A Novel 1D Chain Compound Constructed from Alternating Wells-Dawson Polyanions and Mixed-Valence Hexacopper Phosphate Cations Hongxun Yang, Jingxiang Lin, Jiutong Chen, Xiandong Zhu, Shuiying Gao, and Rong Cao*
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 8 2623–2625
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fujian, Fuzhou 350002, P. R. China, and Graduate School, Chinese Academy of Sciences, Beijing 100039, P. R. China ReceiVed May 6, 2008; ReVised Manuscript ReceiVed June 12, 2008
ABSTRACT: A novel compound constructed from alternating Wells-Dawson POMs building blocks and mixed-valence hexacopper phosphate cations was isolated and the compound is a 1D infinitely linear chain exhibiting an -ACACAC- type structure.
Polyoxometalates (POMs) have been investigated for a long time because of their distinctive topological structures and versatile applications in catalysis, medicine, biology, electrochromism, and material science.1 Polyoxometalate frameworks, being nanosized discrete metal-oxygen cluster anions and attractive inorganic building blocks of nanostructured materials, can act as effective ligands to coordinate various transition metals because of its high electronic density.2 One promising approach for the design and construction of the POMs hybrid materials is to build connections between the surface oxygen atoms of POMs and organic ligands or metal coordination compounds. Many hybrid compounds based on Keggin type polyoxometalate clusters and transition metal coordination compounds have been hydrothermally synthesized.3 However, the composite materials constructed from Wells-Dawson POMs anions with 1D or 2D network have been rarely reported.4 On the other hand, transition metal phosphate/phosphonate compounds have also been received much attention in recent years, owing to its potential applications of cation exchangers, sorption, catalyst support, sensors, and nonlinear optics.3h,i,5 Hence, assembling the transition metal phosphate compounds/clusters into POM building blocks may lead to hybrid compounds with interesting structures, topologies, and properties. Herein, we will report the synthesis and characterizations of a novel compound, [CuII4CuI2(PO4)2(H2O)2(bpy)6](H3O)2[R-P2W18O62] (bpy ) 2,2′-bipyridine) 1 constructed from Wells-Dawson polyanions and hexacopper phosphate cations. Compound 1 was obtained by the hydrothermal reaction of Na2WO4 · 2H2O, H3PO4, CuCl2 · 2H2O, 2,2′-bipyridine, and H2O at 160 °C for 5 days.6 Single crystal X-ray analysis shows that compound 1 consists of an unusual mixed-valence hexacopper phosphate cation [CuII4CuI2(bpy)6(H2O)2(PO4)2]4+, a polyoxoanion [P2W18O62]6- and two lattice water molecules7 (Figure 1). The [P2W18O62]6- polyoxoanion exhibits R-Wells-Dawson structure and contains two PW9 halves linked by almost linear W-Ob-W bonds. The W8-O23A-W6A bond angel is ∼163.3° (see the Supporting Information, Table S1), which is ∼5° smaller than the β-Wells-Dawson anions.8 The [R-P2W18O62]6- polyoxoanion is built from edge- and corner-sharing octahedral, the W-O band distances are in the range 1.70-1.72 and 1.68-1.74 Å for terminal oxygen atoms, 1.89-1.93 and 1.88-1.95 Å for µ2-bridging oxygen atoms, and 2.36-2.40 Å for µ3-bridging oxygen atoms, respectively; P-O distances are in the range 1.53-1.58 Å (see the Supporting Information, Table S1). The results show that the structure of [R-P2W18O62]6- is in good agreement with both the Dawson and D’Amour structures of Wells-Dawson anions.9 * Corresponding author. Tel: 86 591 83796710. Fax: 8659183714946. E-mail: rcao@fjirsm. ac. cn.
The most striking structural feature of compound 1 is the presence of the mixed-valence hexacopper cluster [CuII4CuI2 (PO4)2(H2O)2(bpy)6]4+(Figure 2). The cluster contains two PO4 tetrahedral, six Cu atoms, and six 2,2′-bipyridine ligands. All four oxygen atoms of each PO43- participate in coordination, two of them function as µ2-bridge linking two Cu atoms, and each of the other two coordinates to one Cu atom. Thus, six copper atoms are linked by two PO4 tetrahedral to form a unique hexacopper octahedron cluster with Cu2, Cu3, Cu2A, and Cu3A atoms being in the equatorial plane and Cu1 and Cu1A occupying the apexes. The valence state of the two apex Cu atoms (Cu1 and Cu1A) is +1 and each of them is four-coordinated by two nitrogen atoms from 2,2′-bipyridine ligand, an oxygen atom from phosphate group, and a terminal water ligand. The valence state of the four equatorial Cu atoms (Cu2, Cu2A, Cu3, and Cu3A) is +2 and each of them is five coordinated in square pyramid geometry: Cu2 is coordinated by two nitrogen atoms from 2,2′-bipy ligand, two oxygen atoms from two different phosphate groups and one terminal oxygen atom located in the “cap” site of the [R-P2W18O62]6- Wells-Dawson cluster; Cu3 is coordinated by two nitrogen atoms from 2,2′-bipy ligand, and three oxygen atoms from two different PO4 tetrahedra. The presence of Cu+ comes from the reduction of Cu2+ by 2,2′bipyridine during the formation of the compound and is confirmed by bond valence sum calculation and XPS spectrum (see the Supporting Information, Figure S2). Bond valence sum calculation shows that the value for the calculated oxidation state of Cu1, Cu2, and Cu3 is 1.293, 2.187, and 2.070, respectively, which is consistent with the formula of compound 1.10 The hexacopper cluster cation and the [R-P2W18O62]6- anion alternately connect each other through the terminal oxygen atom(O18) located in the “cap” site of the Dawson type anion (Figure 2) to form 1D infinitely linear chain exhibiting -ACACAC- type structure(Figure 3). It should be noted that the noncoordination lattice water molecules, which lie in the gap of the anion [R-P2W18O62]6- and hexacopper cation [CuII4CuI2 (bpy) 6(H2O) 2(PO4)2]4+, have not interaction with the other atoms of compound 1 by hydrogen-bonding or weak interaction. Because the distances between the noncoordination water molecules and its adjacent atoms [O1w-O36 3.279 Å, O1w-Cu1 2.824(1) Å and O1w-O1 3.508(2) Å] (see the Supporting Information, Table S2) are out of the hydrogen-bonding distance or weak interaction. The two lattice water molecules are protonated for the requirement of charge balance. The magnetic behavior of compound 1 was investigated between 2 K and 300K, and the thermal evolution of the magnetic molar susceptibility χm and the χmT value are shown in Figure 4. The χmT curve displays a continuous decrease upon cooling from 300 K (χmT ) 1.68 cm3 mol-1 K) to 2 K (χmT ) 0.47 cm3 mol-1 K). The magnetic data of compound 1 obeys Curie-Weiss equation
10.1021/cg800471x CCC: $40.75 2008 American Chemical Society Published on Web 07/10/2008
2624 Crystal Growth & Design, Vol. 8, No. 8, 2008
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Figure 2. Detail of the hexacopper phosphate cation sandwiched between two [R-P2W18O62]6- polyanions in the chain. Thick black bonds show the predominant Cu-Cu interactions within the clusters. All the carbon atoms of the 2,2′-bpy ligands, hydrogen atoms and lattice water molecules are omitted for clarity. Relevant bond distances (Å) and angles (deg) are as follows: Cu2-Cu3A 3.359(2), Cu2-Cu3 3.554(2), Cu2-Cu2A 5.017(2), Cu3-Cu3A 4.760(2), Cu1-Cu3A 5.263(2), Cu1-Cu2A 5.425(3), Cu1-Cu2 5.636(2), Cu1-Cu3 5.678(4); Cu3ACu2-Cu3 86.983 (2), Cu2-Cu3-Cu2A 93.017(2).
Figure 3. View of the 1D chain of compound 1. All the hydrogen atoms and lattice water molecules are omitted for clarity. Blue, pink, and yellow polyhedral show the [CuN2O3] and [CuN2O2], [PO4], [WO6] units, respectively.
Figure 1. (a) View of the [P2W18O62]6- polyoxoainon in compound 1. (b) Coordination environments of copper in compound 1. The hydrogen atoms and the lattice water molecules are omitted for clarity.
with the Curie constant C ) 1.90 cm3 mol-1 K and the Weiss constant θ ) -52.67 K in the range between 20 and 300 K. This behavior suggests the existence of strong antiferromagnetic interactions between the hexacopper clusters.11 The χmT value at 300 K is slightly higher than the calculated χmT value of 1.67 cm3 mol-1 K for four uncoupled spins Cu2+(S ) 1/2), and the two Cu+(S ) 0) located at the apexes of the hexacopper cation have not contribution to the magnetic molar susceptibility. The temperaturedependent magnetic susceptibility of compound 1 also confirms the mixed-valence hexacopper phosphate cation. The XPS measurement for compound 1 (see the Supporting Information, Figure S2) shows the spectrum of 1 in the Cu2p region with a peak at 932.57 eV, which is ascribed to Cu+ ion, and the satellite peak (943.82 eV) can be used as a fingerprint for identifying the presence of Cu2+.12 The XPS estimation for the valence state values is in good agreement with the results from the bond valence sum calculation and magnetic study. In summary, an interesting 1D chain composite compound, [CuII4CuI2(PO4)2(H2O)2(bpy)6](H3O)2[R-P2W18O62] (bpy ) 2,2′-
Figure 4. Thermal evolution of the magnetic susceptibility and χmT product for compound 1. Inset shows a plot of χm-1 versus T for compound 1 between 20 and 300 K.
bipyridine) 1, has been synthesized hydrothermally and structurally characterized. Although many composite compounds have been constructed by POMs, to the best of our knowledge, compound 1 is the first example constructed from mixed-valence hexacopperphosphate cluster and R-Dawson POM building blocks. The work
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Crystal Growth & Design, Vol. 8, No. 8, 2008 2625
may provide a new strategy for construction of POM-based composite materials and further studies are underway.
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Acknowledgment. This work was financially supported by the 973 Program (2006CB932903), NSFC (20521101 and 20731005), NSF of Fujian Province (E0520003, and 2006F3134), Fujian Key Laboratory of Nanomaterials (2006L2005), “The Distinguished Oversea Scholar Project”, “One Hundred Talent Project”, and key project from CAS. H.Y. thanks Prof. Jiutong Chen for the helpful discussion on the structure of compound 1 and Dr. Yougui Huang for help on magnetic properties. Supporting Information Available: Selected bond distances and angles, selected distances between the noncoordination lattice water molecules and their adjacent atoms, XPS spectrum, IR spectrum, and XPRD patterns. These materials are available free of charge via the Internet at http://pubs.acs.org.
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Inorg. Chem. 2003, 42, 1158. (d) Kortz, U.; Vaissermann, J.; Thouvenot, R.; Gouzerh, P. Inorg. Chem. 2003, 42, 1135. Synthesis of 1: A mixture of Na2WO4 · 2H2O (0.341 g), CuCl2 · 2H2O (0.087 g), H3PO4 (0.5 mL), 2,2′-bpy (0.04g), and H2O (15 mL) was mixed and stirred for 30 min, and the pH was adjusted to 2.5-3.0 with 1 M NaOH solute. The resulting suspension was transferred to a Teflon-lined autoclave (25 mL) and kept at 160 °C for 5 days. After slow cooling to room temperature for 2 days, blue prism crystals of 1 were obtained by filtering, washing with distilled water, and drying in desiccators at ambient temperature. The yield was ca. 43% based on W. Elemental anal. Calcd (%) for C60H56Cu6N12O74P4W18 (5943.59): W, 55.68; Cu, 6.41; P, 2.08; C, 12.12; H, 0.95; N, 2.83. Found: W, 55.59; Cu, 6.29; P, 2.21; C, 12.22; H, 1.06; N, 2.93. The experimental and simulated XPRD patterns of compound 1 fit well (see the Supporting Information, Figure S3), indicating the purity of the product. The infrared spectrum of 1 exhibits four characteristic asymmetric vibrations for the Wells-Dawson structure, namely, P-Oa 1093 cm-1, W--Ot 957 cm-1, corner-sharing W-Oc-W 903 cm-1, edge-sharing W-Oe-W 794 cm-1, respectively. And the 1150-1700 cm-1 region is indicative of the organic ligand 2,2′-bpy (see the Supporting Information, Figure S4). Crystal data for 1: C60H56Cu6N12O74P4W18, M ) 5943.3, monoclinic, space group C2/c, a ) 23.2312(16) Å, b ) 17. 1912(10) Å, c ) 28.154(2) Å, β ) 102.225(3)°, V ) 10989.0(3) Å3, Z ) 4; F(000) ) 10 600, 38 193 reflections in h (-30/30), k (-20/22), l (-33/36), measured in the range 2.07° e θ e 27.48°, 12515 independent reflections, Rint ) 0.0540, 850 parameters, 24 restraints, R1 ) 0.0505 and wR2 ) 0.1340 [I > 2σ(I)], R1 ) 0.0591 and wR2 ) 0.1401 (all data), GOF ) 1.131. The data were collected on a Mercury CCD (2 × 2 bin mode) diffractometer with graphite monochromated Mo-KR radiation (λ ) 0.71073 Å) at 20 °C. Empirical from equivalents were made from ψ-scan data using the program SHELXTL 97. The structure of compound 1 was solved by the direct methods (Wingx32, SIR92), and successive Fourier difference syntheses. All the atoms were refined with anisotropic thermal parameters except the atoms of the disorder 2,2′-bpy and all hydrogen atoms. The 2,2′-bipyridine molecule coordinated with the Cu1 is disordered over a center of inversion and was refined as a rigid hexagon having 1.39 Å (see the Supporting Information, Figure S1). CCDC-680366 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html. Lopez, X.; Bo, C.; Poblet, J. M. Inorg. Chem. 2003, 42, 2634–2638. (a) Ho¨ldscher, M.; Englert, U.; Zibrowlius, B.; Ho¨ldscher, W. F. Angew. Chem., Int. Ed. 1994, 33, 2491. (b) Dawson, B. Acta Crystallogr. 1953, 6, 113. (c) D’Amour, V. H. Acta Crystallogr., Sect. B 1976, 32, 729. (a) Brese, N. E.; O, Keefe, M. Acta. Crystallogr., Sect. B 1991, 47, 192. (b) Thorp, H. H. Inorg. Chem. 1998, 37, 5690. (c) Westmorland, T. D.; Wilcox, D. E.; Baldwin, M. J.; Mims, W. B.; Solomon, E. I. J. Am. Chem. Soc. 1989, 111, 6106. (d) Zhang, X. M.; Tong, M. L.; Gong, M. L.; Lee, H. K.; Luo, L.; Li, K. F.; Tong, Y. X.; Chen; X. M., Chem.sEur. J. 2002, 8, 3187. (e) Wang, J. P.; Ma, P. T.; Niu, J. Y. Inorg. Chem. Commun. 2006, 9, 1049. (a) Jones, L. F.; Kilner, C. A.; Miranda, M. P.; Wolowska, J.; Halcrow, M. A. Angew. Chem., Int. Ed. 2007, 46, 4073. (b) Gonza´-P´; erez, J. M.; Alarco´n-Payer, C. A.; Castineiras, A.; Pivetta, T.; Lezama, L.; Choquesillo-Lazarte, D.; Crisponi, G.; Niclo´s-Gutie´rrez, J. N. Inorg. Chem. 2006, 45, 877. (a) Vernon, G. A.; Stucky, G.; Carlson, T. A. Inorg. Chem. 1976, 15, 278. (b) Jiang, Y. J.; Gao, Q. M. Mater. Lett. 2007, 61, 2212.
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