Inorganic−Organic Hybrid Materials Containing Porous Frameworks

Chem. Mater. 2004, 16, 5273-5279

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Inorganic-Organic Hybrid Materials Containing Porous Frameworks: Synthesis, Characterization, and Magnetic Properties of the Open Framework Solids [{Co(4,4′-Bipy)}V2O6] and [{Co2(4,4′-Bipy)3(H2O)2}V4O12]‚2H2O M. Ishaque Khan,*,† Elizabeth Yohannes,† Renata C. Nome,† Samar Ayesh,† Vladimir O. Golub,‡ Charles J. O’Connor,‡ and Robert J. Doedens*,§ Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, Chicago, Illinois 60616, Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, and Department of Chemistry, University of California, Irvine, California 92697 Received June 10, 2004. Revised Manuscript Received October 1, 2004

Synthesis of two novel porous framework hybrid materials, [Co(4,4′-bipy)V2O6] (1) and [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2), and their characterization by infrared spectroscopy, thermogravimetry, elemental analysis, manganometric titration, surface area measurement, bond valence sum calculations, temperature-dependent magnetic susceptibility measurement, and single-crystal X-ray structure analyses is described. Both compounds exhibit remarkable thermal stability. The three-dimensional structures of 1 and 2 are composed of fused {VO4} motifs linked by {Co(4,4′-bipy)} coordination polymers. The structure of 1 is comprised of {CoO3N2} trigonal bipyramids, linked in two dimensions by corner-sharing {VO4} tetrahedra and in the third dimension by the 4,4′-bipyridine ligands. In the bimetallic layers, the cobalt centers are bridged alternately by {VO4} and {V2O7} units, generating alternating eightmembered {Co2V2O4} and twelve-membered {Co2V4O6} rings. The crystal structure of 2 consists of a novel three-dimensional network containing two types of octahedral Co2+ ions linked by a {V2O7} group. The cobalt centers in 2 are linked in three dimensions by bridging 4,4′-bipyridine ligands. The structure contains rather large channels parallel to the c-axis. A disordered water molecule of crystallization is present in the channels. Crystal data for C10H8N2O6CoV2, 1: triclinic space group P1 h (No. 2), a ) 8.1517(4) Å, b ) 8.5794(4) Å, c ) 10.1233(5) Å, R ) 87.0170(10)°, β ) 75.9610(10)°, γ ) 75.1740(10)°, V ) 663.94(6) Å3, Z ) 2, Dcalcd ) 2.066 Mg‚m-3, R1 ) 0.0252 (all data), wR2 ) 0.0669. Crystal data for C15H16N3O8CoV2, 2: monoclinic space group C2/c (No. 15), a ) 30.4457(13) Å, b ) 11.3540(5) Å, c ) 11.5836(5) Å, β ) 106.5390(10)°, V ) 3838.6(3) Å3, Z ) 8, Dcalcd ) 1.824 Mg‚m-3, final R1 ) 0.0447 (all data), wR2 ) 0.1259.

Introduction The design and synthesis of composite materials is of contemporary interest.1-4 Composites are likely to exhibit improved properties and functions unobserved in purely inorganic or organic phases. In view of the outstanding catalytic and sorbtive properties exhibited by conventional zeolites, which contain rigid porous framework structures composed of corner-sharing aluminosilicate tetrahedra, there has been increased interest in the development of porous framework inorganic* Corresponding authors. E-mail: [email protected]. † Illinois Institute of Technology. ‡ University of New Orleans. § University of California, Irvine. (1) Cheng, C.; Fu, S.; Yang, C.; Chen, W.; Lin, K.; Lee, G.; Wang, Y. Angew. Chem., Int. Ed. 2003, 42, 1937. (2) Sanchez, C.; Soler-Illia, G. J. A.; Ribot, F.; Lalot, T.; Mayer, C. R.; Cabuil, V. Chem. Mater. 2001, 13, 3061. (3) Xu, B.; Wei, Y.; Barnes, C.; Peng, Z. Angew. Chem., Int. Ed. 2001, 40, 2290. (4) Ferey, G. Chem. Mater. 2001, 13, 3084.

organic hybrid materials containing zeolitic channels and cavities. Conceptually, such materials might exhibit catalytic, sorbtive, and electronic properties unobserved in conventional zeolites. An impressive new class of metal-organic porous framework solids5-8 have been prepared by the “modular chemistry” approach9 which exploits secondary building units, which have been widely regarded as the organizing principle for the framework structures in (5) Yaghi, O. M.; Li, H.; Davis, C.; Richardson, D.; Groy, T. L. Acc. Chem. Res. 1998, 31, 474-484 and references therein. (6) Eddaoudi, M.; Moler, D.; Li, H.; Chen, B.; Reineke, T.; O’Keeffe, M.; Yaghi, O. Acc. Chem. Res. 2001, 34, 319-330 and references therein. (7) Eddaoudi, M.; Li, H.; Yaghi, O. M. J. Am. Chem. Soc. 2000, 122, 1391-1397. (8) Chen, B.; Eddaoudi, M.; Hyde, S.; O’Keeffe, M.; Yaghi, O. Science 2001, 291, 1021-1023. (9) Modular Chemistry; Michl, J., Ed.; Kluwer Academic Publishers: Dordrecht, 1995, and references therein. (10) Dyer, A. An Introduction to Zeolite Molecular Sieves; Wiley: New York, 1988.

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conventional zeolites,10,11 as the basis for assembling extended solids. The secondary building units in these porous metal-organic framework structures are generated by combining simple metal ions with polytopic organic ligands such as 1,3,5,7-adamantanetetracarboxylate. Another useful synthetic approach to composite solids involves combination of metal oxides with organic ligands along with other heterometal centers. This has yielded another major class of organic-transition metal oxide hybrids constructed from molybdenum oxide motifs and metal-organic complexes.12-15 We are currently exploring the design and development of open framework composites by the amalgamation of vanadium oxide based structures with metalorganic compounds and their coordination polymers.17-21 Unlike aluminosilicates, vanadium-based frameworks exhibit a variety of metal oxidation states, variable coordination numbers, and diverse geometries around the vanadium. These features could provide a basis for new types of catalytic behavior. The tetrahedral {VO4} unit, which is commonly observed in aqueous solutions and has a topology analogous to that of tetrahedral {SiO4} and {AlO4} units in aluminosilicates, provides a potentially versatile motif for constructing oxovanadate-based zeolitic solids. Transition metal oxide based zeolitic materials, which are practically unknown at present, may combine the shape selectivity of conventional zeolites with the reactivity and redox properties of transition metals. During this ongoing effort16-20 we have discovered new porous framework materials of unprecedented structures composed of vanadium oxide and metal-organoamine coordination polymers. Here we describe the synthesis of two novel open framework hybrid materials, [Co(4,4′-bipy)V2O6] (1) and [{Co2(4,4′bipy)3(H2O)2}V4O12]‚2H2O (2), and their characterization by infrared spectroscopy, thermogravimetry, elemental analysis, manganometric titration, surface area (11) Barrer, R. M. Hydrothermal Chemistry of Zeolites; Academic Press: London, 1982. (12) Hagrman, D.; Warren, C. J.; Haushalter, R. C.; Seip, C.; O’Connor, C. J.; Rarig, J. R. L.; Johnson, K. M.; Laduca, J. R. L.; Zubieta, J. Chem. Mater. 1998, 10, 3294. (13) Hagrman, P. J.; Hagrman, D.; Zubieta, J. Angew. Chem., Int. Ed. 1999, 38, 2638-2684 and references therein. (14) Zapf, P. J.; Warren, C. J.; Haushalter, R. C.; Zubieta, J. Chem. Commun. 1997, 1543. (15) (a) Hagrman, D.; Haushalter, R. C.; Zubieta, J. Chem. Mater. 1998, 10, 361. (b) Hagrman, D.; Zubieta, J. J. Solid State Chem. 2000, 152, 141. (c) Hagrman, D.; Zubieta, C.; Rose, D. J.; Zubieta, J. Angew. Chem., Int. Ed. 1997, 36, 873. (d) Hagrman, D.; Zubieta, J. Chem. Commun. 1998, 2005-2006. (e) Zapf, P. J.; Hammond, R. P.; Haushalter, R. C.; Zubieta, J. Chem. Mater. 1998, 10, 1366-1373. (16) (a) Khan, M. I.; Cevik, S.; Doedens, R. In Polyoxometalate Chemistry for Nano-Composite Design; Yamase, T., Pope, M. T., Eds.; Kluwer Academic: New York, 2002; pp 27-38. (b) Khan, M. I.; Yohannes, E.; Ayesh, S.; Doedens, R. J. J. Mol. Struct. 2003, 656, 4553. (c) Khan, M. I.; Yohannes, E.; Doedens, R. J. Inorg. Chem. 2003, 42, 3125-3129. (17) (a) Khan, M. I.; Cevik, S.; Powell, D.; Li, S.; O’Connor, C. J. Inorg. Chem. 1998, 37, 81-86. (b) Khan, M. I.; Cevik, S.; Doedens, R. J. Chem Soc., Chem. Commun. 2001, 1930-1931. (18) (a) Khan, M. I.; Tabussum, S.; Doedens, R. J. Chem. Commun. 2003, 532-533. (b) Khan, M. I.; Tabussum, S.; Doedens, R. J.; Golub, V. O.; O’Connor, C. J. Inorg. Chem. Commun. 2004, 7, 54. (c) Khan, M. I.; Hope, T.; Cevik, S.; Zheng, C.; Powell, D. J. Cluster Sci. 2000, 11, 433-447. (19) (a) Khan, M. I. J. Solid State Chem. 2000, 152, 105. (b) Khan, M. I.; Yohannes, E.; Doedens, R. J. Angew. Chem., Int. Ed. 1999, 38, 1292. (20) Khan, M. I.; Deb, S.; Nome, R.; Yohannes, E.; Cevik, S.; Doedens, R. Unpublished work.

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measurement, bond valence sum calculations, temperature-dependent magnetic susceptibility measurement, and single-crystal X-ray structure analyses. Experimental Section Materials and Methods. Commercially available reagent grade chemicals were purchased from Sigma-Aldrich, Fischer, Cerac, and Alfa Aesar. These were used without further purification. All synthetic reactions were carried out in 23mL Parr Teflon-lined acid digestion bombs. While only the best preparation methods leading to high purity, high yield, and superior crystal quality for each of the reported compounds is described here, many reactions with varying reaction conditions (stoichiometry, reaction time, and temperatures) were studied in each case. Infrared spectra of the compounds were recorded on a Thermonicolet Nexus 470 or Perkin-Elmer Paragon 1000 infrared spectrometer (KBr pellets in 400-4000 cm-1 region). The spectra were evaluated using Thermonicolet’s OMNIC software. The thermogravimetric analyses of the compounds were performed on either a Universal V2.5H thermal analyzer or a Mettler-Toledo TGA/SDTA 851E instrument and the results were analyzed using Mettler Toledo STAR 7.01 software. Samples were placed in a quartz bucket or 70-µL alumina pan and heated in the temperature range 25-800 °C at a rate of 5 °C/min in nitrogen atmosphere with a flow rate of 60-90 mL/min. The residues from TGA experiments were examined by IR spectroscopy. BET surface area measurement was performed on a 0.3160-g sample of 2 using nitrogen physisorption method on a Micromeritics ASAP 2010 instrument. X-ray powder diffraction patterns for a heated sample of 2 were obtained on a Siemens D5000 powder XRD system at room temperature between 5 and 80° 2θ at 3 s count for every 0.02 degrees. The magnetic data were recorded on a 13.24-mg of sample of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O in the 2-300 K temperature range using a Quantum Design MPMS-5S SQUID spectrometer. The magnetic data were also recorded on 17.31 mg of a heated (at 234 °C in He stream) polycrystalline sample of [Co2(4,4′-bipy)3(H2O)2][V4O12]‚2H2O, in the 2-300 K temperature range. The temperature-dependent magnetic data were obtained at a magnetic field H ) 1000 Oe. Calibrating and operating procedures were carried out according to the literature method.21 Crystal Structure Analyses. Single-crystal structure analyses were carried out at 173 K for 1 and 2. Crystals were immersed in Paratone hydrocarbon oil and mounted on glass fibers in a cold nitrogen stream on a Bruker SMART CCD diffractometer. Experimental details are summarized as follows;22 full details are available as Supporting Information. Data were collected on a Bruker SMART-CCD diffractometer23 at T ) 173 K with graphite monochromatized Mo KR radiation (λ ) 0.71073 Å) and processed with SAINT.24 Structures were solved by direct methods and refined by fullmatrix least squares on F2 (SHELXTL Version 5.10).25 Absorption corrections were calculated by use of SADABS.26 Nonhydrogen atoms were refined anisotropically, with the exception of the disordered water oxygen atom in 2; hydrogen atoms were included at idealized positions and refined by use of the riding model. Crystal data for C10H8N2O6CoV2, 1: crystal dimensions (21) O’Connor, C. J. Prog. Inorg. Chem. 1979, 29, 203. (22) Further details of the structure determination are available on request from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK (e-mail: [email protected]) by quoting the depository numbers CCDC 237526 and CCDC 237525 (http://www.ccdc.cam.ac.uk). (23) SMART, Version 4.210; Simens Analytical X-ray Systems: Madison, WI, 1997. (24) SAINT, Version 4.050; Simens Analytical X-ray Systems: Madison, WI, 1995. (25) Sheldrick, G. M. SHELXTL Version 5.1; Siemens Industrial Automation, Inc.: Madison, WI ,1995. (26) Sheldrick, G. M. SADABS; University of Gottingen: Gottingen, Germany, 1997.

Open-Framework Hybrid Metal-Organic Materials 0.43 × 0.25 × 0.17 mm3, triclinic space group P1 h (No. 2), a ) 8.1517(4) Å, b ) 8.5794(4) Å, c ) 10.1233(5) Å, R ) 87.0170(10)°, β ) 75.9610(10)°, γ ) 75.1740(10)°, V ) 663.94(6) Å3, Z ) 2, Fcalcd ) 2.066 Mg‚m-3, µ(Mo KR) ) 2.640 mm-1, min/max transmission ) 0.702. Of the 6894 reflections measured (2.07° e θ e 28.27°), 3068 independent reflections were used to solve and refine the structure. Based on all data and 190 refined parameters, final R1 ) 0.0252, wR2 ) 0.0669, and the goodness-of-fit on F2 ) 1.064. Crystal data for C15H16N3O8CoV2, 2: crystal dimensions 0.45 × 0.22 × 0.11 mm3, monoclinic space group C2/c (No. 14), a ) 30.4457(13) Å, b ) 11.3540(5) Å, c ) 11.5836(5) Å, β ) 106.5390(10)°, V ) 3838.6(3) Å3, Z ) 8, Fcalcd ) 1.824 Mg‚m-3, µ(Mo KR) ) 1.857 mm-1, min/max transmission ) 0.803. Of the 18787 reflections measured (1.92° e θ e 28.28°), 4544 independent reflections were used to solve and refine the structure. Based on all data and 271 refined parameters, final R1 ) 0.0447, wR2 ) 0.1259, and the goodness-of-fit on F2 ) 1.161. In accord with the elemental analysis of 2, the sum of the occupancies of the oxygen atoms of the disordered water molecule in the channel was constrained to 1.0; also, the thermal parameters of these partial oxygen atoms were constrained to be equal. Synthesis of [{Co(4,4′-bipy)}(V2O6)] (1). A mixture consisting of NaVO3 (1.25 mmol), 4,4′-bipyridine (1.25 mmol), CoSO4‚7H2O (1.25 mmol), and H2O (555.5 mmol) in the molar ratio of 1:1:1:444 was placed in a 23-mL Parr Teflon-lined autoclave. After the mixture was stirred for 30 s the autoclave was sealed and heated for 72 h in an electric furnace maintained at 160 °C. After the autoclave was cooled at room temperature for 2 h, dark brown prismatic crystals mixed with golden yellow crystals (minor product, ∼10%) were filtered from the colorless mother liquor. The crystalline mixture was washed thoroughly with methanol and then rinsed with deionized water and dried in air at room temperature. The brown crystals of 1 were mechanically separated from the yellow crystals [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2), to give 165 mg (∼64% based on vanadium) of the major product [Co(4,4′-bipy)V2O6]. Anal. Calcd: Co, 14.27; V, 24.67. Found: Co, 11.77; V, 25.19. Prominent IR bands (KBr pellet, 4000-400 cm-1), 1608 (s), 1534 (m), 1489 (m), 1412 (s), 1322 (w), 1219 (s), 1074 (m), 1012 (m), 961 (vs), 935 (sh), 908 (vs), 856 (sh), 789 (vs), 690 (sh), 635 (m), 569 (m), 509(m). Synthesis of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2). The yield of the golden yellow compound, 2, observed as minor product in the above-described synthesis of 1 could be increased by the following modified procedures. Method I. A mixture consisting of V2O5 (1.25 mmol), LiOH‚ H2O (2.5 mmol), 4,4′-bipyridine (1.87 mmol), tetrabutylammonium bromide (1.25 mmol), CoSO4‚7H2O (2.5 mmol), and H2O (666.66 mmol) in the molar ratio of 1:2:1.5:1:2:533 was placed in a 23-mL Teflon-lined Parr autoclave, which was heated for 72 h in an electric furnace maintained at 135 °C. After the autoclave was cooled at room temperature for 2 h, golden yellow needle-shaped crystals of 2 mixed with the dark brown prismatic crystals of 1 and a brown needle-shaped microcrystalline material of an incompletely characterized impurity were filtered from the light yellow mother liquor. The crystalline mixture was washed thoroughly with methanol and deionized water and dried in air at room temperature. The three component mixture was separated mechanically to give 110 mg (∼17% based on vanadium) of golden yellow needles of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2), 50 mg (∼10%) of the dark brown prismatic crystals of [Co(4,4′-bipy)V2O6] 1, and 30 mg of the brown needle-shaped microcrystals that have not been fully characterized. Anal. Calcd: C, 34.18; H, 3.06; N, 7.97; V, 19.32. Found: C, 35.35; H, 3.04; N, 8.25; V, 19.30. Prominent IR bands (KBr pellet, 4000-400 cm-1), 1595(s), 1530 (m), 1479(w), 1402(s), 1317(w), 1211(m), 1067(m), 954(s), 899(m), 816(s), 634(vs), 503(w). Method II. The following rationalized synthetic approach gives X-ray diffraction quality crystals of 2 in pure monophasic form and good yield. A mixture consisting of NH4VO3 (1.25 mmol), LiOH‚H2O (2.5 mmol), 4,4′-bipyridine (1.87 mmol), CoSO4‚7H2O (1.87 mmol), and H2O (555.55 mmol) in the molar

Chem. Mater., Vol. 16, No. 25, 2004 5275 ratio of 1:2:1.5:1.5:444 was placed in a 23-mL Teflon-lined Parr autoclave which was heated for 5.75 days in an electric furnace maintained at 135 °C. After the autoclave was cooled at room temperature for 3 h, golden yellow needle-shaped crystals that separated were filtered from the light yellow mother liquor. The crystals were washed with water and dried in air at room temperature to give high-purity X-ray quality crystals of 2 in 60% yield (based on vanadium).

Results and Discussion The hydrothermal reaction of NaVO3, 4,4′-bipyridine, CoSO4‚7H2O, and H2O in the molar ratio of 1:1:1:444 at 160 °C for 72 h yields a mixture of dark brown prismatic crystals of [Co(4,4′-bipy)V2O6] (1) and golden yellow needles of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2). This synthetic procedure gave a good yield (64%) of 1 but a relatively modest yield (10%) of 2. Modification of the reaction conditions (Method I) increased the yield of 2. This procedure, however, produced only marginal quality crystals of 2 and it also produced a small amount of brown needle-shaped microcrystals of an incompletely characterized compound mixed with the crystals of 1. Our attempts to produce X-ray quality single crystals of the microcrystalline impurity have been unsuccessful. Usually, it is difficult to optimize the reaction parameters of the hydrothermal reactions because the reaction system is closed. However, with knowledge of the composition and crystal structures of the compounds it is sometimes possible to predict the limiting reaction parameters that affect the yield of the product. Thus, after the initial characterization of the golden yellow crystals of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2) we were able to prepare it in monophasic form and high yield by using the appropriate stoichiometric ratio of cobalt and 4,4′-bipyridine in the reaction. A rationalized synthesis (Method II) that involved increasing the reaction time and eliminating tetrabutylammonium bromide (which does not appear in the product) from the reaction mixture produced X-ray quality crystals of 2. During the course of effort to improve the yield and purity of these compounds, we carried out a large number of reactions to see the effect of various reaction parameters on the products. We found that the syntheses of these materials are affected not only by the stoichiometries of the reactants but also by the pH of the reaction media, temperature, reaction time, and types of co-ligands in the reaction medium. Because of the need to compromise these effects on the reaction outcome, the actual stoichiometric ratio used in the synthesis may not always agree with the stoichiometric ratio of the balanced equation. Besides forming discrete polyoxovanadate clusters, vanadium is known to make oxovanadate-based chains and layers that contain various combinations of {VOx} (x ) 4, 5, 6) polyhedra.27 Open framework structure solids could, in principle, be made by assembling oxovanadate chains and/or layers around suitable structuredirecting templates.28 A problem with this approach is (27) (a) Pope, M. T. Heteropoly and Isopoly Oxometalates; Springer: Berlin, 1983. (b) Hawthorne, F. C. J. Solid State Chem. 1997, 22, 157-170. (28) (a) Koene, B.; Taylor, N.; Nazar, L. Angew. Chem., Int. Ed. 1999, 38, 2888-2891 and references therein. (b) Shan, Y.; Huang, R.; Huang, S. Angew. Chem., Int. Ed. 1999, 38, 1751-1754. (c) Khan, M. I., et al. Synthesis and structure of [Co(en)3{V3O9}], unpublished result.

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Table 1. Atomic Coordinates (× 104) and Equivalent Isotropic Displacement Parameters (Å2 × 103) for 1 Co(1) V(1) V(2) O(1) O(2) O(3) O(4) O(5) O(6) N(1) N(2) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10)

x

y

z

U(eq)a

8437(1) 12312(1) 6262(1) 10405(2) 12178(2) 7287(2) 3951(2) 6509(2) 7183(2) 6668(2) 206(2) 6723(3) 5507(3) 4169(2) 4117(3) 5374(3) 2810(2) 2116(3) 833(3) 877(3) 2152(3)

8391(1) 7265(1) 5900(1) 7056(2) 9214(2) 6976(2) 6436(2) 6296(2) 3776(2) 8359(2) 8458(2) 7027(2) 6967(2) 8336(2) 9714(2) 9668(2) 8356(2) 7037(2) 7140(2) 9729(3) 9734(3)

4421(1) 5302(1) 3019(1) 5130(2) 5474(1) 3705(1) 3846(2) 1413(1) 3222(1) 6341(2) 12487(2) 7109(2) 8327(2) 8790(2) 7998(2) 6794(2) 10072(2) 10483(2) 11680(2) 12080(2) 10901(2)

11(1) 12(1) 11(1) 19(1) 19(1) 18(1) 19(1) 21(1) 18(1) 14(1) 16(1) 17(1) 17(1) 15(1) 19(1) 18(1) 15(1) 20(1) 21(1) 23(1) 23(1)

a U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor.

Table 2. Selected Bond Lengths [Å] and Angles [deg] for 1a Co(1)-O(3) Co(1)-O(1) Co(1)-O(2)#1 Co(1)-N(1) Co(1)-N(2)#2 V(1)-O(1) V(1)-O(2) V(1)-O(4)#3 V(1)-O(6)#4 V(2)-O(5) V(2)-O(3) V(2)-O(6) V(2)-O(4)

1.9701(14) 1.9831(14) 1.9884(14) 2.1242(16) 2.1392(16) 1.6597(14) 1.6637(14) 1.7694(14) 1.7810(14) 1.6178(14) 1.6666(14) 1.8061(14) 1.8144(14)

O(3)-Co(1)-O(1) 109.52(6) O(3)-Co(1)-O(2)#1 128.86(6) O(1)-Co(1)-O(2)#1 121.61(6) O(3)-Co(1)-N(1) 88.35(6) O(1)-Co(1)-N(1) 91.17(6) O(2)#1-Co(1)-N(1) 89.29(6) O(3)-Co(1)-N(2)#2 92.05(6)

O(1)-Co(1)-N(2)#2 O(2)#1-Co(1)-N(2)#2 N(1)-Co(1)-N(2)#2 O(1)-V(1)-O(2) O(1)-V(1)-O(4)#3 O(2)-V(1)-O(4)#3 O(1)-V(1)-O(6)#4 O(2)-V(1)-O(6)#4 O(4)#3-V(1)-O(6)#4 O(5)-V(2)-O(3) O(5)-V(2)-O(6) O(3)-V(2)-O(6) O(5)-V(2)-O(4) O(3)-V(2)-O(4) O(6)-V(2)-O(4) V(1)-O(1)-Co(1) V(1)-O(2)-Co(1)#1 V(2)-O(3)-Co(1) V(1)#5-O(4)-V(2) V(1)#4-O(6)-V(2)

89.32(6) 89.95(6) 179.23(6) 108.99(7) 108.95(7) 110.67(7) 109.59(7) 109.21(7) 109.41(7) 109.20(8) 109.16(7) 109.69(7) 109.17(7) 109.44(7) 110.18(7) 135.94(9) 168.49(10) 175.46(9) 147.22(9) 128.91(8)

a Symmetry transformations used to generate equivalent atoms: #1, -x + 2,-y + 2, -z + 1; #2, x + 1, y, z - 1; #3, x + 1, y, z; #4, -x + 2, -y + 1, -z + 1; #5, x-1, y, z; #6, x-1, y, z + 1.

that the template may become an integral part of the structure, which may collapse on the removal of the template. This problem could be addressed by combining oxovanadium chains or layers with metal-organic coordination polymers that “pillar” the oxovanadium structures and prevent them from collapsing into densely packed solids. Fortunately, a number of reasonably oxophilic transition metals form stable organoamine compounds in reaction media that are also suitable for the generation of oxovanadium chains and layers. This offers the opportunity for developing synthetic routes for new mixed-metal inorganic-organic porous framework solids. Crystals of 1 and 2 are stable in air and insoluble in cold and hot water and common organic solvents. These materials are readily isolated in moderate to high yields in highly crystalline form from the hydrothermal reactions described earlier. These materials exhibit shiny faces and brown and golden yellow colors, respectively.

Table 3. Atomic Coordinates (× 104) and Equivalent Isotropic Displacement Parameters (Å2 × 103) for 2a Co(1) Co(2) V(1) V(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) N(1) N(2) N(3) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) O(11) O(12) O(13) O(14)

x

y

z

U(eq)

2500 5000 3552(1) 3924(1) 2997(1) 3670(1) 3876(1) 3812(1) 3666(1) 4491(1) 5269(1) 3000(1) 2610(1) 4574(1) 3082(1) 3396(1) 3639(1) 3558(1) 3243(1) 2372(1) 2325(1) 2531(1) 2794(1) 2826(1) 4331(1) 4028(1) 3969(1) 4227(2) 4514(1) 5000 5031(9) 4794(5) 4650(9)

2500 0 903(1) -891(1) 1266(2) -184(2) 2043(3) -2284(2) -306(2) -709(2) 836(3) 3878(2) 2686(2) 1509(3) 4767(3) 5659(3) 5665(3) 4739(3) 3876(3) 3482(3) 3454(3) 2549(3) 1755(3) 1848(3) 2014(3) 2941(3) 3382(3) 2866(4) 1933(4) 5190(30) 4980(20) 4192(13) 3190(20)

0 5000 606(1) 3186(1) 271(2) 1765(2) 1051(2) 3029(2) 4284(2) 3629(2) 3680(3) -20(2) 2006(2) 4941(3) 784(3) 806(3) -52(3) -875(3) -818(3) 2441(3) 3600(3) 4384(3) 3951(3) 2780(3) 3914(3) 3861(3) 4929(3) 5995(3) 5961(3) 7500 6590(30) -297(14) 1100(20)

10(1) 14(1) 12(1) 11(1) 14(1) 24(1) 29(1) 28(1) 19(1) 22(1) 35(1) 13(1) 12(1) 17(1) 17(1) 18(1) 16(1) 18(1) 18(1) 13(1) 15(1) 14(1) 21(1) 17(1) 19(1) 19(1) 17(1) 33(1) 32(1) 92(3) 92(3) 92(3) 92(3)

a U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor.

Although the colors of these compounds do not necessarily indicate the presence of reduced vanadium sites, redox titration was performed on each sample. In each case, results indicated the presence of fully oxidized (VV) centers in the compounds. The infrared spectra of compounds [Co(4,4′-bipy)V2O6] (1), and [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2) differ significantly. The four bands between 1600 and 1400 cm-1, which are attributed to the ring-stretching vibrations of the 4,4′-bipyridine,29,30 are observed in the spectra of both compounds. Additionally, the IR spectrum of [Co(4,4′-bipy)V2O6] (1) exhibits a strong, sharp band at 954 cm-1, a medium sharp band at 899 cm-1, and a strong band at 816 cm-1. The spectrum of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2) also shows additional strong and sharp bands at 961, 935, and 908 cm-1. The significant difference in the position of the absorption bands of the two compounds in the region below 1000 cm-1 is indicative of the significant structural differences in the metal oxide framework of the two compounds. Furthermore, additional bands below 800 cm-1 region due to asymmetric and symmetric (V-O-V) stretching are present in the IR spectra of both compounds. Atomic coordinates of 1-2 are given in Tables 1 and 3, respectively. Selected bond distances and angles are listed in Tables 2 and 4, respectively. A drawing of the basic building block unit of the crystal structure of 1 is (29) Topacli, A. Spectrochim. Acta 1995, 51A, 633-641. (30) Bagshaw, S. A.; Cooney, R. P. Appl. Spectrosc. 1996, 50, 310315.

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Table 4. Selected Bond Lengths [Å] and Angles [deg] for 2 Co(1)-O(1) Co(1)-N(1) Co(1)-N(2) Co(2)-O(6) Co(2)-N(3) Co(2)-O(7) V(1)-O(3) V(1)-O(1) V(1)-O(2) V(1)-O(5)#3 V(2)-O(4) V(2)-O(6) V(2)-O(2) V(2)-O(5) O(1)#1-Co(1)-O(1) O(1)-Co(1)-N(1)#1 O(1)-Co(1)-N(1) N(1)#1-Co(1)-N(1) O(1)-Co(1)-N(2)#1 O(1)-Co(1)-N(2) N(1)#1-Co(1)-N(2) N(1)-Co(1)-N(2) N(2)#1-Co(1)-N(2) O(6)-Co(2)-O(6)#2

2.020(2) 2.189(3) 2.262(2) 2.043(2) 2.139(3) 2.150(3) 1.621(3) 1.674(2) 1.784(2) 1.797(2) 1.616(3) 1.668(2) 1.796(2) 1.801(2) 180.00(9) 89.71(9) 90.29(9) 180.00(15) 88.86(9) 91.14(9) 87.42(9) 92.58(9) 180.00(13) 180.00(12)

O(6)-Co(2)-N(3) O(6)#2-Co(2)-N(3) N(3)-Co(2)-N(3)#2 O(6)-Co(2)-O(7)#2 O(6)-Co(2)-O(7) O(6)#2-Co(2)-O(7) N(3)-Co(2)-O(7) N(3)#2-Co(2)-O(7) O(7)#2-Co(2)-O(7) O(3)-V(1)-O(1) O(3)-V(1)-O(2) O(1)-V(1)-O(2) O(3)-V(1)-O(5)#3 O(1)-V(1)-O(5)#3 O(2)-V(1)-O(5)#3 O(4)-V(2)-O(6) O(4)-V(2)-O(2) O(6)-V(2)-O(2) O(4)-V(2)-O(5) O(6)-V(2)-O(5) O(2)-V(2)-O(5) V(1)-O(1)-Co(1) V(1)-O(2)-V(2) V(2)-O(6)-Co(2)

88.37(10) 91.63(10) 180.00(16) 91.19(11) 88.81(11) 91.19(11) 88.49(12) 91.51(12) 180.00(12) 111.16(14) 109.85(13) 108.55(11) 108.90(13) 108.85(11) 109.52(12) 108.79(15) 108.20(14) 111.37(13) 108.70(13) 110.95(12) 108.75(12) 150.28(14) 160.21(18) 141.08(15)

Symmetry transformations used to generate equivalent atoms: #1, -x + 1/2, -y + 1/2, -z; #2, -x + 1, -y, -z + 1; #3, x, -y, z - 1/2; #4, x, -y, z + 1/2; #5, x, -y + 1, z - 1/2; #6, -x + 1/2, -y + 1/2, -z + 1; #7, x, -y + 1, z + 1/2; #8, -x + 1, y, -z + 3/2.

Figure 2. Expanded view showing the linking of the building block units in [Co(4,4′-bipy)V2O6] (1).

Figure 1. View of the basic building block unit of the crystal structure of [Co(4,4′-bipy)V2O6] (1) showing the atom labeling scheme (hydrogen atoms are omitted for clarity). Displacement ellipsoids are drawn at the 50% probability level.

shown in Figure 1 and an expanded view showing how these units are linked is presented in Figure 2. This compound crystallizes in triclinic space group P1 h with one cobalt atom, two vanadiums, six oxygens, and one 4,4′-bipyridine in the asymmetric unit. The structure is comprised of {CoO3N2} trigonal bipyramids, linked in two dimensions by corner-sharing {VO4} tetrahedra and in the third dimension by the 4,4′-bipyridine ligands. In the bimetallic layers, the cobalt centers are bridged alternately by {VO4} and {V2O7} units, generating alternating eight-membered {Co2V2O4} and twelvemembered {Co2V4O6} rings. The trigonal bipyramidal coordination environment of the cobalt atom in 1 is defined by three oxygen donors from three {VO4} groups in the equatorial plane and two nitrogen donors from two 4,4′-bipyridine groups in the axial positions. The 4,4′-bipyridine ligands complete the three-dimensional hybrid structure by linking cobalt centers on two adjacent bimetallic layers. The overall

packing is efficient, with a cell volume per nonhydrogen atom of 15.8 Å3. A view of the crystal packing, projected approximately down the b-axis, is shown in Figure 3. Figure 4 is a view of the metal atoms and their coordination spheres in 2. There are two types of octahedral Co2+ ions linked by a {V2O7} group. Both of these cobalt atoms are situated on inequivalent crystallographic inversion centers. The first of these, Co1, is bound to four bipyridine nitrogen atoms and to two oxygens from the oxovanadium group via Co-O-V linkages. Bound to Co2 are two bipyridine nitrogen atoms, two oxygens from the bridging {V2O7}, and two water molecules. Each one of the two vanadium atoms contains one terminal oxygen atom (O3 and O4) and is linked into an infinite chain by the bridging oxygen atoms O2 and O5. The cobalt atoms in 2 are linked in three dimensions by bridging 4,4′-bipyridyl ligands as shown in Figure 5, a view of the crystal packing projected approximately down the c-axis. Also evident in this figure are the rather large channels and the [V2O7]n chains, both parallel to the c-axis. A disordered water molecule of crystallization is present in the channels. The major components of this disordered water could be modeled by four partial oxygen atoms. In accord with the elemental analysis, the sum of the occupancy factors of these partial atoms was constrained to 1.0 and their displacement parameters were constrained to be identical. The refined occupancy factors ranged from 0.16 to 0.40. The remarkable thermal stability of the hybrid framework of [Co(4,4′-bipy)V2O6] (1) is shown by the result of the TGA experiment. There is no noticeable weight loss up to 422 °C. The compound decomposes in the

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Figure 3. View of the crystal packing, projected approximately down the b-axis, in [Co(4,4′-bipy)V2O6] (1).

Figure 4. View of a building block unit in the crystal structure of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2) showing the atoms in the asymmetric unit plus the symmetry related atoms (to complete the metal coordination spheres) and 4,4′bipy ligands (hydrogen atoms are omitted). Displacement ellipsoids are drawn at the 50% probability level.

temperature range 422-445 °C. The observed total weight loss, 38.21%, in this temperature range corre-

sponds to the removal of one 4,4′-bipyridine (calculated 37.80%) per formula unit. The TGA and DTA curves resulting from the thermogravimetric analysis of 2 show that the thermal decomposition of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O is initiated by loss of water molecules in two steps. The observed weight loss (6.5%) in the 199-234 °C temperature range corresponds to the release of four water molecules per formula unit (calculated 6.84%). Furthermore, the three-step weight loss (∼44.45%) occurring at 336-447 °C corresponds to loss of three 4,4′-bipyridine per formula unit. The dehydration process of this material occurs at elevated temperature. This is not surprising because of its complex three-dimensional network structure based on substructures.31 The golden yellow color of the crystals of 2 changes to light green upon heating at 234 °C in a He stream. The color of the heated sample persists for a long time at room temperature and remains unchanged when the heated crystals are dipped in liquid hydrogen. The heated sample retains its crystallinity and structure. The BET surface area measurements of 2 show that the compound has only a modest surface area (3.5 m2/g)

Figure 5. View of the crystal packing diagram in [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2), projected approximately down the c-axis, showing the channels parallel to the c-axis. Water of crystallization present in the channels is not shown.

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Figure 6. Dependence of the magnetic susceptibility χ (0) and effective magnetic moment µeff (O) of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2) on temperature T. The line drawn through the data is the fit to the equation of zero field splitting of spin (S ) 3/2) multiplets.

Figure 7. Dependences of the magnetic susceptibility χ (0) and effective magnetic moment µeff (O) of a heated sample of [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚2H2O (2) on temperature T. The line drawn through the data is the fit to the equation of zero field splitting of spin (S ) 3/2) multiplets.

which does not change appreciably upon heating at 234 °C. This result could possibly be attributed to the method employed for surface area measurement. It has been pointed out recently that there are difficulties associated with performing BET nitrogen surface area measurement of organic-inorganic nanocomposites with fairly large organic surface groups.32 Magnetic susceptibility data for 2 are represented in Figure 6. The effective moment of the compound increases with temperature and reaches a value of 7.34 µB (5.19 µB per Co atom) at 300 K. At low temperature a rapid decrease of magnetic moment is observed which is attributed to weak antiferromagnetic interaction between cobalt(II) centers. The description of the experimental results made use of the equation for zero field splitting of spin multiplets (two S ) 3/2 cobalt (II) ions per molecule):

µeff ) x8Tχ0 at 300 K is 7.33 µB per molecule (5.18 µB per cobalt ion).

NAg2µB2 3 + 2/x + (3 - 2/x)e-2x χ ) χ0 + χTI ) 2 + χTI k BT 4(1 + e-2x) (1) where x ) D/kBT. The calculated susceptibility χ has been corrected for exchange interaction zJ′ between spins:

χ′ )

χ0 1 - (2zJ′/NAg2µB2)χ

(2)

The best fit was for g ) 2.71, D/kB ) 139 K, zJ′/kB ) -0.02 K, and χTI ) -0.0015 cm3/mol. The magnetic susceptibility curve for a heated (at 234 °C in He stream) sample of 2 (shown in Figure 7) is essentially the same as that obtained for a nonheated sample within the experimental error. The best fit was g ) 2.70, D/kB ) 137 K, zJ′/kB ) -0.02 K, χTI ) -0.0015 cm3/mol. The recalculated effective magnetic moment (31) Petit, S.; Coquerel, G. Chem. Mater. 1996, 8, 2247-2258. (32) Kruk, M.; Jaroniec, M. Chem. Mater. 2001, 13, 3169-3183. Thanks to the reviewer for bringing this point to our attention.

Concluding Remarks The synthesis of the novel hybrids 1 and 2 illustrates the potential of the synthetic approach employing vanadium oxides and organoamine metal complexes for the design and synthesis of composite porous framework solids. These materials are composed of vanadium oxide moieties and organoamine complexes. The structural types presented by these materials show that the geometric structure of the organoamines, the ligand-tocobalt ratio, and the length of spacer group between the amine nitrogen donors may have profound effects on the microstructures. This approach might be applied over a range of transition metal oxides as long as the reaction conditions are controlled to give the designed target networks and frameworks. As these hybrid networks are among the very few known mixed metal oxide hybrids involving vanadium oxide moieties, they could be used as models for further studies related to structural modifications on metal oxides and related materials. Accumulation of synthetic methods and structural data for such types of materials may lead to powerful techniques for new designer solids. Acknowledgment. This work was supported by a grant (to M.I.K.) from the American Chemical Society’s Petroleum Research Fund (ACS-PRF 35591-AC5) and NSF (CHE-0210354). C.J.O. and V.G. gratefully acknowledge the support from the Louisiana Board of Regents (contract NSF/LEQSF (2001-04)-RII-03). Supporting Information Available: X-ray crystallographic files in CIF format for the structure determinations of [{Co(4,4′-bipy)}(V2O6)] (1) and [{Co2(4,4′-bipy)3(H2O)2}V4O12]‚ 2H2O (2), and tables of crystal data for 1 and 2 (pdf). This material is available free of charge via the Internet at http://pubs.acs.org. CM049071D