Solvothermal Assembly of a Series of OrganicâInorganic Hybrid

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Solvothermal Assembly of a Series of OrganicInorganic Hybrid Materials Constructed from Keggin Polyoxometalate Clusters and Copper(I)Organic Frameworks Hai-Yan Liu,†,‡ Hua Wu,† Jin Yang,*,† Ying-Ying Liu,† Jian-Fang Ma,*,† and Hong-Ye Bai† †

Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast Normal University, Changchun 130024, People's Republic of China ‡ Department of Chemistry and Pharmaceutical Engineering, Suihua University, Suihua 152061, People's Republic of China

bS Supporting Information ABSTRACT: Seven polyoxometalate (POM) hybrid materials based on Keggin polyanion building blocks and copper(I)organic frameworks with pyrazine derivatives, namely, [CuI4(2Et,3Me-Pyr)5(SiW12O40)] (1), [CuI4(2,6-Pyr)4(SiW12O40)] (2), [CuI4(2,5-Pyr)4(SiW12O40)(H2O)2] (3), [CuI4(2,3,5,6-Pyr)4(SiW12O40)](H2O) (4), [CuI4(2,5-Pyr)4(PMoVI11MoVO40)] 3 1.5H2O (5), [CuI3(2,3,5-Pyr)4(PMo12O40)] 3 H2O (6), and [CuI4(2Et,3Me-Pyr)5(PMoVI11MoVO40)] (7), where 2Et,3Me-Pyr = 2-ethyl-3-methylpyrazine, 2,6-Pyr = 2,6-dimethylpyrazine, 2,5-Pyr = 2,5-dimethylpyrazine, 2,3,5-Pyr = 2,3,5-trimethylpyrazine, and 2,3,5,6-Pyr = 2,3,5,6tetramethylpyrazine, have been synthesized under solvothermal conditions. In 1 and 7, polyanions link CuIorganic sheets to generate 3D (3,4)-connected frameworks. In 2, the polyanion bridges CuIorganic chains to yield a 3D (3,4,6)-connected framework. Both 3 and 4 exhibit 2D double layer structures. In 5, the Keggin polyanion bridges the CuIPyr chains to form an infinite 3D (3,4)-connected framework. In 6, CuI cations are bridged by the 2,3,5-Pyr and Keggin polyanions to generate a novel 2D (8,3) sheet. The roles of the pyrazine derivatives and the Keggin polyanions in the formation of the POM-based MOFs have been discussed.

’ INTRODUCTION The design and assembly of organicinorganic hybrid compounds are currently of great interest because of their structural diversities and potential applications as functional materials.1 Polyoxometalates (POMs), as one kind of important metal oxide cluster with nanosizes, abundant topologies, and great potential applications in catalysis, ion exchange, sorption, magnetism, electrical conductivity, and photochemistry, have been employed as inorganic building blocks for the construction of organic inorganic hybrid materials with various transition metal complexes.24 Among the different types of POMs, the Keggin type polyanions, because of its diverse electronic, magnetic, photochemical, and catalytic properties, have been regarded as an important inorganic building unit to construct POM-supported metal organic frameworks (MOFs).5 To date, remarkable hybrid compounds based on Keggin heteropolyanions have been reported, but in contrast, examples containing high dimensional structures POMsupported MOFs are still less.5 Most of them are connected through noncovalent interactions (van der Waals contacts, hydrogen-bonding, and/or ionic interactions) between the POMs and the transition metal organic units. It can be seen that the rational design and assembly of POM-based coordination polymers, especially covalent connection, remains an arduous task for POM chemists. According to the previous literature, we have noticed that CuI cation, as a d10 transition metal, possesses high affinity for N and O donors and flexible coordination numbers of 24 in covalent r 2011 American Chemical Society

complexes. So far, a few 3D POM-supported MOFs containing CuI cations, displaying fascinating architectures, have been reported.5h,6 From the reported documents, we found that the CuII cations are usually reduced to CuI cations under solvothermal conditions, with the result that the CuI cations could be introduced into the reaction system.7 Therefore, in the present work, the solvothermal synthetic approach is selected to construct POM-supported MOFs.8 Several previous reports by Long and co-workers have indicated that pyrazine and its derivatives are excellent candidates for the construction of Keggin-supported MOFs.6d,e It has been demonstrated that the steric hindrance of the organic ligand plays an important role in the formation of POM-supported MOFs. However, systematic studies to probe the influence of organic ligands on the structures of POM-supported MOFs are still scarce.6 In this work, five different pyrazine derivatives were selected as organic ligands to construct novel POM-supported MOFs and further explore their effects on the structures of POM-supported MOFs (Scheme 1). Here, seven Keggin-supported MOFs, namely, [CuI4(2Et,3Me-Pyr)5(SiW12O40)] (1), [CuI4(2,6-Pyr)4(SiW12O40)] (2), [CuI4(2,5-Pyr)4(SiW12O40)(H 2 O)2 ] (3), [CuI 4 (2,3,5,6-Pyr)4 (SiW12 O40 )](H2 O) (4), Received: December 28, 2010 Revised: March 20, 2011 Published: March 30, 2011 1786

dx.doi.org/10.1021/cg1017246 | Cryst. Growth Des. 2011, 11, 1786–1797

Crystal Growth & Design Scheme 1. Structures of the Pyrazine Derivatives Used in This Work

[CuI4(2,5-Pyr)4(PMoVI11MoVO40)] 3 1.5H2O (5), [CuI3(2,3,5Pyr)4 (PMo 12 O40 )] 3 H2 O (6), and [Cu I4 (2Et,3Me-Pyr)5 (PMoVI11MoVO40)] (7) (2Et,3Me-Pyr = 2-ethyl-3-methylpyrazine; 2,6-Pyr = 2,6-dimethylpyrazine; 2,5-Pyr = 2,5-dimethylpyrazine; 2,3,5-Pyr = 2,3,5-trimethylpyrazine; and 2,3,5,6-Pyr = 2,3,5,6tetramethylpyrazine), have been synthesized under solvothermal conditions. Their structures have been determined by singlecrystal X-ray diffraction and further characterized by elemental analyses, thermogravimetric analysis (TGA), and IR spectra. The effects of the pyrazine derivatives and the Keggin polyanions on the structures of POM-supported MOFs have been discussed. In addition, the electrochemical properties of the compounds 1 and 6 have also been investigated in 1 M H2SO4 aqueous solution.

’ EXPERIMENTAL SECTION General Procedures. Chemicals were purchased from commercial sources and used without further purification. Physical Measurements. Elemental analyses were carried out with a Carlo Erba 1106 elemental analyzer, and the FT-IR spectra were recorded from KBr pellets in the range 4000400 cm1 on a Mattson Alpha-Centauri spectrometer. Inductively coupled plasma (ICP) analysis was carried out on a Perkin-Elmer Optima 3300 DV spectrometer. TGA was performed on a Perkin-Elmer TG-7 analyzer heated from 40 to 800 °C under nitrogen gas. X-ray powder diffraction (XRPD) was performed on a Siemens D5005 diffractometer. X-ray photoelectron spectroscopy (XPS) was measured on an Escalabmkii spectrometer with an Al KR (1486.6 eV) achromatic X-ray source. Electrochemical measurements were performed with a CHI660b electrochemical workstation. A conventional three-electrode system was used. A Ag/AgCl (3 M KCl) electrode was used as a reference electrode, and a Pt wire was used as a counter electrode. Chemically bulk-modified carbon-paste electrodes (CPEs) were used as the working electrodes. Synthesis of [CuI4(2Et,3Me-Pyr)5(SiW12O40)] (1). H4SiW12O40 (0.36 g, 0.125 mmol) and Cu(NO3)2 3 3H2O (0.12 g, 0.5 mmol) were dissolved in 8 mL of distilled water with stirring at room temperature. The pH value of the mixture was adjusted to 5 with 1.0 mol L1 NaOH, then a methanol solution (4 mL) of 2Et,3Me-Pyr (0.061 g, 0.5 mmol) was added, and the cloudy solution was put into a 18 mL Teflon-lined Parr and heated to 170 °C for 72 h. After the solution was slowly cooled to room temperature at a rate of 10 °C h1, red block crystals of 1 were

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filtered and washed with methanol and distilled water [42% yield based on Cu(NO3)2 3 3H2O]. Elem. and ICP anal. calcd (%) for C35H48Cu4N10O40SiW12 (Mr = 3737.28): C, 11.25; H, 1.29; N, 3.75; Si, 0.75; W, 59.03; Cu, 6.80. Found: C, 11.19; H, 1.37; N, 3.84; Si, 0.66; W, 59.15; Cu, 6.72. IR (cm1): 3860 (ws), 3744 (ws), 3440 (ws), 1645 (ws), 1515 (ws), 1425 (ms), 1173 (ws), 1013 (ms), 971 (ms), 919 (s), 792 (s), 527 (s). Synthesis of [CuI4(2,6-Pyr)4(SiW12O40)] (2). A mixture of H4SiW12O40 (0.36 g, 0.125 mmol), Cu2(OH)2CO3 (0.11 g, 0.5 mmol), 2,6-Pyr (0.054 g, 0.5 mmol), distilled water (8 mL), and methanol (4 mL) was stirred for 1 h at room temperature and then transferred and sealed in a 18 mL Teflon-lined stainless steel container. The container was heated to 170 °C for 72 h and then gradually cooled to room temperature at a rate of 10 °C h1. Red crystals of 2 were collected in 55% yield based on Cu2(OH)2CO3. Elem. and ICP anal. calcd (%) for C24H32Cu4N8O40SiW12 (Mr = 3561.03): C, 8.09; H, 0.91; N, 3.15; Si, 0.79; W, 61.95; Cu, 7.14. Found: C, 8.15; H, 0.98; N, 3.09. Si, 0.86; W, 61.84; Cu, 7.05. IR (cm1): 3421 (ms), 1623 (ms), 1515 (ms), 1429 (s), 1377 (ms), 1266 (ms), 1222 (ws), 1167 (ms), 1015 (s), 971 (s), 919 (s), 791 (s), 521 (s). Synthesis of [CuI4(2,5-Pyr)4(SiW12O40)(H2O)2] (3). A mixture of H4SiW12O40 (0.36 g, 0.125 mmol), Cu2(OH)2CO3 (0.11 g, 0.5 mmol), 2,5-Pyr (0.054 g, 0.5 mmol), distilled water (8 mL), and methanol (4 mL) was stirred for 1 h at room temperature and then transferred and sealed in a 18 mL Teflon-lined stainless steel container. The container was heated to 170 °C for 72 h and then gradually cooled to room temperature at a rate of 10 °C h1. Red crystals of 3 were collected in 47% yield based on Cu2(OH)2CO3. Elem. and ICP anal. calcd (%) for C24H32Cu4N8O42SiW12 (Mr = 3593.03): C, 8.02; H, 0.90; N, 3.12; Si, 0.78; W, 61.40; Cu, 7.07. Found: C, 7.96; H, 0.98; N, 3.05; Si, 0.88; W, 61.29; Cu, 7.15. IR (cm1): 3744 (ws), 3440 (ms), 1626 (ws), 1497 (ms), 1429 (ms), 1379 (ws), 1339 (ws), 1161 (ms), 1014 (s), 970 (s), 919 (s), 792 (s), 523 (s). Synthesis of [CuI4(2,3,5,6-Pyr)4(SiW12O40)](H2O) (4). A mixture of H4SiW12O40 (0.36 g, 0.125 mmol), Cu2(OH)2CO3 (0.11 g, 0.5 mmol), 2,3,5,6-Pyr (0.068 g, 0.5 mmol), distilled water (8 mL), and methanol (4 mL) was stirred for 1 h at room temperature and then transferred and sealed in a 18 mL Teflon-lined stainless steel container. The container was heated to 170 °C for 72 h and then gradually cooled to room temperature at a rate of 10 °C h1. Red crystals of 4 were collected in 68% yield based on Cu2(OH)2CO3. Elem. and ICP anal. calcd (%) for C32H50Cu4N8O41SiW12 (Mr = 3691.25): C, 10.41; H, 1.37; N, 3.04; Si, 0.76; W, 59.77; Cu, 6.88. Found: C, 10.36; H, 1.30; N, 2.96; Si, 0.64; W, 59.86; Cu, 6.76. IR (cm1): 3860 (ws), 3744 (ws), 3419 (ms), 1644 (ws), 1515 (ws), 1428 (ms), 1177 (ws), 1013 (ws), 968 (ms), 920 (s), 796 (s), 518 (s).

Synthesis of [CuI4(2,5-Pyr)4(PMoVI11MoVO40)] 3 1.5H2O (5).

H3[PMo12O40] 3 13H2O (0.30 g, 0.15 mmol) and Cu(CH3COO)2 3 2H2O (0.11 g, 0.5 mmol) were dissolved in 8 mL of distilled water with stirring at room temperature. The pH value of the mixture was adjusted to 4 with 1.0 mol L1 NaOH, then an ethanol solution (4 mL) of 2,5-Pyr (0.054 g, 0.5 mmol) was added, and the cloudy solution was put into a 18 mL Teflonlined Parr and heated to 170 °C for 72 h. After the solution was slowly cooled to room temperature at a rate of 10 °C h1, black block crystals of 5 were obtained in 65% yield based on Cu(CH3COO)2 3 2H2O. Elem. and ICP anal. calcd (%) for C24H35Cu4Mo12N8O41.50P (Mr = 2536.01): C, 11.37; H, 1.39; N, 4.42; P, 1.22; Mo, 45.40; Cu, 10.02. Found: C, 11.29; H, 1.33; N, 4.31. P, 1.31; Mo, 45.52; Cu, 10.10. IR (cm1): 3860 (ws), 3743 (w), 3678 (ws), 3443 (ws), 3046 (ws), 1740 (ws), 1693 (ws), 1644 (ws), 1497 (ms), 1428 (ms), 1378 (ws), 1338 (ws), 1158(ws), 1056 (ms), 953 (s), 867 (ws), 783 (s), 500 (s). Synthesis of [CuI3(2,3,5-Pyr)4(PMo12O40)] 3 H2O (6). H3[PMo12O40] 3 13H2O (0.30 g, 0.15 mmol) and Cu(CH3COO)2 3 2H2O (0.11 g, 0.5 mmol) were dissolved in 8 mL of distilled water with stirring at room temperature. The pH value of the mixture was adjusted to 4 with 1.0 mol L1 NaOH, then a ethanol solution (4 mL) of 2,3,5-Pyr 1787

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0.0405 0.0586 0.1745

C24H32Cu4N8O42SiW12 3593.03 0.24 0.18 0.16 monoclinic C2/c 24.800(5) 11.392(5) 25.025(5) 90 116.474(5) 90 6329(3) 4 0.892 22039/7924 0.0472 0.0389 0.0872 C24H32Cu4N8O40SiW12 3561.03 0.12 0.10 0.06 orthorhombic Pbca 22.254(5) 11.464(5) 23.344(5) 90 90 90 5956(3) 4 0.997 37212/7839 0.1361 0.0694 0.1838 empirical formula fw crystal size (mm3) crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) volume (Å3) Z GOF reflns collected/unique Rint R1 [I > 2σ(I)] wR2 (all data)

C35H48Cu4N10O40SiW12 3737.28 0.16 0.12 0.10 monoclinic P21/n 12.9036(5) 11.9095(3) 22.3016(10) 90 91.791(4) 90 3425.5(2) 2 0.874 27325/6247 0.1012 0.0582, 0.1477

3

C32H50Cu4N8O41SiW12 3691.25 0.22 0.20 0.16 monoclinic C2/c 12.6564(5) 22.9398(10) 24.7425(9) 90 99.040(3) 90 7094.4(5) 4 0.735 13754/6486 0.0522 0.0382 0.0703

C24H35Cu4Mo12N8O41.50P 2536.01 0.32 0.12 0.12 monoclinic C2/c 23.4725(7) 12.0745(3) 23.1288(7) 90 112.811(4) 90 6042.4(3) 4 0.859 27269/5759 0.0445 0.0416 0.0964

C28H40Cu3Mo12N8O41P 2517.55 0.20 0.14 0.12 orthorhombic Pnma 17.592(5) 22.091(5) 15.733(5) 90 90 90 6114(3) 4 1.155 15416/6996 0.0591 0.0835 0.1777

C35H38Cu4Mo12N10O40P 2675.16 0.25 0.20 0.11 monoclinic P21/n 12.8567(4) 11.8861(3) 22.4652(7) 90 92.158(3) 90 3430.61(17) 2 0.844

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2 1

Table 1. Crystal Data and Structure Refinements for Compound 17

4

5

6

7

Crystal Growth & Design

(0.061 g, 0.5 mmol) was added, and the cloudy solution was put into a 18 mL Teflon-lined Parr and heated to 170 °C for 72 h. After the solution was slowly cooled to room temperature at a rate of 10 °C h1, black crystals of 6 were obtained in 71% yield based on Cu(CH3COO)2 3 2H2O. Elem. and ICP anal. calcd (%) for C28H40Cu3Mo12N8O41P (Mr = 2517.55): C, 13.36; H, 1.60; N, 4.45; P, 1.23; Mo, 45.73; Cu, 7.57. Found: C, 13.24; H, 1.55; N, 1.69; P, 1.12; Mo, 45.80; Cu, 7.45. IR (cm1): 3860 (ws), 3744 (ws), 3443 (ws), 1644 (ws), 1516 (ws), 1428 (ms), 1169 (ws), 1059 (ms), 953 (s), 865 (ws), 799 (s), 495 (s). Synthesis of [CuI4(2Et,3Me-Pyr)5(PMoVI11MoVO40)] (7). H3[PMo12O40] 3 13H2O (0.30 g, 0.15 mmol) and Cu(CH3COO)2 3 2H2O (0.11 g, 0.5 mmol) were dissolved in 8 mL of distilled water with stirring at room temperature. The pH value of the mixture was adjusted to 4 with 1.0 mol L1 NaOH, then a ethanol solution (4 mL) of 2Et,3Me-Pyr (0.061 g, 0.5 mmol) was added, and the cloudy solution was put into a 18 mL Teflon-lined Parr and heated to 170 °C for 72 h. After the solution was slowly cooled to room temperature at a rate of 10 °C h1, black block crystals of 7 were obtained in 61% yield based on Cu(CH3COO)2 3 2H2O. Elem. and ICP anal. calcd (%) for C35H38Cu4Mo12N10O40P (Mr = 2675.16): C, 15.71; H, 1.43; N, 5.24; P, 1.16; Mo, 43.04; Cu, 9.50. Found: C, 15.64; H, 1.52; N, 5.34; P, 1.20; Mo, 43.11; Cu, 9.41. IR (cm1): 3860 (ws), 3743 (ws), 3648 (ws), 3423 (ms), 1740 (ws), 1693 (ws), 1644 (ws), 1515 (ms), 1454 (ws), 1423 (ws), 1166 (ws), 1052 (ws), 952 (s), 865 (ws), 784 (s), 493 (s). X-ray Crystallography. Single-crystal X-ray diffraction data for compounds 17 were recorded on an Oxford Diffraction Gemini R CCD with graphite-monochromated Mo KR radiation (λ = 0.71073 Å) at 293 K. The structures were solved with the direct method of SHELXS979 and refined with full-matrix least-squares techniques using the SHELXL-97 program10 within WINGX.11 Some disordered O atoms of complexes were refined with isotropic temperature parameters, and other nonhydrogen atoms were refined anisotropically. The hydrogen atoms attached to carbons were generated geometrically. In the complexes 1, 2, and 7, the disordered O and C atoms were refined using O and C atoms split over two sites, with a total occupancy of 1. The hydrogen atoms of the disordered C atoms were not included in the model. The hydrogen atoms attached to coordinated water in compound 3 were not located from difference Fourier maps. In compound 4, the occupancy of O1W atom was assigned 0.5 without H atoms. In compound 5, the occupancies of two water O atoms, O1W and O2W, were assigned 0.5 and 0.25 with no H atoms, respectively. Hydrogen atoms of other water molecules of the complexes were located from difference Fourier maps and refined with isotropic displacement parameters. The detailed crystallographic data and structure refinement parameters for 17 are summarized in Table 1.

’ RESULTS AND DISCUSSION Selected bond distances and angles for compounds 17 are listed in Table S1 (see the Supporting Information). The networks of compounds 17 were analyzed by using the OLEX program.12 Syntheses of the Compounds 17. Hydrothermal synthesis has recently been proven to be a particularly useful technique in the preparation of organicinorganic hybrid materials.13 Many POM-supported MOFs with diverse structural architectures have been synthesized by using hydrothermal methods. On the basis of the hydrothermal methods, we tried to synthesize compounds 17. Unfortunately, we only obtained a small quantity of microcrystals unsuitable for single-crystal X-ray diffraction. Thus, we sensed that solvothermal method may be helpful for crystal growth. In view of this, methanolwater or ethanolwater systems are applied in these experiments. As 1788



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Figure 1. (a) Stick/polyhedral view of the coordination environments of SiW12O404 and CuI anions in 1. (b) View of the 2D sheet structure of 1. (c) Perspective view of 2D layer containing the (SiW12O40)4 anions. (d) Perspective view of 3D framework in 1. (e) Schematic view of the 3D openframework in 1. (f) Schematic view of the (3,4)-connected framework with (63)(416481)(4262102) topology in 1.

expected, the crystals of the compounds 17 were isolated with high yields under solvothermal conditions. In the process of solvothermal synthesis, several factors can influence the formation of crystal phases, such as initial reactants, molar ratio, organic solvent, pH value, reaction time, and temperature, etc. In this work, parallel experiments showed that the organic ingredient of the solvent is crucial for the crystallization of compounds 17. The crystals of compounds 14 containing the (SiW12O40)4 polyanions could only be obtained at the H2O/CH3OH solvothermal conditions. However, the crystals of compounds 57 containing the (PMo12O40)3 anions could be obtained at the H2O/C2H5OH solvothermal conditions. In addition, the nature of the CuII salt is crucial for the formation of the compounds. We tried to replace Cu(NO3)2 3 3H2O with CuCl2 3 2H2O, Cu2(OH)2CO3, or Cu(CH3COO)2 3 2H2O in the synthesis of compound 1, but no suitable crystals for single-crystal X-ray diffraction were obtained. For compounds 24, when the Cu2(OH)2CO3 salt was introduced at the

solvothermal conditions, their crystals could be obtained with high yields. However, when Cu2(OH)2CO3 was replaced with Cu(CH3COO)2 3 2H2O, the crystals of compounds 57 were obtained with high yields. From the syntheses of these compounds, it can be seen that the organic ingredient of the solvent and the nature of the metal salt play important roles in the crystallization of 17. Structure of [CuI4(2Et,3Me-Pyr)5(SiW12O40)] (1). Singlecrystal X-ray study reveals that the structure of 1 is a 3D framework constructed by 2D copper(I)organic sheets and (SiW12O40)4 building blocks. The (SiW12O40)4 polyanion exhibits a distorted R-Keggin structure. The central Si1 atom is surrounded by a distorted cube constituted of eight oxygen atoms with each oxygen site half-occupied. This structure feature often appears in the Keggin structure.14 Complex 1 consists of two CuI ions, two and a half 2Et,3Me-Pyr ligands, and half a (SiW12O40)4 anion lying on an independent inversion center. As shown in Figure 1a, Cu1 cation is four-coordinated by two 1789



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Figure 2. (a) Stick/polyhedral view of the coordination environments of SiW12O404 and CuI anions in 2. (b) View of 2D double layer in 2. Right: 2D layer along the b-axis. (c) Perspective view of 3D framework in 2. (d) Schematic view of the (3,4,6)-connected framework with (51 3 72) (51 3 61 3 74)(51 3 62 3 75 3 85 3 91 3 101) topology in 2.

nitrogen atoms [Cu(1)N(1) = 1.896(19) and Cu(1)N(5) = 1.886(19) Å] from two 2Et,3Me-Pyr molecules and two terminal oxygen atoms [Cu(1)O(13)#3 = 2.594(19) and Cu(1)O(18) = 2.606(19) Å] from two (SiW12O40)4 anions, showing a distorted tetrahedral coordination geometry. The CuO bond distances are within the normal range observed in other CuIcontaining POM-supported MOFs.6f,15 Cu2 is three-coordinated by three nitrogen atoms [Cu(2)N(2) = 1.992(16), Cu(2)N(4) = 1.977(19), and Cu(2)N(3)#1 = 1.987(16) Å] from three 2Et,3Me-Pyr ligands. The 2Et,3Me-Pyr ligands link CuI cations to generate a unique 2D (10,3) sheet, showing a hexagonal window with the dimensions of 19.691 6.659 6.659 Å3 (Figure 1b). In the (10,3) sheet, 10 CuI catiions are linked by 10 2Et,3Me-Pyr ligands to form a large hexagonal 50-membered ring. To the best of our knowledge, the 50-membered copper-Pyr ring in 1 is the largest

example reported in the copper complexes containing pyrazine derivatives to date.6d,16 In compound 1, the (10,3) sheets repeat in an ABAB stacking sequence instead of the AA stacking fashion (Figure S1, see the Supporting Information). As shown in Figure 1c, the (SiW12O40)4 anions, which are located on the half of the hexagonal voids of the sheet, link two Cu1 anions of the hexagonal void through its two terminal oxygen atoms. However, the other two terminal oxygen atoms of the (SiW12O40)4 anion further connect the two Cu1 anions from the adjacent layers, leading to a 3D framework structure (Figure 1d). The (SiW12O40)4 anions locate on the voids of the highly open 3D framework (Figure 1e). Such a linking mode results in the (SiW12O40)4 anion being a four-connected linkage surrounded by four Cu-2Et,3Me-Pyr chains (Figure 1a). From the topological view, if (SiW12O40)4 and Cu1 anions are considered as four-connected nodes, and Cu2 cations are regarded as 1790



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Figure 3. (a) Stick/polyhedral view of the coordination environments of SiW12O404 and CuI anions in 3. (b) View of 2D double layer in 3. Right: 2D layer along the b-axis. (c) Schematic view of (42 3 64)(41 3 64 3 81) topology in 3.

three-connected nodes, the structure of 1 is a novel (3,4)connected framework with (63)(41 3 64 3 81)(42 3 62 3 102) topology. Structure of [CuI4(2,6-Pyr)4(SiW12O40)] (2). Complex 2 consists of two CuI ions, two 2,6-Pyr ligands, and half a (SiW12O40)4 anion lying on an independent inversion center. Crystal structure analysis reveals that there are two independent CuI centers, in which Cu2 is three-coordinated by two nitrogen atoms of the 2,6Pyr ligands and one oxygen atom of one (SiW12O40)4 anion in a distorted trigonal coordination geometry, and Cu1 is fourcoordinated by two nitrogen atoms of the 2,6-Pyr ligands and two oxygen atoms of two (SiW12O40)4 anions in a tetrahedral coordination geometry as shown in Figure 2a. The CuN bond distances range from 1.919(19) to 1.963(14) Å, and the CuO bond lengths range from 2.130(15) to 2.614(16) Å. In 2, the CuI cations are first bridged by 2,6-Pyr ligands to form a 1D “zigzag” chain (Figure S2, see the Supporting Information). These adjacent chains are further linked by four terminal oxygen atoms from the (SiW12O40)4 anion to form a 2D double layer (Figure 2b). Furthermore, the Cu1 cations of these layers are connected by the terminal oxygen atoms of (SiW12O40)4 anions from the adjacent layers to form a 3D framework (Figure 2c). Unlike compound 1, each (SiW12O40)4 anion as a six-connected linkage coordinated to six CuI cations from six adjacent 1D CuPyr chains (Figure 2a). To the best of our knowledge, the hexadentate coordination modes of (SiW12O40)4 anion are rarely observed in the POM-based MOFs.6e From the topological view, if (SiW12O40)4 anion is considered as a six-connected node, and Cu1 and Cu2 anions are regarded as four- and

three-connected nodes, respectively; the structure of 2 can be described as a rare trinodal (3,4,6)-connected (51 3 72)(51 3 61 3 74)(51 3 62 3 75 3 85 3 91 3 101) topology (Figure 2d). Structure of [CuI4(2,5-Pyr)4(SiW12O40)(H2O)2] (3). Complex 3 consists of two CuI cations, two 2,5-Pyr ligands, and half a (SiW12O40)4 anion lying on an independent inversion center. As shown in Figure 3a, the Cu1 cation is three-coordinated by two nitrogen atoms [Cu(1)N(1) = 1.918(8) and Cu(1) N(3) = 1.923(8) Å] from two different 2,5-Pyr ligands and one oxygen atom [Cu(1)O(1W) = 2.337(17) Å] from one water molecule. Cu2 cation is four-coordinated by two nitrogen atoms [Cu(2)N(4)#1 = 1.925(7) and Cu(2)N(2) = 1.931(7) Å] from two 2,5-Pyr molecules and two oxygen atoms [Cu(2) O(11) = 2.719(7) and Cu(2)O(13)#4 = 2.466(7) Å] from the different (SiW12O40)4 anions, showing a distorted tetrahedral coordination geometry. In 3, the CuI centers are bridged by 2,5Pyr ligands to form a 1D chain structure (Figure S3, see the Supporting Information). Each SiW12O404 anion, as a fourconnected linkage and links four adjacent CuPyr chains to generate a 2D double layer parallel to the ab plane (Figure 3b). From the topological view, if (SiW12O40)4 anion and Cu2 cation are considered as four-connected nodes, and the 2.5-Pyr ligand is regarded as a linkage, the structure of 3 is a 4-connected network with (42 3 64)(41 3 64 3 81) topology (Figure 3c). Structure of [CuI4(2,3,5,6-Pyr)4(SiW12O40)](H2O) (4). Compound 4 consists of two CuI cations, two 2,3,5,6-Pyr ligands, half a SiW12O404 anion lying on an independent inversion center, and half a lattice water molecule. As shown in Figure 4a, the Cu1 1791



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Figure 4. (a) Stick/polyhedral view of the coordination environments of SiW12O404 and CuI anions in 4. (b) Interlaced arrangement of the Cu2,3,5,6-Pyr chains in 4. (c) View of 2D double layer in 4. Right: 2D layer along the b-axis.

cation is four-coordinated by two N atoms from two 2,3,5,6-Pyr ligands and two O atoms from two SiW12O404 anions in a distorted tetrahedral geometry. The bond distances around the Cu1 ion are 1.897(12) and 1.919(12) Å for CuN and 2.720(12) and 2.777(12) Å for CuO. The Cu2 cation adopts a linear geometry, coordinated by two N atoms from two 2,3,5,6Pyr ligands with CuN bond distances of 1.869(13) and 1.887(12) Å. In compound 4, the CuI cations are first bridged by 2,3,5,6-Pyr molecules to form a 1D chain structure. Unlike compound 3, the 1D chains interlace with each other in 4 (Figure 4b). The SiW12O404 anion shows the tetradentate coordination mode. In this mode, the SiW12O404 anions connect the Cu1 cations of the staggered chains to give a 2D double layer (Figure 4c). It was noted that, even though coordination environments of the cations and packing mode in 4 are different from those in 3, the topology of 4 is very similar to that of 3. The structure of 4 is also a 4-connected network with (42 3 64)(41 3 64 3 81) topology (Figure S4, see the Supporting Information). Structure of [CuI4(2,5-Pyr)4(PMoVI11MoVO40)] 3 1.5H2O (5). Single-crystal X-ray diffraction analysis shows that the asymmetric unit of 5 consists of two CuI cations, two 2,5-Pyr ligands, half a one-electron-reduced (PMo12O40)4 anion lying on an independent inversion center, and three-quarters of a lattice water molecule. The polyanion in 5 exhibits a distorted R-Keggin structure with P atom at the center surrounded by a cube of eight half-occupied oxygen atoms, surrounded by four vertex-sharing Mo3O13 trimers that result from the association of three edgesharing MoO6 octahedra. This structural feature often appears in [XMo12O40]n with the R-Keggin structure.14 In compound 5, one of Mo atoms is in the þV oxidation state, and all of the Cu atoms are in the þI oxidation states, based on the charge balance consideration, XPS spectra, and bond valence sum calculations.17

As shown in Figure 5a, Cu1 cation is four-coordinated by two nitrogen atoms [Cu(1)N(4)1 = 1.914(6) and Cu(1)N(1) = 1.922(6) Å] from two 2,5-Pyr molecules and two oxygen atoms [Cu(1)O(20) = 2.418(7) and Cu(1)O(19) = 2.645(6) Å] from the same (PMo12O40)4 anion, showing a distorted tetrahedral coordination geometry. Cu2 is three-coordinated by two nitrogen atoms [Cu(2)N(2) = 1.916(6) and Cu(2)N(3) = 1.921(6) Å] from two 2,5-Pyr ligands and one oxygen atom [Cu(2)O(15)4 = 2.563(6) Å] from other (PMo12O40)4 anion, showing a T-shaped coordination geometry. In 5, the CuI cations are also bridged by 2,5-Pyr molecules to form a 1D chain structure (Figure S5, see the Supporting Information). Unlike compound 3, each (PMo12O40)4 anion with the bidentate chelating mode coordinates to two Cu1 cations, and the Cu1 cations of adjacent chains are bridged by the (PMo12O40)4 anions to form a 2D double sheet (Figure 5b). The Cu2 cations of these layers are further linked by the terminal oxygen atoms of the (PMo12O40)4 anions from the adjacent layers to form a 3D framework (Figure 5c). Notably, the (PMo12O40)4 anion, as both the tetradentate bridging ligand and the chelating ligand, coordinates to four CuI cations from four adjacent 1D CuPyr chains of 5 (Figure 5a). From the topological view, if each (PMo12O40)4 is considered as a four-connected node, Cu1 and Cu2 cations are regarded as three-connected nodes, and the 2,5Pyr liagnd is considered as a linkage, the structure of 5 can be described as a (3,4)-connected framework with (61 3 81 3 121)2(62 3 81 3 123) topology (Figure 5d). Structure of [CuI3(2,3,5-Pyr)4(PMo12O40)] 3 H2O (6). As shown in Figure 6a, the structure of 6 contains two CuI cations, one of which, Cu1, lies on an inversion center; three 2,3,5-Pyr ligands, two of them lie on another inversion center; half a (PMo12O40)3 anion lying about an inversion center; and half a 1792



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Figure 5. (a) Stick/polyhedral view of the coordination environments of (PMo12O40)4 and CuI anions in 5. (b) View of 2D double layer in 5. Right: 2D layer along the b-axis. (c) Perspective view of 3D framework in 5. (d) Schematic view of (61 3 81 3 121)2(62 3 81 3 123) topology in 5.

lattice water molecule. Similar to that in 5, the (PMo12O40)3 cluster also shows a disordered “R-Keggin” structure. The central P atom is surrounded by a cube of eight half-occupied oxygen atoms.14 The Cu1 cation exhibits a linear coordination environment, completed by two nitrogen atoms [CuN = 1.98(2) Å] from two different 2,3,5-Pyr ligands. The Cu2 cation is threecoordinated by three nitrogen atoms [Cu(2)N(1) = 2.00(2), Cu(2)N(2) = 2.001(17), and Cu(2)N(3) = 2.042(19) Å] from three distinct 2,3,5-Pyr ligands, showing a trigonal coordination geometry. All copper sites exhibit þ1 oxidation state, confirmed by bond valence sum calculations17 and the particular coordination environments of CuI. In 6, the CuI centers are linked by the 2,3,5-Pyr ligands to form a novel 2D (8,3) sheet, showing a hexagonal window with the dimensions of 17.592 6.737 6.714 Å3, which contains eight CuI cations and eight 2,3,5-Pyr liagnds (Figure 6b). To the best of our knowledge, the (8,3)

network of CuPyr compounds has not been reported.6d,16 As shown in Figure 6c, the (PMo12O40)3 cluster is linearly arranged on the hexagonal voids in the (8,3) network. If the weak Cu 3 3 3 O interactions with two terminal oxygen atoms [Cu(1)O(12) = 2.860(2) and Cu(1)O(15) = 2.835(2) Å] from the same (PMo12O40)3 anion is considered, each (PMo12O40)3 anion in a bidentate chelating coordination mode links two Cu1 cations to give a 1D inorganic chain (Figure S6 in the Supporting Information). Like compound 1, the sheets of 6 also repeat in an ABAB stacking sequence (Figure 6d). Structure of [CuI4(2Et,3Me-Pyr)5(PMoVI11MoVO40)] (7). Crystal structural analysis reveals that complex 7 is an isomorphous structure with complex 1. The only difference between 7 and 1 is the heteropolyanions. As shown in Figure 7, the structure of 7 is composed of two CuI cations, two and a half 2Et,3Me-Pyr ligands, and half a one-electron-reduced (PMo12O40)4 anion 1793



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Figure 6. (a) Stick/polyhedral view of the coordination environments of (PMo12O40)3 and CuI anions in 6. (b) View of the 2D sheet structure of 6. (c) Perspective view of 2D layer containing the (PMo12O40)3 anions. (d) Schematic representation of the ABAB stacking sequence of 2D sheets in 6.

Effects of the Pyrazine Derivatives on the Structures of the Complexes. In this work, to investigate the influence of the

Figure 7. Stick/polyhedral view of the coordination environments of PMo12O404 and CuI anions in 7.

lying on an independent inversion center. Similar to that in 5, the (PMo12O40)4 cluster also shows a typical disordered “RKeggin” structure. The central P atom is surrounded by a cube of eight half-occupied oxygen atoms.14 The valence sum calculations,17 XPS spectra, and the charge balance consideration show that one Mo atom is in the þV oxidation state, and all of the Cu atoms are in the þI oxidation states. In 7, the (PMo12O40)4 anion, as a tetrademtate ligand, connects with the adjacent CuPyr layers to generate a similar 3D structure to 1. The bond distances of CuN and CuO in 7 are comparable to those in 1. The diagrams of the structure of 7 are shown in Figure S3 (see the Supporting Information).

pyrazine derivatives on the complex structures, typical pyrazine derivatives such as 2Et,3Me-Pyr, 2,6-Pyr, 2,5-Pyr, 2,3,5-Pyr, and 2,3,5,6-Pyr were used under similar synthetic conditions. Although 14 contain the same CuI cations and (SiW12O40)4 anions, they display distinct structural topologies. The structural differences of 14 are mainly caused by the steric effects of the pyrazine derivatives (Scheme 1). In 1, the 2Et,3Me-Pyr ligands and the tetradentate (SiW12O40)4 anions link the CuI cations to generate a 3D (3,4)-connected framework. When 2Et,3Me-Pyr is replaced by 2,6-Pyr, compound 2, showing a 3D (3,4,6)-connected framework, was obtained under the similar synthetic condition. In contrast with 2,5-Pyr of compound 3, there are two additional methyl groups in 2,3,5,6-Pyr of compound 4. Although they show similar 2D double layer structures, their CuIorganic chains possess different extended modes. Unlike compound 3, the 1D chains interlace each other in 4. Obviously, the structural differences among 14 mainly can be attributed to the substituent positions and numbers of pyrazine derivatives. It should be pointed out that the structures of compounds 14 are entirely different from the ones of two reported compounds {[Cu(pz)1.5]4(SiW12O40)(H2O)3}n (8) (pz = pyrazine) and {[Cu(2,3-Me2pz)1.5]4(SiW12O40)}n (9) (2,3-Me2pz = 2,3dimethylpyrazine).6d In 8 and 9, the pyrazine derivatives link CuI cations to form similar 2D (41 3 82) sheets. However, the (SiW12O40)4 anions do not coordinate to the CuI cations. The structural differences caused by steric effects of the pyrazine derivatives can also be supported by compounds 57. 1794



Figure 8. Coordination modes of Keggin polyanions.

In 5, the 2,5-Pyr ligands and the (PMo12O40)4 anions link the CuI cations to generate a 3D(3,4)-connected framework. As compared with 2,5-Pyr, 2,3,5-Pyr has an additional methyl group at 3-position. When the 2,3,5-Pyr was used under the similar reaction condition of 5, a 2D 3-connected (8,3) sheet of 6 was obtained. The (PMo12O40)4 is located in the window of the sheet through the weak CuO bonds. Notably, the structures of compounds 5 and 6 are also completely different from the reported related compound {[Cu(2-Mepz)1.5]3(PMo12O40)(H2O)3.5}n (10) (2-Mepz = 2-methylpyrazine).6d In the reported 10, the 2-Mepz bridges the CuI cations to form a 2D (63) sheet, in which the guest (PMo12O40)3 anions are included. Coordination Modes of Keggin Type Polyanions. The Keggin type polyanions can coordinate to metal ions in a variety of coordination modes to form compounds with different dimensions.15b,18 As shown in Figure 8, the Keggin type polyanions in 17 adopt four different coordination modes, which have significant effects on the final structures of the compounds. In compounds 1 and 7, each polyanion acts as a tetradentate ligand (Figure 8a) and coordinates to four CuI cations from different CuPyr sheets to generate 3D structures. In 3 and 4, although polyanions also act as tetradentate ligands (Figure 8a), they link four adjacent CuPyr chains to form 2D double sheets. The structural changes may be explained by the structural effect of different copper(I)organic frameworks. In 2, copper(I)organic framework only exhibits a 1D chain structure. However, compound 2 shows a 3D framework due to the six-connected polyanion linkage (Figure 8b). In compound 5, the polyanion, as both the tetradentate bridging ligand and the chelating ligand (Figure 8c), links the adjacent CuPyr chains to give a 3D structure. In 6, the Keggin polyanion in the bisbidentate chelating coordination mode bridges two CuI cations of the same copper(I)organic sheet (Figure 8d). On the basis of above description, it can be seen that the coordination behaviors of Keggin polyanions, such as the coordination number and the coordination geometry, have great influence on the frameworks of the complexes. These coordination modes further enrich the coordination chemistry of the Keggin polyanions. IR, XPS, and XRPD Analyses. In the IR spectra (see Figure S8 in the Supporting Information), characteristic peaks at 1015, 971, 919, 791, and 521 cm1 for 1, 1015, 971, 919, 791, and

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521 cm1 for 2, 1014, 970, 919, 792, and 523 cm1 for 3, and 1013, 968, 920, 796, and 518 cm1 for 4 are attributed to v(SiOa), v(WOd), v(WObW), and v(WOcW) of the (SiW12O40)4 polyanion, respectively. The characteristic peaks at 1056, 953, 863, and 783 cm1 for 5, 1059, 953, 865, and 799 cm1 for 6, and 1052, 952, 865, and 784 cm1 for 7 are attributed to v(POa), v(MoOd), v(MoObMo), and v(MoOcMo) of the (PMo12O40)3 polyanion, respectively.19 Furthermore, a series of characteristic bands in the 11501740 and 34403860 cm1 are attributed to the pyrazine derivatives. The oxidation states of Mo and Cu in 57 are further confirmed by XPS measurements. In the XPS spectra (Figure S9 in the Supporting Information), two overlapped peaks at 232.8 and 231.4 eV for 5 and 232.8 and 231.7 eV for 7 are attributed to Mo6þ (3d5/2) and Mo5þ (3d5/2), respectively. Two peaks at 232.6 and 235.9 eV for 6 are ascribed to Mo6þ (3d5/2) and Mo6þ (3d3/2), respectively.20 Two peaks at 932.6 and 952.7 eV for 5, 932.8 and 953.1 eV for 6, and 932.4 and 952.3 eV for 7 are attributed to Cuþ (2p3/2) and Cuþ (2p1/2), respectively.21 The XPS results further confirm the structure analysis. Figure S10 (see the Supporting Information) presents the XRPD patterns for compounds 17. The diffraction peaks of both simulated and experimental patterns match well in relevant positions, indicating thus the phase purities of the compounds 17. Thermal Analysis. To characterize the compounds more fully in terms of thermal stability, their thermal behaviors were studied by TGA. The experiments were performed under a N2 atmosphere with a heating rate of 10 °C/min in temperatures ranging from room temperature to 800 °C (Figure S11 in the Supporting Information). The anhydrous compound 1 begins to decompose at 285 °C and ends above 640 °C. The weight loss is attributed to the 2Et,3Me-Pyr ligands (obsd, 17.71%; calcd, 16.27%). The TGA curve of 2 shows that the weight loss from 245 to 630 °C corresponds to the removal of 2,6-Pyr ligand (obsd, 12.92%; calcd, 12.27%). For compound 3, there are two distinct weight loss procedures in the temperature range of 50120 °C, corresponding to the loss of two water molecules per formula unit (obsd, 1.15%; calcd, 1.00%). The second weight loss of 12.12% (calcd, 11.91%) in the temperature range of 360680 °C can be assigned to the release of 2,5-Pyr ligand. The TGA curve of compound 4 has two weight loss processes. The weight loss (0.63%) from room temperature to 95 °C is attributed to the removal of free water molecules (calcd, 0.49%). The remaining structure begins to decompose at 312 °C and ends above 638 °C. The hydrous compound 5 loses its water molecule (obsd, 0.95%; calcd, 1.06%) from room temperature to 121 °C. The removal of the anhydrous compound occurs in the temperature range of 334545 °C, corresponding to the loss of 2,5-Pyr ligand. For 6, the weight loss attributed to the gradual release of water molecules (obsd, 0.94%; calcd, 0.72%) is observed from 50 to 225 °C. The removal of organic components occurs from 345 to 555 °C. The anhydrous compound 7 begins to decompose at 304 °C and ends above 560 °C. The weight loss is attributed to the 2Et,3Me-Pyr liagnds (obsd, 22.01%; calcd, 22.35%). Voltammetric Behaviors of 1-CPE and 6-CPE in Aqueous Electrolyte. Compounds 17 are insoluble in water and common organic solvents. Thus, the bulk-modified CPE becomes the optimal choice to study the electrochemical properties of these compounds. The electrochemical behaviors of the compounds 14 are similar, and the electrochemical behaviors of the compounds 57 are also homologous. Thus, the 1-CPE and 1795



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Figure 9. (a) Cyclic voltammograms of the 1-CPE and (b) 6-CPE in 1 M H2SO4 at different scan rates (from inner to outer: 20, 50, 100, 150, 200, 250, 300, 350, 400, 450, and 500 mV s1).

6-CPE cases have been taken as examples to study their electrochemical properties. The 1- and 6-modified CPE (1-CPE and 6-CPE) were fabricated according to the literature.22 Figure 9 shows the cyclic voltammogram behaviors at a potential range from 600 to 800 mV for 1-CPE and from 160 to 800 mV for 6-CPE at different scan rates. The peak potentials change gradually following the scan rates from 20 to 500 mV s1. The cathodic peak potentials shift toward the negative direction, and the corresponding anodic peak potentials shift to the positive direction with increasing scan rates. The results verify that the redox ability of the polyanions can be maintained in the hybrid solids. As shown in Figure 9a, it can be seen that two irreversible redox peaks of 1 appear in 1 M H2SO4 aqueous solution, respectively. The mean peak potentials E1/2 = (Epa þ Epc)/2 are þ274 mV (I) and 147 mV (II) (50 mV s1), respectively. Redox peaks II0 and IIII0 correspond to two-electron processes of W.23 For 6-CPE, there are three pairs of reversible redox peaks in 1 M H2SO4 aqueous solution (Figure 9b). The mean peak potentials E1/2 = (Epa þ Epc)/2 are þ401 mV (I), þ205 mV (II), and 21 mV (III) (50 mV s1), respectively. Redox peaks II0 , IIII0 , and IIIIII0 correspond to three consecutive two-electron processes of Mo.5h,22 However, the oxidation peaks of the copper(I) centers are not observed in the potential ranges of 160 to 800 mV for 6 and 600 to 800 mV for 1. This phenomenon has been observed in the similar Cu/POM systems.5k,23a,24 The electrochemical results indicate that these hybrid compounds are potential electrocatalyst and modified electrode materials.23b,25

’ CONCLUSION In this paper, we have successfully synthesized seven POMsupported hybrid materials based on Keggin type polyanions and copper(I)organic frameworks under solvothermal conditions. These complexes show fascinating 2D and 3D frameworks with the various topologies. The structural diversities indicate that the substituting groups of the pyrazine derivatives, and the coordination modes of the Keggin polyanions play important roles in the formation of the POM-based MOFs. This work not only provides very useful information for the assembly of POM-based MOFs but also further enriches the crystal engineering of the Keggin polyanions. ’ ASSOCIATED CONTENT

bS

Supporting Information. X-ray crystallographic files (CIF); IR spectra, XRPD, XPS, and TGA of the compounds

17; selected bond lengths and angles; perspective view of 2D sheet in 1; schematic view of the chain of 2, 3, 5, and 6; schematic view of (42 3 64)(41 3 64 3 81) topology in 4; and diagrams of the structure of 7. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (J.Y.). Fax: þ86-43185098620. E-mail: [email protected] (J.-F.M.).

’ ACKNOWLEDGMENT We thank the Program for Changjiang Scholars and Innovative Research Teams in Chinese Universities, the National Natural Science Foundation of China (Grant Nos. 21071028 and 21001023), the Science Foundation of Jilin Province (20090137 and 20100109), the Science Foundation of Heilongjiang (B201017), the Fundamental Research Funds for the Central Universities, the Specialized Research Fund for the Doctoral Program of Higher Education, the China Postdoctoral Science Foundation (20080431050 and 200801352), the Training Fund of NENU's Scientific Innovation Project, and the Analysis and Testing Foundation of Northeast Normal University for support. ’ REFERENCES (1) (a) Sun, Y. Q.; Zhang, J.; Chen, Y. M.; Yang, G. Y. Angew. Chem., Int. Ed. 2005, 44, 5814. (b) Hagrman, D.; Haushalter, R. C.; Zubieta, J. Chem. Mater. 1998, 10, 361. (c) Yaghi, O. M.; Li, H. J. Am. Chem. Soc. 1999, 118, 295. (d) Niu, J. Y.; Wu, Q.; Wang, J. P. J. Chem. Soc., Dalton Trans. 2002, 2512. (e) Peng, Z. H. Angew. Chem., Int. Ed. 2004, 43, 930. (f) Lin, Z. E.; Zhang, J.; Zhao, J. T.; Zheng, S. T.; Pan, C. Y.; Wang, G. M.; Yang, G. Y. Angew. Chem., Int. Ed. 2005, 44, 6881. (2) (a) Hagrman, P. J.; Hagrman, D.; Zubieta, J. Angew. Chem., Int. Ed. 1999, 38, 2638. (b) M€uller, A.; Pope, M. T.; Peters, F.; Gatteschi, D. Chem. Rev. 1998, 98, 239. (c) Won, B. K.; Voitl, T.; Rodrıguez-Rivera, G. J.; Dumesic, J. A. Science 2004, 305, 1280. (d) Lin, B.-Z.; Liu, S.-X. Chem. Commun. 2002, 2126. (e) Pan, C.-L.; Xu, J.-Q.; Sun, Y.; Chu, D.-Q.; Ye, L.; L€u, Z.-L.; Wang, T.-G. Inorg. Chem. Commun. 2003, 6, 233. (f) Liu, C.-M.; Luo, J.-L.; Zhang, D.-Q.; Wang, N.-L.; Chen, Z.-J.; Zhu, D.-B. Eur. J. Inorg. Chem. 2004, 4774. (g) M€uller, A.; Krickemeyer, E.; Meyer, J.; B€ogge, H.; Peters, F.; Plass, W.; Diemann, E.; Dillinger, S.; Nonnenbruch, F.; Randerath, M.; Menke, C. Angew. Chem., Int. Ed. 1796


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