Inorganic Chemistry Communications 11 (2008) 1057–1059

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Inorganic Chemistry Communications

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Synthesis, crystal structure and characterizations of a novel lanthanideoxalatophosphonate with a 3D open-framework structure[Gd2{HO3PCH2NHCH2(CH2CH2OPO2)}(C2O4)2.5(H2O)2] � 5H2O

Yan Zhao, Jing Li, Zhen-Gang Sun *, Jing Zhang, Yan-Yu Zhu, Xin Lu, Lei Liu, Na ZhangInstitute of Chemistry for Functionalized Materials, Faculty of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 25 April 2008Accepted 25 May 2008Available online 1 July 2008

Keywords:Metal phosphonatesCrystal structureHydrothermal synthesisGadolinium(III)

1387-7003/$ - see front matter � 2008 Elsevier B.V. Adoi:10.1016/j.inoche.2008.05.030

* Corresponding author. Tel.: +86 411 82156568; faE-mail address: szg188@163.com (Z.-G. Sun).

A novel lanthanide oxalatophosphonate, [Gd2{HO3PCH2NHCH2(CH2CH2OPO2)}(C2O4)2.5(H2O)2] � 5H2O 1has been synthesized by hydrothermal reaction at 140 �C and structurally characterized by single-crystalX-ray diffraction as well as with infrared spectroscopy, elemental analysis and thermogravimetric anal-ysis. The interconnection of gadolinium(I) ions by bridging H2L– anions leads to a 3D open-frameworkstructure with channels along the a-axis. The channel is formed by 44-membered rings composed of sixgadolinium(I) ions and six H2L– anions. The chelating and bridging oxalates are found on the surface ofthe channels extending along the a direction.

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At present the design and construction of new functional inor-ganic–organic hybrid materials based on metal phosphonates hasbeen extensively studied. This is not only due to their structuraldiversities but also for their potential or practical application inthe area of catalysis, ion exchange, proton conductivity, intercala-tion chemistry, photochemistry, and materials chemistry [1–4].Recently, many research activities have focused on the synthesisof inorganic–organic hybrid compounds by incorporating organicligands in the structures of metal phosphonates. The direct use oftwo types of ligands in the preparation, such as a phosphonic acidand a carboxylic acid, has been found to be another effective meth-od for the exploration of hybrid open-framework. The rapid devel-opment in the rational design and synthesis of metalphosphonates, by introducing the second organic ligand, has pro-vided several compounds with interesting architectures and possi-ble functionalities [5–8].

Among these studies, the oxalate moiety, C2O42�, was found to

be a good candidate and has been successfully incorporated intophosphonate frameworks with transition metals and main groupelements [9–11]. Although some progress has been made in theconstruction of metal oxalatophosphonate as mentioned above,less progress has been achieved in the synthesis of lanthanide oxa-latophosphonates [12,13]. Recently, a series of metal phospho-nates, using phosphonic acids with amine, hydroxyl, andcarboxylate groups as ligands, have been isolated in our laboratory[14–17]. As an extension of our work, a research program has also

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been initiated in the synthesis of new materials with open-frame-work structures by introducing a second ligand in the structures ofmetal phosphonates. In the paper, a novel lanthanide oxa-latophosphonate with a 3D open-framework structure,[Gd2{HO3PCH2NHCH2(CH2CH2OPO2)}(C2O4)2.5(H2O)2] � 5H2O 1 hasbeen synthesized by hydrothermal technique, using organophos-phonic acid, H2O3PCH2NCH2(CH2CH2OPO2H) (H3L) as ligand(Scheme 1), and oxalate as the second ligand [18]. The compoundstructure was characterized by X-ray single-crystal diffraction [19],infrared spectroscopy, elemental and thermogravimetric analysis.

X-ray single-crystal diffraction reveals that compound 1 crystal-lizes in monoclinic space group P2(1)/n. The asymmetric unit isshown in Fig. 1 (see Tables 1 and 2).

As shown in Fig. 1, Gd1 atom has a distorted dodecahedral coor-dination geometry. Six of the eight coordination positions are filledwith six oxygen atoms from three oxalate anions, and the remain-ing sites are occupied by two phosphonate oxygen atoms from twoseparate H2L– ligands. Gd2 is also eight coordinated by four oxygenatoms from three oxalate anions, two phosphonate oxygen atomsfrom two separate H2L– ligands and two oxygen atoms from watermolecules. The Gd–O distances are in the range of 2.285(7)–2.486(7) Å. Each oxalate anion is tetradentate and forms twoGd–O–C–C–O five-membered chelating rings. The H2L– ligand actsas a tetradentate ligand and connects four Gd(III) ions through fourphosphonate oxygen atoms. One phosphonate oxygen atom (O5) isprotonated, so does its amine group, which is due to the zwitter-ionic behavior of the aminophosphonic acid [20].

The interconnection of the gadolinium(III) ions by chelating andbridging oxalate anions lead to a 3D network of [Gd2(C2O4)2.5]+

CH2

CH2

CH2

CH2

O

N

PO3H2

PO

OH

Scheme 1. The schematic structure of H2O3PCH2NCH2(CH2CH2OPO2H) (H3L).

Fig. 1. A fragment of the structure in compound 1 with atom labeling scheme (30%probability). All H atoms and lattice water molecules are omitted for clarity.Symmetry codes: (A) x – 1/2, –y + 5/2, z + 1/2; (B) –x + 2, –y + 2, –z + 1; (C) x + 1/2, –y + 5/2, z + 1/2; (D) –x + 1, –y + 2, –z + 1.

Fig. 3. A ball and stick and polyhedral representation of the framework structure ofcompound 1 in the bc plane.

Table 1Crystal data and structure refinement for compound 1

Compound 1Formula C9H24Gd2NO23P2

Fw 890.73Crystal system MonoclinicSpace group P2(1)/nColor ColorlessCrystal size, mm 0.07 � 0.03 � 0.02a, Å 8.6839(12)b, Å 31.729(4)c, Å 9.2922(13)a, � 90

1058 Y. Zhao et al. / Inorganic Chemistry Communications 11 (2008) 1057–1059

with one-dimensional channel system along the c-axis (Fig. 2). Thechannel system is assembled by 40-atom rings (18.6 Å � 5.4 Å,estimated by measuring the distances between the centers ofopposite atoms), which consist of ten Gd, ten C and twenty Oatoms. The 3D network of [Gd2(C2O4)2.5]+ are interconnected byphosphonate groups via sharing gadolinium(I) ions to form a 3Dopen-framework structure with channels along the a-axis (Fig.3). The channel is formed by 44-membered rings composed ofsix gadolinium(I) ions and six H2L– anions. The chelating andbridging oxalates are found on the surface of the channels extend-ing along the a direction.

The IR spectrum [21] of compound 1 was recorded in the regionfrom 4000 to 400 cm–1 (see Fig. S4). A very strong absorption bandaround 3422 cm�1 corresponds to the OH stretching vibrations ofthe title compound. A strong band at 1627 cm�1 is observed whichis shifted at least 90 cm�1 from the expected value of uncoordi-nated carboxylic acid (v(CO) typically around 1725–1700 cm�1)

Fig. 2. View of a 3D network of [Gd2(C2O4)2.5]+ for compound 1 down the c-axis.

b, � 98.514(2)c, � 90V, Å3 2532.1(6)Z 4Dcacl, g cm3 2.337T, K 295(2)Reflections collected 13705Independent reflections 4981 (Rint = 0.0667)Theta range 2.31 to 26.01l, mm�1 5.419F (000) 1708R, Rw [I>2r (I)] 0.0500, 0.1144R, Rw (all data) 0.0814, 0.1303Goodness-of-fit 1.004

R1 = R(|F0|–|FC|)/R|F0|; wR2 = [Rw(|F0|–|FC|)2/RwF02]1/2.

[22]. This large shift is due to the carboxylate function coordinatedto the metal. The medium absorption band around 1321 cm�1 isprobably due to the bending vibration of CH. The set of bands be-tween 1200 and 900 cm�1 are due to stretching vibrations of thetetrahedral CPO3 groups [23]. Additional medium bands at low en-

Table 2Selected bond lengths (Å) and angles (�) for compound 1

Compound 1Gd(1)–O(1) 2.313(6) Gd(2)–O(4) 2.285(7)Gd(1)–O(3)#1 2.328(7) Gd(2)–O(6)#4 2.305(9)Gd(1)–O(8)#2 2.377(7) Gd(2)–O(16)#3 2.425(8)Gd(1)–O(9) 2.405(7) Gd(2)–O(13) 2.435(7)Gd(1)–O(7) 2.410(7) Gd(2)–O(18) 2.438(9)Gd(1)–O(14)#3 2.424(7) Gd(2)–O(15) 2.449(8)Gd(1)–O(10)#2 2.424(7) Gd(2)–O(11) 2.452(8)Gd(1)–O(12)#3 2.486(7) Gd(2)–O(17) 2.452(10)P(1)–O(1) 1.482(7) P(2)–O(4) 1.481(8)P(1)–O(3) 1.490(7) P(2)–O(6) 1.491(9)P(1)–O(2) 1.586(8) P(2)–O(5) 1.555(9)P(1)–C(1) 1.804(10) P(2)–C(2) 1.821(11)O(1)–Gd(1)–O(3)#1 152.6(2) O(4)–Gd(2)–O(6)#4 101.3(3)O(1)–Gd(1)–O(8)#2 94.3(3) O(4)–Gd(2)–O(16)#3 80.5(3)O(3)#1–Gd(1)–O(8)#2 90.6(3) O(6)#4–Gd(2)–O(16)#3 140.2(3)O(1)–Gd(1)–O(9) 87.1(3) O(4)–Gd(2)–O(13) 143.6(3)O(3)#1–Gd(1)–O(9) 100.9(3) O(6)#4–Gd(2)–O(13) 78.5(3)O(8)#2–Gd(1)–O(9) 152.0(2) O(16)#3–Gd(2)–O(13) 122.9(3)O(1)–Gd(1)–O(7) 82.5(3) O(4)–Gd(2)–O(18) 73.8(3)O(3)#1–Gd(1)–O(7) 76.7(3) O(6)#4–Gd(2)–O(18) 79.1(4)O(8)#2–Gd(1)–O(7) 140.4(2) O(16)#3–Gd(2)–O(18) 137.2(3)O(9)–Gd(1)–O(7) 67.6(2) O(13)–Gd(2)–O(18) 2.071(3)O(1)–Gd(1)–O(14)#3 137.2(2) O(4)–Gd(2)–O(15) 83.3(3)O(3)#1–Gd(1)–O(14)#3 70.2(2) O(6)#4–Gd(2)–O(15) 73.5(3)O(8)#2–Gd(1)–O(14)#3 83.5(2) O(16)#3–Gd(2)–O(15) 67.2(3)O(9)–Gd(1)–O(14)#3 76.7(3) O(13)–Gd(2)–O(15) 129.7(3)O(7)–Gd(1)–O(14)#3 124.6(3) O(18)–Gd(2)–O(15) 139.9(3)O(1)–Gd(1)–O(10)#2 77.2(2) O(4)–Gd(2)–O(11) 149.3(3)O(3)#1–Gd(1)–O(10)#2 79.8(2) O(6)#4–Gd(2)–O(11) 91.6(3)O(8)#2–Gd(1)–O(10)#2 67.5(2) O(16)#3–Gd(2)–O(11) 71.9(3)O(9)–Gd(1)–O(10)#2 139.4(2) O(13)–Gd(2)–O(11) 66.1(2)O(7)–Gd(1)–O(10)#2 73.3(2) O(18)–Gd(2)–O(11) 136.5(3)O(14)#3–Gd(1)–O(10)#2 137.9(2) O(15)–Gd(2)–O(11) 73.7(3)O(1)–Gd(1)–O(12)#3 72.2(2) O(4)–Gd(2)–O(17) 91.4(4)O(3)#1–Gd(1)–O(12)#3 135.0(2) O(6)#4–Gd(2)–O(17) 146.1(3)O(8)#2–Gd(1)–O(12)#3 76.3(2) O(16)#3–Gd(2)–O(17) 72.6(3)O(9)–Gd(1)–O(12)#3 77.6(2) O(13)–Gd(2)–O(17) 72.9(3)O(7)–Gd(1)–O(12)#3 137.7(2) O(18)–Gd(2)–O(17) 74.4(4)O(14)#3–Gd(1)–O(12)#3 65.7(2) O(15)–Gd(2)–O(17) 139.7(3)O(10)#2–Gd(1)–O(12)#3 130.0(2) O(11)–Gd(2)–O(17) 93.1(3)

Symmetry transformations used to generate equivalent atoms: #1 –x + 1, –y + 1, –z + 1; #2 –x + 2, –y + 1, –z + 1; #3 –x + 2, –y + 2, –z + 1; #4 x, y + 1, z; #5 –x + 1, –y, –z + 1.

Y. Zhao et al. / Inorganic Chemistry Communications 11 (2008) 1057–1059 1059

ergy (between 800 and 400 cm�1) are found, these bands are prob-ably due to bending vibrations of the tetrahedral CPO3 groups.

Thermogravimetric analysis [24] diagram of compound 1 re-veals three main steps of weight losses (see Fig. S5). The first stepcorresponds to the loss of lattice water molecules. The weight lossbegins at 50 �C and is completed at 175 �C. The observed weightloss of 10.1% is very close to the calculated value (10.6%). The sec-ond step occurs in the range of 200 � 500 �C, which can be attrib-uted to the loss of the coordinated water molecules and oxalateanions. The third weight loss corresponds to the decompositionof organophosphonate groups. The total weight loss of 43.6% isclose to the calculated value (43.4%) if the final product is assumedto be GdPO4.

In conclusion, a novel lanthanide oxalatophosphonate with a 3Dopen-framework structure, [Gd2{HO3PCH2NHCH2(CH2CH2OPO2)}(-C2O4)2.5(H2O)2] � 5H2O 1 has been synthesized by hydrothermaltechnique, using organophosphonic acid, H2O3PCH2NCH2(CH2-

CH2OPO2H) as ligand, and oxalate as the second ligand. The inter-connection of gadolinium(I) ions by bridging H2L– anions leads toa 3D open-framework structure with channels along the a-axis.The channel is formed by 44-membered rings composed of six gad-olinium(I) ions and six H2L– anions. The chelating and bridgingoxalates are found on the surface of the channels extending alongthe a direction.

Acknowledgment

This research was supported by Grants from the Natural ScienceFoundation of Liaoning Province of China (20062140).

Appendix A. Supplementary material

CCDC 670984 contains the supplementary crystallographic datafor this paper. These data can be obtained free of charge from TheCambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this articlecan be found, in the online version, at doi:10.1016/j.inoche.2008.05.030.

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Zhang, Inorg. Chem. Commun. 10 (2007) 1109.[18] The compound 1 was synthesized by hydrothermal reactions. A mixture of

0.19 g (0.5 mmol) GdCl3 � 6H2O, 0.07 g (0.25 mmol) H3L, 0.08 g (2 mmol)NaOH, 0.25 g (2 mmol) H2C2O4 � 2H2O and 10.0 ml deionized water wassealed into a 20 ml Teflon-lined stainless steel autoclave, and then heatedat 140 �C for 96 h. After the mixture was cooled slowly to roomtemperature, colorless block crystals were obtained in ca. 49.8% yieldbased on Gd. The initial and final pH values of solution were 4.0 and 5.0,respectively. Anal. Calcd. for C9H24Gd2NO23P2: C, 12.12; H, 2.69; N, 1.57; P,6.96; Gd, 35.36. Found: C, 12.21; H, 2.63; N, 1.51; P, 6.87; Gd, 35.45%.

[19] Crystal structure analysis: The data were collected at a temperature of293 ± 2 K on a Bruker Smart APEX a X-diffractometer equipped with graphitemonochromated Mo Ka radiation (k = 0.71073 Å). An empirical absorptioncorrection was applied using the SADABS program with Tmax = 0.8901 andTmin = 0.6899. The structure was solved in the space group P2(1)/n by directmethod and refined by the full-matrix least-squares fitting on F2 usingSHELXS–97 [25]. All non-hydrogen atoms were treated anisotropically.Hydrogen atoms of organic ligands were generated geometrically, fixedisotropic thermal parameters, and included in the structure factorcalculations. Crystal data for 1: C9H24Gd2NO23P2, M = 890.73, monoclinic,P2(1)/n, a = 8.6839(12) Å, b = 31.729(4) Å, c = 9.2922(13) Å, b = 98.514(2)�,V = 2532.1(6) Å3, Z = 4, Dc = 2.337 g cm–3, l = 5.419 mm–1. Data werecollected on a single crystal with dimensions 0.07 � 0.03 � 0.02 mm3. 13705reflections were measured with x-scans, in the range of 2.31� 6 h 6 26.01�(�10 6 h 6 9, �33 6 k 6 39, –11 6 l 6 11), 4981 independent reflections(Rint = 0.0667). Final R1 = 0.0500, wR2 = 0.1144 [I > 2r (I)], and the goodness-of-fit on F2 is 1.004.

[20] D.M. Poojary, B.L. Zhang, A. Clearfield, Chem. Mater. 11 (1999) 421.[21] The infrared spectrum was recorded from a KBr pellet by use of a Bruker AXS

TENSOR-27 FT–IR spectrometer in the range 4000–400 cm–1.[22] A. Cabeza, M.A.G. Aranda, S. Bruque, J. Mater. Chem. 8 (1998) 2479.[23] A. Cabeza, X. Ouyang, C.V.K. Sharma, M.A.G. Aranda, S. Bruque, A. Clearfield,

Inorg. Chem. 41 (2002) 2325.[24] TG analysis was performed on a Perkin–Elmer Pyris Diamond TG–DTA thermal

analyses system in static air with a heating rate of 10 K min–1 from 50 to900 �C.

[25] G.M. Sheldrick, SHELXS–97, Program for X-ray Crystal Structure Solution andRefinement, University of Göttingen, Germany, 1997.