Two New Three-Dimensional Porous Polyoxometalates with Typical ACO Topological Open Frameworks: {[Cu4V13IVV5VO42(NO3)(C3H10N2)8]‚10H2O}n and {[Cu4V12IVV6VO42(SO4)(C3H10N2)8]‚10H2O}n
CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 5 925-929
Yan Xu,*,† Lin-Bo Nie,† Dunru Zhu,‡ You Song,§ Guang-Peng Zhou,† and Wan-Sheng You† Institute of Chemistry for Functionalized Materials, College of Chemistry and Chemical Engineering, Liaoning Normal UniVersity, No. 850, Huanghe Road, Dalian, 116029, P. R. China, Department of Chemistry, College of Chemistry and Chemical Engineering, Nanjing UniVersity of Technology, No. 5, New Model Road, Nanjing 210009, P. R. China, and Coordination Chemistry Institute, Nanjing UniVersity, Nanjing 210093, P. R. China ReceiVed NoVember 9, 2006; ReVised Manuscript ReceiVed February 10, 2007
ABSTRACT: Two new three-dimensional open frameworks, {[Cu4V13IVV5VO42(NO3)(C3H10N2)8]‚10H2O}n (1) and {[Cu4V12IVV6VO42(SO4)(C3H10N2)8]‚10H2O}n (2), have been hydrothermally synthesized. Structural analysis indicates that both complexes are isomorphic and are constructed from a cluster anion [V18O42(XOy)]8- (X ) N, y ) 3 or X ) S, y ) 4) and a bridging cation [Cu(C3H10N2)2]2+ with classical ACO topological structure. Complex 1 crystallizes in the tetragonal space group P4/nnc, with a ) b ) 15.1128(12) Å, c ) 18.670(3) Å, V ) 4264.1(9) Å3, Z ) 2. Complex 2 is tetragonal, P4/nnc, a ) b ) 15.1131(10) Å, c ) 18.588(10) Å, V ) 4245.5(7) Å3, Z ) 2. Both complexes keep the same topological framework with channels of dimensions 7.5 × 7.5 Å running along the [001] direction. Introduction Over the past few decades, the synthesis of polyoxometalates has been extensively studied due to their diverse properties, with applications in catalysis, sorption clathration, electrical conductivity, and magnetism.1,2 Moreover, the Keggin-structural polyoxometalates exhibit potential anti-HIV activity, and some of them are under preclinical evaluation for the treatment of HIV. In the past few years, a very important advance in polyoxometalate chemistry has been the study of the assembly of polyoxometalate anions with inorganic or organometallic bridging complexes into extended structures,3-18 on the basis of the remarkable features of metal oxide surfaces and selective adsorption.18 Several reported open framework materials such as [Ni(2,2′-bpy)2[Mo4O13]6 and Cs5[Cr3O(OOCH)6(H2O)3][RCoW12O40]‚7.5H2O18 have been structurally determined to have one-dimensional and three-dimensional (1D and 3D) structures, respectively, while [Cu(en)2(H2O)]{[PMo8VIV6IVO42Cu(en)2][Cu0.5(en)]3}‚5.5H2O16 and K{V12IVV6VO42Cl[Ni(en)2]3}‚8H2O17 are both two-dimensional (2D) structures. One of the strategies used for the design and synthesis of 3D polyoxometalates is to employ a specific coordinated transition metal cation as a charge compensation agent and template. Successful examples include the formation of [{Cu(1,2-pn)2}7{V16O38(H2O)}2]‚4H2O3 in the presence of {Cu(1,2-pn)2}2+ and the synthesis of KH2[(C5H8NO2)4(H2O)Cu3][BW12O40]‚5H2O5 and (N2H5)2[Zn3VIV12VV6O42(SO4)(H2O)12]‚24H2O11 by using [(C5H8NO2)4(H2O)Cu3]3+and [Zn(H2O)4]2+, respectively. Although many metal-organic open frameworks with typical zeolitic topological structures were prepared,19 no typical topological 3D polyoxometalate was reported, due to the difficulty of controlling the terminal oxygen of polyanions bonding bridging transition metal coordination cations. Here, we present the synthesis and structural determination of the first ACO20 topologicalopenframework,designedas{[Cu4V13IVV5VO42* Corresponding author. † Liaoning Normal University. ‡ Nanjing University of Technology. § Nanjing University.
(NO3)(C3H10N2)8]‚10H2O}n (1) and {[Cu4V12IVV6VO42(SO4)(C3H10N2)8]‚10H2O}n (2). [Cu(C3H10N2)2]2+ was used as a bridging cation in the synthesis of this typical zeolitic topological porous polyoxometalate. Experimental Section General Remarks. All chemicals purchased were of reagent grade and used without further purification. The crystalline product was characterized by thermal analysis, powder X-ray diffraction (XRD), single-crystal XRD, and IR spectroscopy. C, H, and N elemental analyses were performed on a Perkin-Elmer 2400 CHN elemental analyzer. Infrared spectra were recorded from KBr pellets on a Nicolet 170SXFT/IR spectrometer. Thermogravimetric analyses (TGA) were carried out on a Diamond TG/DTA instrument (Perkin-Elmer) thermal analyzer under nitrogen atmosphere at a scan rate of 10 °C /min. Synthesis of 1. The hexagon-shaped dark crystals were synthesized by the hydrothermal reaction using V2O5 (0.67 g), SiO2 (0.22 g), Cu(OAC)2‚2H2O (0.67 g), 1,2-diaminopnopane (1.37 g), and H2O (2.00 g) in a molar ratio of 1:1:1:5:30. The mixture was neutralized to pH ) 6.0 with 25% HNO3 and then placed into a 25 mL Teflon-lined autoclave and heated at 160 °C for 7 days. After the sample was cooled to room temperature, washed with distilled water, filtered, and dried in air, hexagon-shaped dark crystals were obtained (0.68 g, yield 62.5% based on V). In addition, we also tried to synthesize this complex without SiO2, but the yield was low (42.5%) and the quality of crystal was poor. Analysis found: C, 10.67; N, 8.78; H, 3.96% (Calc.: C, 10.74; N, 8.87; H, 3.88%). IR spectra were recorded on a Bruker AXS FT-IR spectrophotometer (range: 400-4000 cm-1) from KBr pellets. IR: ν ) 1564(m), 1440(w), 1370(w), 1042(m), 1020(m), 970(s), and 686 (s) cm-1. Synthesis of 2. The mixture of V2O5 (0.67 g), SiO2 (0.22 g), Cu(OAC)2‚2H2O (0.67 g), 1,2-diaminopnopane (1.39 g), and H2O (2.01 g) in a molar ratio 1:1:1:5:30 was neutralized to pH ) 6.5 with 25% H2SO4 and then placed into a 25 mL Teflon-lined autoclave and heated at 160 °C for 7 days. After the sample was cooled to room temperature, hexagon-shaped dark crystals were obtained (0.59 g, yield 53.2% based on V). In addition, 2 was successfully synthesized without SiO2 but with a low yield (34.7%) and poor quality of single crystal. Analysis found: C, 10.56; N, 8.32; H, 3.86, S, 1.12% (Calc.: C, 10.62; N, 8.26; H, 3.69; S, 1.17%). IR: ν ) 1596(m), 1456(w), 1379(w), 1055(m), 1025(m), 976(s), and 681(s) cm-1. X-ray Crystallography. Crystal data for 1: C24H100N17Cu4O55V18, Mr ) 2678.29, tetragonal, space group P4/nnc, a ) b ) 15.1128(12) Å, c ) 18.670(3) Å, V ) 4264.1(9) Å3, Z ) 2, T ) 293(2) K, F(000)
10.1021/cg0607912 CCC: $37.00 © 2007 American Chemical Society Published on Web 03/30/2007
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Table 1. Crystal Data and Structure Refinements for 1 and 2 empirical formula fw T (K) λ (Å) crystal system space group a (Å) c (Å) V (Å3) Z Dc (g/cm3) µ (mm-1) GOF on F2 R1 [I > 2σ(I)]a wR2 [I > 2σ(I)] a
1
2
{[Cu4V13IVV5VO42(NO3)(C3H10N2)8]‚10H2O}n 2678.29 293(2) 0.71073 tetragonal P4/nnc 15.1128(12) 18.670(3) 4264.1(9) 2 2.086 2.945 1.032 0.0639 0.1763
{[Cu4V12IVV6VO42(SO4)(C3H10N2)8]‚10H2O} 2712.34 293(2) 0.71073 tetragonal P4/nnc 15.1131(10) 18.588(2) 4245.5(7) 2 2.122 2.893 1.058 0.0892 0.2369
R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) ∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]1/2.
Figure 1. The structure of the building unit of open framework 1 [V13IVV5VO42(NO3)]8- connects eight µ2-{Cu(C3H10N2)2} bridges.
Figure 2. The [NO3]- anion is adapted to high symmetry by using disorder.
Figure 3. (a) View of the 3D structure of 1 along the c-axis. (b) ACO topological structure of 1. (c) Polyhedral view of the framework along the c-axis.
) 2666, λ(Mo-KR) ) 0.71073 Å, hexagon-shaped dark crystal, 20 275 reflections collected, 1555 independent, 162 parameters, R1 ) 0.0639, wR2 ) 0.1763, GOF ) 1.032. Crystal dimensions of 0.12 × 0.12 × 0.10 mm3.
Crystal Data for 2. C24H100N16Cu4O56SV18, Mr ) 2712.34, tetragonal, space group P4/nnc, a ) b ) 15.1131(10) Å, c ) 18.588(2) Å, V ) 4245.5(7) Å3, Z ) 2, T ) 293(2) K, F(000) ) 2700, λ(Mo-KR) ) 0.71073 Å, hexagon-shaped dark crystal, 13 075 reflections collected,
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Figure 4. The second building unit of open framework 1 (C, H, N atoms were omitted); each polyanion connects eight adjacent polyanions.
Figure 5. The structure of polyanion of 2 (disordered SO42- is surrounded). 1190 independent, 155 parameters, R1 ) 0.0892, wR2 ) 0.2369, GOF ) 1.058, crystal dimensions of 0.10 × 0.10 × 0.09 mm3. Crystal structure determinations by X-ray diffraction for complexes 1 and 2 were performed on a Bruker Apex 2 CCD diffractometer with graphite-monochromated Mo-KR (λ ) 0.71073 Å) radiation at room temperature. An empirical absorption correction was applied. The hydrogen atoms in both structures were refined in calculated positions, assigned isotropic thermal parameters, and allowed to ride their parent atoms. The [NO3]- anion in 1 is adapted to high symmetry by using disorder. The occupied factors for O7 and O8 are 0.5 and 0.25. Similarly, the [SO4]2- in 2 is also disordered with half-occupied O7. All calculations were performed using the SHELX97 program package. A summary of the crystallographic data and structural determination for complexes 1 and 2 is provided in Table 1.
Results and Discussion Synthesis. The hydrothermal technique has recently been demonstrated to be a powerful method in the synthesis of 3D zeolitic materials. In a specific hydrothermal synthesis, many factors can affect the nucleation and crystal growth of products, such as the type of starting concentrations, initial reactants, pH values, solvents, reaction time, and temperature. In our case, the pH value of the reaction system was of crucial importance for the formation of final products. Other products can be synthesized from the same initial reactants with different pH values. The coordination [Cu(C3H10N2)2]2+ cation is also important for the formation of the framework, due to controlling the connection of polyanions. Crystal Structures of Compounds. Single-crystal X-ray structural analysis reveals that the 3D structure of 1 kept the
Figure 6. EPR spectra for 1 (a) and 2 (b) at room temperature.
ACO topological open framework and consisted of polyanion [V13IVV5VO42(NO3)] cages and [Cu(C3H10N2)2]2+ bridging groups. As shown in Figure 1, such as the double 4-membered ring (D4R) in CoPO4,20 each polyanion [V13IVV5VO42(NO3)] cage is connected to eight neighboring units through [Cu(C3H10N2)2]2+ bridging groups to generate a new ACO topological 3D framework of {[Cu4V13IVV5VO42(NO3)(C3H10N2)8]‚ 10H2O}n. Complex 1 represents a most unusual member of octodecavanadates with the encapsulated [NO3]- anion. Compared with other [V18O42]n- cages, all cages are found to contain the center of XO4 (X ) V, S)13 or X (X ) Cl)17. The building unit [V13IVV5VO42(NO3)]8- exhibits only one type of coordination model for V atoms: tetragonal pyramids VO5. The host shell {V13IVV5VO42} is constructed from 18 VO5 square pyramids by sharing the edges through 24 bridging oxygen atoms. The polyanion [V13IVV5VO42(NO3)]8- lies on a crystallographic 4-fold axis at 0.25, 0.25, Z, which possesses the central [NO3]- anion. To the best of our knowledge, the [V18O42(NO3)]8cluster anion in 1 represents the first observation of an octadecavanadium cluster with [NO3]- at the center as a guest in vanadate chemistry. As shown in Figure 2, the [NO3]- anion
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Figure 7. (a) Experimental and (b) simulated XRD patterns of 1. (c) Experimental and (d) simulated XRD patterns of 2.
is adapted to high symmetry by using disorder. The occupied factors for O7 and O8 are 0.5 and 0.25. The V_O distances are between 1.598(4) and 1.957(3) Å, while the O-V-O angles vary from 80.06(14) to 149.96(14)°, which are comparable to the reported vanadates data. The six-coordinated Cu cation is completed by four N atoms of 1,2-diaminopnopane and two O atoms from two polyanions units, forming an octahedral geometry structure. The Cu-O bond length in the octahedra is 2.436(3) Å, similar to that of the previously reported compounds [Cu(en) 2 (H 2 O)]{[PMo 8 VI V 6 IV O 42 Cu(en) 2 ][Cu 0.5 (en)] 3 }‚ 5.5H2O16 and [{Cu(1,2-pn)2}7{V16O38(H2O)}2]‚4H2O,3 while the bond angle of V-O-Cu is 128.2(2)°, in accordance with the Co-O-P bond angle of CoPO4.20 In the ACO topological framework of CoPO4, each µ2-oxygen atom connects two D4R units, while each D4R unit links eight neighboring D4R units through eight µ2-oxygen atoms. Similarly, in the open framework of 1 (Figure 3), every µ2-briging group {Cu(C3H10N2)2} connectstwopolyanions{V13IVV5VO42},whileeach{V13IVV5VO42} anion connects eight adjacent {V13IVV5VO42} units through eight µ2-{Cu(C3H10N2)2} groups (Figure 4). A µ-oxygen O3 links the polyanion {V13IVV5VO42} and Cu1; the V1-O3 distance [1.681(3) Å] is longer than the other V-Ot bond lengths [1.598(4) to 1.631(7) Å] but shorter than V-Ob [1.892(4)-1.957(3) Å ] in the open framework of 1. Compared with CoPO4, the building unit {V13IVV5VO42} and bridging group µ2-{Cu(C3H10N2)2} are much bigger than the unit D4R (P4Co4O12) and µ2-O; correspondingly, 14-membered ring channels are generated in the open framework of 1 (eight-membered ring channels for CoPO4). The narrowest diameter of the 14-membered channel is about 7.5 Å. The guest water molecules are involved in hydrogen bonds with the open framework in 1, and the shortest
distance between water and oxygen from the framework is 2.84(2) Å. The assignment of the oxidation state for vanadium are in accordance with their coordination geometries and are confirmed by electron spin resonance (ESR) spectra and valence sum calculations,21 which give the values of 4.120 for V1, 4.497 for V2, and 4.257 for V3. The average value is 4.303, which is very close to the expected value of 4.278 for V13IVV5V. By replacing HNO3 (25%) by H2SO4 (25%) in a hydrothermal reaction similar to that of complex 1, we obtained {[Cu4V12IVV6VO42(SO4)(C3H10N2)8]‚10H2O}n 2. The polyanion [V18O42(SO4)]n- has been reported by Khan,11 in which each polyanion is connected by six transition metal (Zn) atoms through bridging O atoms. Similar with 1, complex 2 keeps the same ACO topological structure, in which each polyanoin [V18O42(SO4)]n- is bonded by eight Cu2+ cations. As shown in Figure 5, the polyanion [V18O42(SO4)]8- lies on a crystallographic 4-fold axis at 0.25, 0.25, Z, which possesses the central [SO4]2- anion that is disordered with half-occupied O atoms (O7 and its crystallographic partners). Compared with 1, in the structure of 2 the bridging O3 atom is closer to the Cu ion. The bond distance for V1-O3 is 1.768(4) Å, which is 0.087 Å longer than the V1-O3 bond length in 1. The electron EPR spectra of 1 and 2 were measured at room temperature (Figure 6), and both compounds exhibited widened peaks. The signals for V4+ for 1 and 2 were observed, and the g parameters calculated from both EPR spectra are 1.97 and 1.96, respectively. The experimental and simulated XRD patterns of 1 and 2 are shown in Figure 7. The peak positions are in agreement with each other, which indicates the phase purity of both complexes 1 and 2. The intensity of the experimental XRD
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(C3H10N2)8]‚10H2O}n (2), have been hydrothermally synthesized. The synthesis of both complexes demonstrates that the polyanions can be used as building units of typical zeolitic open frameworks through the choice of polyanions and bridging groups. The present work has great significance for the chemistry of polyoxometalates and porous materials. Acknowledgment. The authors thank the Education Office Foundation of Liaoning province (05L220) for financial support. References
Figure 8. (a) TG curve of 1. (b) TG curve of 2.
patterns are a little weak, due to the preferred orientation of the powder samples and the instrumental limitations. TG Analyses. Thermogravimetric analysis (TGA) of complex 1 reveals a total weight loss of 28.8% in the range of 50-900 °C, which agrees with the calculated value of 29.5%. The weight loss of 6.9% in the range of 50-160 °C corresponds to the loss of lattice water molecules (calcd 6.7%), whereas the weight loss of 21.9% in the range of 160-900 °C (Figure 8a) arises from the loss of 1,2-diaminopnopane and NO2 (calcd 22.7%). Similarly, the TG curve of 2 (Figure 8b) exhibits a total weight loss of 29.8% in the range of 50-900 °C, which agrees with the calculated value of 31.4%. The weight loss of 6.7% in the range of 50-160 °C corresponds to the loss of lattice water molecules (calcd 6.6%), whereas the weight loss of 23.1% in the range of 160-900 °C arises from the loss of 1,2diaminopnopane and SO3 (calcd 22.6%) Conclusions Inconclusion, two new 3D open frameworks,{[Cu4V13IVV5VO42(NO3)(C3H10N2)8]‚10H2O}n (1) and {[Cu4V12IVV6VO42(SO4)-
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