments. We thank Jason Johnson and Ashley Gray of Florida State University for
radiological assistance.
24
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29
TOC Image
La
Ce
Pr
Nd
Am
download fileview on ChemRxivAmBrOPcy_ChemRxiv.pdf (1.07 MiB)
S1
Electronic Supporting Information for
Probing the inverse trans influence in americium and lanthanide
tribromide tris(tricyclohexylphosphine oxide)
Cory J. Windorff, Cristian Celis-Barros, Joseph M. Sperling, Bonnie E. Klamm, Noah C.
McKinnon, Thomas E. Albrecht–Schmitt*
Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, RM.
118 DLC, Tallahassee, Florida 32306, USA. E-mail: [email protected];
Table of Contents
PHOTOGRAPHS OF AMERICIUM SYNTHESIS……………………………………………..S2
SOLID STATE UV/VIS/NIR SPECTRA WITH PICTURES OF COMPOUNDS…………………S3
MULTI NUCLEAR NMR SPECTRA……………………………………………………...S4-S14
THEORETICAL CALCULATIONS.………………………………………………………S15-S19
ADDITIONAL ITI CALCULATIONS………………………………………………………S20
CRYSTALLOGRAPHY…………………………………………………………………..S21-S33
REFERENCES…………………………………………………………………………….S34
S2
PHOTOGRAPHS OF AMERICIUM SYNTHESIS
Figure S1. Photograph of AmBr3(OPcy3)3 in iPrOH (left) and 9.0 mg of crystalline material
(Right).
Figure S2. Photograph of AmBr3(OPcy3)3 NMR sample in CDCl3 (left), and additional
photograph of isolated crystals (right).
S3
UV/VIS/NIR SPECTROSCOPY
Figure S3. Solid state UV/vis/NIR spectra of LnBr3(OPcy3)3 [Ln = La (gray), Ce (orange), Pr (blue), Nd (green)] at room temperature.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
325 350 375 400 425 450 475 500 525 550 575 600 625 650 675 700
Ab
sorb
an
ce
Wavelength (nm)
LnBr3(OPcy3)3
LaBr3(OPcy3)3
CeBr3(OPcy3)3
PrBr3(OPcy3)3
NdBr3(OPcy3)3
4G7/2
4G7/2,
4G5/2
S4
MULTI NUCLEAR NMR SPECTROSCOPY
Figure S4. 1H NMR spectrum of AmBr3(OPcy3)3 in CDCl3 at 295 K with expansion of 8 – 0 ppm region, Because the chemical identity of the
peaks is unclear the peaks are integrated relative to one another with the smallest integrated set to 1.
CHCl3
CHCl3
S5
Figure S5. 13
C{1H} NMR spectrum of AmBr3(OPcy3)3 in CDCl3 at 295 K with expansion of 80 – 15 ppm region.
S6
Figure S6. 31
P{1H} NMR spectrum of AmBr3(OPcy3)3 in CDCl3 at 295 K.
S7
Figure S7. Multinuclear NMR spectra of AmBr3(OPcy3)3 at 295 K in CDCl3, 1H (black),
13C{
1H} (red) and
31P{
1H} (green).
S8
Figure S8. Multinuclear NMR spectra of NdBr3(OPcy3)3 at 294 K in CDCl3, 1H (black),
13C{
1H} (red) and
31P{
1H} (green).
S9
Figure S9. Multinuclear NMR spectra of PrBr3(OPcy3)3 at 294 K in CDCl3, 1H (black),
13C{
1H} (red) and
31P{
1H} (green).
S10
Figure S10. Multinuclear NMR spectra of CeBr3(OPcy3)3 at 294 K in CDCl3, 1H (black),
13C{
1H} (red) and
31P{
1H} (green).
S11
Figure S11. Multinuclear NMR spectra of LaBr3(OPcy3)3 at 294 K in CDCl3, 1H (black),
13C{
1H} (red) and
31P{
1H} (green).
S12
Figure S12. Multinuclear NMR spectra of OPcy3 at 298 K in CDCl3, 1H (black),
13C{
1H} (red) and
31P{
1H} (green).
S13
Figure S13. Stacked 13
C{1H} NMR spectra of MBr3(OPcy3)3 (M = Am, Nd, Pr, Ce, La) including OPcy3 in CDCl3 at 298-294 K.
Am
Nd
Pr
Ce
La
OPcy3
S14
Figure S14. Stacked 31
P{1H} NMR spectra of MBr3(OPcy3)3 (M = Am, Nd, Pr, Ce, La) including OPcy3 in CDCl3 at 298-294 K.
Am
Nd
Pr
Ce
La
OPcy3
S15
THEORETICAL CALCULATIONS
Table S1. QTAIM metrics derived from SR-CAS wave functions for MBr3(OPcy)3 (M = Ce, Nd, Am) complexes. With the following
definitions: ρ(r) – electron density, (eÅ−3
), δ(r) – delocalization indices, V(r) – potential energy density (kJmol−1
Å−3
), G(r) – kinetic energy
density (kJmol−1
Å−3
), and H(r) – total energy density (kJmol−1
Å−3
). H(r)/ ρ(r) represents a "normalized" energy density per electron (kJmol−1
).
ρ(r) δ(r) V(r) G(r)
Ce Nd Am Ce Nd Am Ce Nd Am Ce Nd Am
M(1)-Br(1) 0.2571 0.2693 0.2834 0.3215 0.3172 0.3515 −556.2 −600.1 −666.8 505.3 547.4 589.6
M(1)-Br(2) 0.2618 0.2645 0.2895 0.3209 0.3173 0.3519 −570.3 −586.0 −686.1 515.9 535.2 603.6
M(1)-Br(3) 0.2463 0.2517 0.2686 0.3140 0.3087 0.3399 −522.9 −547.4 −619.4 479.0 503.6 551.0
M(1)-O(1) 0.4090 0.4252 0.4387 0.2950 0.2925 0.3094 −1366.9 −1484.4 −1595.0 1305.4 1426.5 1531.8
M(1)-O(2) 0.4076 0.4184 0.4468 0.2926 0.2862 0.3170 −1354.6 −1444.1 −1642.3 1291.4 1389.7 1573.9
M(1)-O(3) 0.3732 0.3779 0.3982 0.2682 0.2597 0.2834 −1207.2 −1259.8 −1391.4 1175.6 1240.5 1359.8
|V(r)|/G(r) H(r) H(r)/ρ(r)
Ce Nd Am Ce Nd Am Ce Nd Am
M(1)-Br(1) 1.10 1.10 1.13 −50.9 −52.6 −77.2 −197.9 −195.5 −272.4
M(1)-Br(2) 1.11 1.10 1.14 −54.4 −50.9 −82.5 −207.7 −192.3 −284.8
M(1)-Br(3) 1.09 1.09 1.12 −43.9 −43.9 −68.4 −178.1 −174.3 −254.8
M(1)-O(1) 1.05 1.04 1.04 −61.4 −57.9 −63.2 −150.2 −136.2 −144.0
M(1)-O(2) 1.05 1.04 1.04 −63.2 −54.4 −68.4 −155.0 −130.0 −153.2
M(1)-O(3) 1.03 1.02 1.02 −31.6 −19.3 −31.6 −84.6 −51.1 −79.3
S16
Table S2. Molecular orbital (MO) composition of AmBr3(OPMe3)3 for the following orbital
populations: Am – 6p, 5f, 6d; O – 2s, 2p; Br – 4s, 4p; P – 3s, 3p. Percentages in bold
represent the main contribution to the MO. Energies given are relative to the first O 2s MO.
E(eV) Molecular orbital composition
Am 6p Am 5f Am 6d O 2s O 2p Br 4s Br 4p P 3s P 3p
0.0 14%
66%
8% 4%
0.1 6%
69% 3%
11% 5%
0.4
73% 3%
11% 5%
2.6 96%
1%
2.7 89%
1% 3%
2%
2.8 78%
5% 7%
5%
8.1
100%
8.3
100%
8.4 2%
97%
14.7
31%
14.8
42%
10%
15.4
5% 40%
5%
17.4
3%
64%
17.5
2%
68%
17.7
3%
61%
17.7
68%
17.8
66%
17.9
66%
18.9
4%
84%
19.5
3% 3%
87%
19.7
2% 3%
91%
19.8
6% 3%
88%
19.9
3%
93%
20.0
2%
92%
20.0
4%
91%
20.0
2%
92%
20.3
2%
97%
22.2
100%
22.3
95%
1%
22.3
100%
22.3
95%
1%
22.5
89%
4%
22.5
89%
6%
22.5
91%
S17
Table S3. Molecular orbital (MO) composition of CeBr3(OPMe3)3 for the following orbital
populations: Ce – 5p, 4f, 5d; O – 2s, 2p; Br – 4s, 4p; P – 3s, 3p. Percentages in bold represent
the main contribution to the MO. Energies given are relative to the first O 2s MO.
E(eV) Molecular orbital composition
Ce 5p Ce 4f Ce 5d O 2s O 2p Br 4s Br 4p P 3s P 3p
0.0 2%
71% 4%
11% 6%
0.1 4%
72% 2%
10% 6%
0.3
72% 1%
12% 6%
4.6 68%
7%
9%
4.7 70%
4% 1%
7%
4.8 93%
5%
8.2
100%
8.4 2%
96%
8.5 5%
94%
14.7
37%
14.8
4% 44%
4%
15.5
23%
17.3
3%
64%
1%
17.4
2%
68%
1%
17.5
3%
67%
17.6
69%
17.7
69%
17.7
70%
19.1
2%
85%
19.6
1% 4%
89%
19.8
6%
90%
19.9
2%
93%
19.9 2%
94%
20.0
3%
1%
93%
20.0
100%
20.1
1%
95%
20.4
100%
23.5
100%
23.6
100%
23.6
100%
23.6
100%
23.7
89%
2%
23.7
94%
3%
23.7
94%
S18
Table S4. Molecular orbital (MO) composition of NdBr3(OPMe3)3 for the following orbital
populations: Nd – 5p, 4f, 5d; O – 2s, 2p; Br – 4s, 4p; P – 3s, 3p. Percentages in bold
represent the main contribution to the MO. Energies given are relative to the first O 2s MO.
E (eV) Molecular orbital composition
Nd 5p Nd 4f Nd 5d O 2s O 2p Br 4s Br 4p P 3s P 3p
0.0 4%
71% 3%
10% 5%
0.0 6%
70% 1%
10% 4%
0.3
72% 4%
12% 8%
3.6 82%
6%
5%
3.6 89%
3% 1%
3%
3.7 95%
3%
8.2
1%
99%
8.4
97%
8.4 3%
97%
14.8
4%
36%
14.8
4% 42%
4%
15.5 3%
6% 46%
6%
17.3
3%
64%
1%
17.5
2%
69%
1%
17.6
3%
65%
17.7
69%
17.7
68%
17.8
70%
19.1
6%
85%
19.6
2% 4%
88%
19.8
5%
92%
19.9
4% 2%
92%
19.9 2%
94%
20.0
4%
2%
93%
20.0
2%
94%
20.0
95%
20.4
98%
22.3
100%
22.3
100%
22.4
100%
22.4
100%
22.5
93%
2%
22.5
93%
22.5
93%
4%
S19
Table S5. Slater-Condon parameters of the 5/6p semi-core electrons derived from LF-DFT
for the free-ions, [M(H2O)9]3+
, and MBr3(OPcy)3 complexes (M = Ce, Nd, Am).
F2(p,p) (eV) ζ5/6p (eV)
Free-ion [M(H2O)9]3+
MBr3(OPcy)3 Free-ion [M(H2O)9]3+
MBr3(OPcy)3
CeIII
7.715 5.557 2.320 1.774 1.454 0.938
NdIII
7.970 6.259 4.520 2.063 1.754 1.492
AmIII
7.583 6.112 4.207 5.818 4.985 4.259
Further Electronic Structure Discussion.
The ground and low-lying excited states in AmBr3(OPcy3)3 were calculated to gain a
better understanding what role the ligands play in bonding to americium. For comparison, the
same calculations were performed on the cerium and neodymium complexes to determine the
ground state multiplet splitting. The ground multiplet splitting in CeBr3(OPcy3)3 corresponds
to an unusual J = 5/2 for a Ce(III) complex, and is reflected in the spitting of the low-lying
Kramer's doublets (KDs) at 831.5 cm−1
. The closest reported value is 1036.6 cm−1
for
{(C8H6(SiMe3)2]2Ce}−.1 A simple calculation of the free-Ce(III) ion shows a splitting of 2
cm−1
, which highlights the role of the phosphine oxide ligand.. When the same analysis is
performed on NdBr3(OPcy3)3 a ground state J = 9/2 multiplet that spans an energy window of
413.8 cm−1
is calculated and is comparable to the ~495 cm−1
experimentally determined value
for Nd2O3 crystals.2 Unfortunately, this analysis cannot be performed for AmBr3(OPcy3)3
because there is no splitting due to the J = 0 ground state. However, it is clear that the quasi-
octahedral environment provides a strong ligand field environment capable of modifying the
electronic properties of these complexes.
S20
ITI COMPARISONS AND CALCULATIONS OF LITERATURE COMPOUNDS
Table S6. ITI Calculations of Newly Reported and Previously Reported LnBr3(OPcy3)3
Compounds.a
Lab La
3 Ce
b Pr
b Pr
3 Nd
b Nd
3 Gd
3 Ho
3
Radiusc 1.032 1.032 1.01 0.99 0.99 0.983 0.983 0.938 0.901
ITIM–Br 99.1(1) 99.7(1) 99.0(2) 98.9(2) 98.7(5) 98.9(2) 98.7(3) 98.7(3) 98.7(3)
ITIM–O 99.0(3) 99.0(3) 98.56(8) 98.4(2) 98.3(2) 98.6(3) 98.7(2) 99.0(1) 98.5(3)
aGiven with calculated standard error in parentheses
bThis work
c6-Coordinate Shannon Ionic
Radius
Table S7. ITI Calculations of LnI3(Et2O)3 Compounds.4,a,b
Ce Pr Nd Sm Gd Tb
Radius 1.01 0.99 0.983 0.958 0.938 0.923
ITIM–I 101.21(2) 101.22(2) 99.87[7] 101.16(2) 100.96(2) 101.00(2)
ITIM–O 95.8(1) 95.4(2) 97.6[7] 95.1(2) 96.1(1) 95.9(2)
aGiven with calculated standard errors in parentheses and propagated error in square brackets
b6-Coordinate Shannon Ionic Radius
5
Table S8. ITI Calculations of LnCl3(HMPA)3 Compounds.a,b
Pr6 Dy
7 Yb
8
Radius 0.99 0.912 0.868
ITIM–Cl 100.8(1) 100.4(1) 100.3(1)
ITIM–O 100.1(1) 98.92(2) 100.3(1)
aGiven with calculated standard errors in parentheses
b6-Coordinate Shannon Ionic Radius
5
Table S9. ITI Calculations of YbX3(THF)3 Compounds.a,b
Cl9 Br
10 I
11
ITIM–X 100.7(1) 101.6[1] 101.34[2]
ITIM–O 96.9(5) 96.8[5] 97.3[3]
aGiven with calculated standard errors in parentheses and propagated error in square brackets
b6-Coordinate Shannon Ionic Radius
5
S21
CRYSTALLOGRAPHY
Table S10. Summary of Crystallographic Collections for MBr3(OPcy3)3.
Compound Am La Ce Pr Nd
Empirical
Formula
C54H99O3P3
Br3Am
C54H99O3P3
Br3La
C54H99O3P3
Br3Ce
C54H99O3.5P3
Br3Pr
C54H99O3P3
Br3Nd
Temperature
(K) 120(2) 130(2) 120(2) 120(2) 120(2)
Crystal
System Orthorhombic Orthorhombic Orthorhombic Orthorhombic Orthorhombic
Space Group Pca21 Pca21 Pca21 Pca21 Pca21
a (Å) 28.768(9) 28.879(2) 28.920(5) 28.716(1) 28.706(1)
b (Å) 11.456(4) 11.4223(7) 11.434(2) 11.4126(4) 11.4228(4)
c (Å) 18.185(6) 18.208(1) 18.209(3) 18.1299(8) 18.1359(7)
(°) 90 90 90 90 90
(°) 90 90 90 90 90
(°) 90 90 90 90 90
Volume (Å3) 5993(3) 6006.3(6) 6021(2) 5941.5(4) 5946.8(4)
Z 4 4 4 4 4
calcd
(Mg/m3)
1.521 1.402 1.400 1.420 1.422
(mm−1
) 3.398 2.824 2.864 2.956 3.007
R1a
(I > 2.0 0.0399 0.0348 0.0353 0.0317 0.0405
wR2
(all data) 0.0858 0.0620 0.0726 0.0617 0.0777
BASF 0.02978 0.01767 0.03608 0.00891 -0.00554
aDefinitions: wR2 = {[w(Fo
2−Fc
2)2] / [w(Fo
2)2]}
1/2 R1 = ||Fo|−|Fc|| / |Fo|
Goof = S = {[w(Fo2−Fc
2)2] / (n−p)}
1/2 where n is the number of reflections and p is the total
number of parameters refined.
S22
Table S11. Bond lengths [Å] and angles [°] for AmBr3(OPcy3)3.
_____________________________________________________
Am(1)-Br(1) 2.882(1)
Am(1)-Br(2) 2.870(1)
Am(1)-Br(3) 2.912(1)
Am(1)-O(1) 2.312(7)
Am(1)-O(2) 2.302(7)
Am(1)-O(3) 2.349(6)
Br(1)-Am(1)-Br(3) 95.60(5)
Br(2)-Am(1)-Br(1) 172.74(3)
Br(2)-Am(1)-Br(3) 91.54(5)
O(1)-Am(1)-Br(1) 89.05(18)
O(1)-Am(1)-Br(2) 89.73(19)
O(1)-Am(1)-Br(3) 89.44(18)
O(1)-Am(1)-O(3) 90.2(3)
O(2)-Am(1)-Br(1) 90.44(18)
O(2)-Am(1)-Br(2) 91.00(18)
O(2)-Am(1)-Br(3) 88.81(18)
O(2)-Am(1)-O(1) 178.1(2)
O(2)-Am(1)-O(3) 91.6(3)
O(3)-Am(1)-Br(1) 87.6(2)
O(3)-Am(1)-Br(2) 85.2(2)
O(3)-Am(1)-Br(3) 176.7(2)
_____________________________________________________________
Table S12. Bond lengths [Å] and angles [°] for LaBr3(OPcy3)3.
_____________________________________________________
La(1)-Br(1) 2.9365(7)
La(1)-Br(2) 2.9425(7)
La(1)-Br(3) 2.9649(5)
La(1)-O(1) 2.351(4)
La(1)-O(2) 2.363(4)
La(1)-O(3) 2.382(3)
Br(1)-La(1)-Br(2) 172.59(2)
Br(1)-La(1)-Br(3) 91.39(3)
Br(2)-La(1)-Br(3) 95.84(3)
O(1)-La(1)-Br(1) 91.08(10)
O(1)-La(1)-Br(2) 90.73(10)
O(1)-La(1)-Br(3) 88.27(9)
O(1)-La(1)-O(2) 178.16(13)
O(1)-La(1)-O(3) 91.97(14)
O(2)-La(1)-Br(1) 89.62(10)
O(2)-La(1)-Br(2) 88.79(10)
O(2)-La(1)-Br(3) 90.01(10)
O(2)-La(1)-O(3) 89.78(15)
O(3)-La(1)-Br(1) 85.23(12)
O(3)-La(1)-Br(2) 87.53(12)
O(3)-La(1)-Br(3) 176.61(12)
_____________________________________________________________
Table S13. Bond lengths [Å] and angles [°] for CeBr3(OPcy3)3.
_____________________________________________________
Ce(1)-Br(1) 2.9268(8)
Ce(1)-Br(2) 2.9166(8)
Ce(1)-Br(3) 2.9504(8)
Ce(1)-O(1) 2.332(4)
Ce(1)-O(2) 2.336(4)
Ce(1)-O(3) 2.368(4)
Br(1)-Ce(1)-Br(3) 95.47(3)
Br(2)-Ce(1)-Br(1) 172.78(2)
Br(2)-Ce(1)-Br(3) 91.61(3)
O(1)-Ce(1)-Br(1) 90.50(10)
O(1)-Ce(1)-Br(2) 91.16(10)
S23
O(1)-Ce(1)-Br(3) 88.33(11)
O(1)-Ce(1)-O(2) 177.66(14)
O(1)-Ce(1)-O(3) 92.37(16)
O(2)-Ce(1)-Br(1) 89.08(11)
O(2)-Ce(1)-Br(2) 89.55(11)
O(2)-Ce(1)-Br(3) 89.42(11)
O(2)-Ce(1)-O(3) 89.91(16)
O(3)-Ce(1)-Br(1) 87.42(13)
O(3)-Ce(1)-Br(2) 85.48(13)
O(3)-Ce(1)-Br(3) 177.02(12)
_____________________________________________________________
Table S14. Bond lengths [Å] and angles [°] for PrBr3(OPcy3)3.
_____________________________________________________
Pr(1)-Br(1) 2.8781(7)
Pr(1)-Br(2) 2.8894(7)
Pr(1)-Br(3) 2.9145(5)
Pr(1)-O(1) 2.294(4)
Pr(1)-O(2) 2.302(4)
Pr(1)-O(3) 2.336(3)
Br(1)-Pr(1)-Br(2) 173.18(2)
Br(1)-Pr(1)-Br(3) 91.37(3)
Br(2)-Pr(1)-Br(3) 95.32(2)
O(1)-Pr(1)-Br(1) 90.95(10)
O(1)-Pr(1)-Br(2) 90.53(10)
O(1)-Pr(1)-Br(3) 88.55(10)
O(1)-Pr(1)-O(2) 177.63(13)
O(1)-Pr(1)-O(3) 92.17(15)
O(2)-Pr(1)-Br(1) 89.61(10)
O(2)-Pr(1)-Br(2) 89.18(10)
O(2)-Pr(1)-Br(3) 89.13(10)
O(2)-Pr(1)-O(3) 90.17(15)
O(3)-Pr(1)-Br(1) 85.72(12)
O(3)-Pr(1)-Br(2) 87.57(12)
O(3)-Pr(1)-Br(3) 177.02(11)
_____________________________________________________________
Table S15. Bond lengths [Å] and angles [°] for NdBr3(OPcy3)3.
_____________________________________________________
Nd(1)-Br(1) 2.8796(8)
Nd(1)-Br(2) 2.8908(9)
Nd(1)-Br(3) 2.9168(6)
Nd(1)-O(1) 2.297(5)
Nd(1)-O(2) 2.309(5)
Nd(1)-O(3) 2.336(4)
Br(1)-Nd(1)-Br(2) 173.15(3)
Br(1)-Nd(1)-Br(3) 91.38(3)
Br(2)-Nd(1)-Br(3) 95.34(3)
O(1)-Nd(1)-Br(1) 91.04(13)
O(1)-Nd(1)-Br(2) 90.45(13)
O(1)-Nd(1)-Br(3) 88.59(12)
O(1)-Nd(1)-O(2) 177.70(16)
O(1)-Nd(1)-O(3) 92.20(19)
O(2)-Nd(1)-Br(1) 89.81(14)
O(2)-Nd(1)-Br(2) 88.95(13)
O(2)-Nd(1)-Br(3) 89.26(13)
O(2)-Nd(1)-O(3) 89.99(19)
O(3)-Nd(1)-Br(1) 85.78(15)
O(3)-Nd(1)-Br(2) 87.49(15)
O(3)-Nd(1)-Br(3) 177.06(14)
_____________________________________________________________
S24
X-ray Data Collection, Structure Solution and Refinement for AmBr3(OPcy3)3.
An amber crystal of approximate dimensions 0.06 x 0.12 x 0.196 mm was mounted
on a nylon loop and transferred to a Bruker D8 Quest diffractometer. The APEX312
program
package was used to determine the unit-cell parameters and for data collection (17 sec/frame
scan time for a calculated scan of diffraction data and a detector distance of 41 mm). The raw
frame data was processed using SAINT13
and SADABS14
to yield the reflection data file.
Subsequent calculations were carried out using the SHELXTL15
or OLEX216
program. The
diffraction symmetry was mmm and the systematic absences were consistent with the
orthorhombic space groups Pbcm and Pca21. It was later determined that space group Pca21
was correct.
The initial structure was solved by direct methods using Pu in place of Am, since Am
is not recognized by APEX3. The structure was refined on F2 by full-matrix least-squares
techniques using Am, the scattering factors for which were taken from the International
Tables for Crystallography Volume C.17
The analytical scattering factors for neutral atoms
were used throughout the analysis.17
Hydrogen atoms were included using a riding model.
The absolute structure was assigned by refinement of the Flack parameter.18
Based on
the Flack parameter, the data was refined as a 2-component twin with BASF = 0.02978. The
compound was found to isomorphous with its lanthanide analogs: Pr (BUGRIG),3 Nd
(BUGROM),3 Gd (BUGRUS),
3 Ho
(ROVNUN),3 which are all
reported as a hemi-hydrate, which
was not located in the Fourier map
for Am.
Figure S15. Thermal ellipsoid plot of AmBr3(OPcy3)3 drawn at the 50% probability level
with hydrogen atoms omitted for clarity.
Am1 O1 O2
O3
P1 P2
P3
Br1
Br2
Br3
S25
Table S16. Crystal data and structure refinement for AmBr3(OPcy3)3.
Identification code cjw84 (Cory Windorff)
Empirical formula C54H99O3P3Br3Am
Formula weight 1371.97
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pca21
Unit cell dimensions a = 28.768(9) Å = 90°.
b = 11.456(4) Å = 90°.
c = 18.185(6) Å = 90°.
Volume 5993(3) Å3
Z 4
Density (calculated) 1.521 Mg/m3
Absorption coefficient 3.398 mm−1
F(000) 2768
Crystal color clear yellow
Crystal size 0.196 x 0.12 x 0.06 mm3
Theta range for data collection 2.217 to 27.521°
Index ranges −35 ≤ h ≤ 37, −14 ≤ k ≤ 14, −23 ≤ l ≤ 20
Reflections collected 70455
Independent reflections 12088 [R(int) = 0.0751]
Completeness to theta = 25.242° 99.9 %
Absorption correction Semi–empirical from equivalents
Max. and min. transmission 0.0949 and 0.0640
Refinement method Full–matrix least–squares on F2
Data / restraints / parameters 12088 / 1 / 578
Goodness-of-fit on F2 1.081
Final R indices [I>2sigma(I) = 9606 data] R1 = 0.0399, wR2 = 0.0787
R indices (all data, 0.77 Å) R1 = 0.0606, wR2 = 0.0858
Absolute structure parameter 0.004(7)
Largest diff. peak and hole 2.033 and −2.008 e.Å−3
BASF 0.02978
S26
X-ray Data Collection, Structure Solution and Refinement for LaBr3(OPcy3)3.
A colorless crystal of approximate dimensions 0.153 x 0.157 x 0.267mm was
mounted on a nylon loop and transferred to a Bruker D8 Quest diffractometer. The APEX312
program package was used to determine the unit-cell parameters and for data collection (15
sec/frame scan time for a calculated scan of diffraction data and a detector distance of 33
mm). The raw frame data was processed using SAINT13
and SADABS14
to yield the
reflection data file. Subsequent calculations were carried out using the SHELXTL15
or
OLEX216
program. The diffraction symmetry was mmm and the systematic absences were
consistent with the orthorhombic space groups Pbcm and Pca21. It was later determined that
space group Pca21 was correct.
The structure was solved by direct methods and refined on F2 by full-matrix least-
squares techniques. The analytical scattering factors for neutral atoms were used throughout
the analysis.17
Hydrogen atoms were included using a riding model.
The absolute structure was assigned by refinement of the Flack parameter.18
Based on
the Flack parameter, the data was refined as a 2-component twin with BASF = 0.01767. The
compound was not isomorphous with its previous report (BUGREC),3 and was found to
isomorphous with its other lanthanide analogs: Pr (BUGRIG),3 Nd (BUGROM),
3 Gd
(BUGRUS),3 and Ho (ROVNUN),
3 which are all reported as a hemi-hydrate, which was not
located in the Fourier map for La.
Figure S16. Thermal ellipsoid plot of LaBr3(OPcy3)3 drawn at the 50% probability level
with hydrogen atoms omitted for clarity.
La1 O1 O2
O3
P1 P2
P3
Br1
Br2
Br3
S27
Table S17. Crystal data and structure refinement for LaBr3(OPcy3)3.
Identification code cjw86 (Cory Windorff)
Empirical formula C54H99O3P3Br3La
Formula weight 1267.88
Temperature 130(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pca21
Unit cell dimensions a = 28.8790(16) Å = 90°.
b = 11.4223(7) Å = 90°.
c = 18.2083(10) Å = 90°.
Volume 6006.3(6) Å3
Z 4
Density (calculated) 1.402 Mg/m3
Absorption coefficient 2.824 mm−1
F(000) 2616
Crystal color clear colorless
Crystal size 0.267 x 0.157 x 0.153 mm3
Theta range for data collection 2.220 to 27.545°
Index ranges −37 ≤ h ≤ 37, −14 ≤ k ≤ 14, −22 ≤ l ≤ 23
Reflections collected 109745
Independent reflections 13561 [R(int) = 0.0669]
Completeness to theta = 25.500° 99.9 %
Absorption correction Semi–empirical from equivalents
Max. and min. transmission 0.7456 and 0.6638
Refinement method Full–matrix least–squares on F2
Data / restraints / parameters 13561 / 1 / 578
Goodness-of-fit on F2 1.092
Final R indices [I>2sigma(I) = 11489 data] R1 = 0.0348, wR2 = 0.0566
R indices (all data, 0.77 Å) R1 = 0.0510, wR2 = 0.0620
Absolute structure parameter 0.018(9)
Largest diff. peak and hole 0.757 and −0.569 e.Å−3
BASF 0.01767
S28
X-ray Data Collection, Structure Solution and Refinement for CeBr3(OPcy3)3.
An orange crystal of approximate dimensions 0.123 x 0.156 x 0.268 mm was mounted
on a nylon loop and transferred to a Bruker D8 Quest diffractometer. The APEX312
program
package was used to determine the unit-cell parameters and for data collection (60 sec/frame
scan time for a calculated scan of diffraction data and a detector distance of 42 mm). The raw
frame data was processed using SAINT13
and SADABS14
to yield the reflection data file.
Subsequent calculations were carried out using the SHELXTL15
or OLEX216
program. The
diffraction symmetry was mmm and the systematic absences were consistent with the
orthorhombic space groups Pbcm and Pca21. It was later determined that space group Pca21
was correct.
The structure was solved by direct methods and refined on F2 by full-matrix least-
squares techniques. The analytical scattering factors for neutral atoms were used throughout
the analysis.17
Hydrogen atoms were included using a riding model.
The absolute structure was assigned by refinement of the Flack parameter.18
Based on
the Flack parameter, the data was refined as a 2-component twin with BASF = 0.03608. The
compound is isomorphous with its other lanthanide analogs: Pr (BUGRIG),3 Nd
(BUGROM),3 Gd (BUGRUS),
3 and Ho (ROVNUN),
3 which are all reported as a hemi-
hydrate, which was not located in the Fourier map for Ce.
Figure S17. Thermal ellipsoid plot of CeBr3(OPcy3)3 drawn at the 50% probability level
with hydrogen atoms omitted for clarity.
Ce1 O1 O2
O3
P1 P2
P3
Br1
Br2
Br3
S29
Table S18. Crystal data and structure refinement for CeBr3(OPcy3)3.
Identification code cjw61 (Cory Windorff)
Empirical formula C54H99O3P3Br3Ce
Formula weight 1269.09
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pca21
Unit cell dimensions a = 28.920(5) Å = 90°.
b = 11.434(2) Å = 90°.
c = 18.209(3) Å = 90°.
Volume 6021.2(18) Å3
Z 4
Density (calculated) 1.400 Mg/m3
Absorption coefficient 2.864 mm−1
F(000) 2620
Crystal color clear orange
Crystal size 0.268 x 0.156 x 0.123 mm3
Theta range for data collection 2.218 to 27.511°
Index ranges −37 ≤ h ≤ 37, −14 ≤ k ≤ 14, −23 ≤ l ≤ 23
Reflections collected 122286
Independent reflections 13805 [R(int) = 0.0685]
Completeness to theta = 25.242° 99.9 %
Absorption correction Semi–empirical from equivalents
Max. and min. transmission 0.7456 and 0.6448
Refinement method Full–matrix least–squares on F2
Data / restraints / parameters 13805 / 1 / 578
Goodness-of-fit on F2 1.057
Final R indices [I>2sigma(I) = 11775 data] R1 = 0.0353, wR2 = 0.0664
R indices (all data, 0.77 Å) R1 = 0.0499, wR2 = 0.0726
Absolute structure parameter −0.001(4)
Largest diff. peak and hole 0.956 and −0.784 e.Å−3
BASF 0.03608
S30
X-ray Data Collection, Structure Solution and Refinement for PrBr3(OPcy3)3.
A colorless crystal of approximate dimensions 0.315 x 0.205 x 0.188 mm was
mounted on a nylon loop and transferred to a Bruker D8 Quest diffractometer. The APEX312
program package was used to determine the unit-cell parameters and for data collection (15
sec/frame scan time for a calculated scan of diffraction data at a detector distance of 35 mm).
The raw frame data was processed using SAINT13
and SADABS14
to yield the reflection data
file. Subsequent calculations were carried out using the SHELXTL15
or OLEX216
program.
The diffraction symmetry was mmm and the systematic absences were consistent with the
orthorhombic space groups Pbcm and Pca21. It was later determined that space group Pca21
was correct.
The structure was solved by direct methods and refined on F2 by full-matrix least-
squares techniques. The analytical scattering factors for neutral atoms were used throughout
the analysis.17
Hydrogen atoms were included using a riding model.
The absolute structure was assigned by refinement of the Flack parameter.18
Based on
the Flack parameter, the data was refined as a 2-component twin with BASF = 0.00891. The
compound is a redetermination of the previously data (BUGRIG),3 and is isomorphous with
its other lanthanide analogs: Nd
(BUGROM),3 Gd (BUGRUS),
3
and Ho (ROVNUN).3
Figure S18. Thermal ellipsoid plot of PrBr3(OPcy3)3 drawn at the 50% probability level
with hydrogen atoms (and lattice solvent) omitted for clarity.
Pr1 O1 O2
O3
P1 P2
P3
Br1
Br2
Br3
S31
Table S19. Crystal data and structure refinement for PrBr3(OPcy3)3.
Identification code cjw94 (Cory Windorff)
Empirical formula C54H99O3P3Br3Pr
Formula weight 1269.88
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pca21
Unit cell dimensions a = 28.716(1) Å α = 90°.
b = 11.4126(4) Å β = 90°.
c = 18.1299(8) Å γ = 90°.
Volume 5941.5(4) Å3
Z 4
Density (calculated) 1.420 Mg/m3
Absorption coefficient 2.956 mm−1
F(000) 2624
Crystal color clear colorless
Crystal size 0.315 x 0.205 x 0.188 mm3
Theta range for data collection 2.225 to 27.551°
Index ranges −37 ≤ h ≤ 37, −14 ≤ k ≤ 14, −23 ≤ l ≤ 23
Reflections collected 106432
Independent reflections 13677 [R(int) = 0.0613]
Completeness to theta = 25.500° 99.9 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.7456 and 0.6775
Refinement method Full-matrix least-squares on F2
Data / restraints / parameters 13677 / 1 / 578
Goodness-of-fit on F2 1.055
Final R indices [I>2sigma(I) = 11537 data] R1 = 0.0317, wR2 = 0.0556
R indices (all data, 0.77 Å) R1 = 0.0481, wR2 = 0.0617
Absolute structure parameter 0.009(9)
Largest diff. peak and hole 0.990 and −0.720 e.Å−3
BASF 0.00891
S32
X-ray Data Collection, Structure Solution and Refinement for NdBr3(OPcy3)3.
A colorless crystal of approximate dimensions 0.224 x 0.202 x 0.170 mm was
mounted on a nylon loop and transferred to a Bruker D8 Quest diffractometer. The APEX312
program package was used to determine the unit-cell parameters and for data collection (10
sec/frame scan time for a hemisphere of diffraction data with a scan width of 0.5° and a
detector distance of 35 mm). The raw frame data was processed using SAINT13
and
SADABS14
to yield the reflection data file. Subsequent calculations were carried out using
the SHELXTL15
or OLEX216
program. The diffraction symmetry was mmm and the
systematic absences were consistent with the orthorhombic space groups Pbcm and Pca21. It
was later determined that space group Pca21 was correct.
The structure was solved by direct methods and refined on F2 by full-matrix least-
squares techniques. The analytical scattering factors for neutral atoms were used throughout
the analysis.17
Hydrogen atoms were included using a riding model.
The absolute structure was assigned by refinement of the Flack parameter.18
Based on
the Flack parameter, the data was refined as a 2-component twin with BASF = -0.00554. The
structure is known (BUGROM)3 and was re-determined. The compound is isomorphous with
its other lanthanide analogs: Pr (BUGRIG),3 Gd (BUGRUS),
3 and Ho (ROVNUN),
3 which
are all reported as a hemi-
hydrate, which was not
located in the Fourier map
for Nd.
Figure S19. Thermal ellipsoid plot of NdBr3(OPcy3)3 drawn at the 50% probability level
with hydrogen atoms omitted for clarity.
Nd1 O1 O2
O3
P1 P2
P3
Br1
Br2
Br3
S33
Table S20. Crystal data and structure refinement for NdBr3(OPcy3)3.
Identification code cjw93 (Cory Windorff)
Empirical formula C54H99O3P3Br3Nd
Formula weight 1273.21
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pca21
Unit cell dimensions a = 28.7074(14) Å = 90°.
b = 11.4137(6) Å = 90°.
c = 18.1291(10) Å = 90°.
Volume 5946.8(4) Å3
Z 4
Density (calculated) 1.422 Mg/m3
Absorption coefficient 3.007 mm−1
F(000) 2628
Crystal color clear colorless
Crystal size 0.224 x 0.202 x 0.170 mm3
Theta range for data collection 2.223 to 27.557°
Index ranges −37 ≤ h ≤ 37, −14 ≤ k ≤ 14, −22 ≤ l ≤ 23
Reflections collected 106339
Independent reflections 13649 [R(int) = 0.0874]
Completeness to theta = 25.500° 99.9 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.7456 and 0.6784
Refinement method Full-matrix least-squares on F2
Data / restraints / parameters 13649 / 1 / 578
Goodness-of-fit on F2 1.037
Final R indices [I>2sigma(I) = 11307 data] R1 = 0.0405, wR2 = 0.0680
R indices (all data, 0.77 Å) R1 = 0.0608, wR2 = 0.0777
Absolute structure parameter -0.006(12)
Largest diff. peak and hole 1.021 and −1.569 e.Å−3
BASF -0.00554
S34
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