Syntheses, Structures And Performances Of Metal-oxo Clusters-Hybrid Materials

Recently, polyoxometalates (POMs) have become an important embranchment in the field of chemical research, owing to their diverse structures and potential applications in many fields such as catalysis, adsorption and medicine. Currently, the research of POMs has reached the extremely significant level. A series of hybrid materials with novel structures have been synthesized, mainly using organic groups or metal coordination complexes to interact with the oxygen atoms of POMs.During our research of POMs, we synthesized a series of heteropoly-phosphomolybates, heteropolyoxotungstates and polyoxovanadates. Moreover, we have synthesized some cobalt and nickel coordination polymers with N-containing ligands. All have been characterized by elements analyses, IR, and X-ray single crystal structural analyses. The thermal analyses, XPS, magnetic properties and fluorescence properties of some compounds have also been studied. Our work will develop and investigate the reactivity of reactants and mechanism of synthesis under hydrothermal conditions, which provide the basics for rational synthesis of clusters with particular characteristics.1. PolyoxomolybatesWe obtained ten phosphomolybate, which are based on [P₄Mo₆] structural units (1-7), [PMo₁₂O₄0] units (8 and 9) and [P₂Mo₅] units (10) under hydrothermal conditions. (H₃dien)₃{[Cd(Hdien)(H₂O)]2·Cd[(PO₄)₄(MoO₂)6(OH)₃]₂}·H₃O·7H₂O (1), {[(H₂dien) Cd(H₂O)]₂Cd[(H₂PO₄)(HPO₄)2(PO₄)(MoO₂)6(OH)₃]}·dien·6H₂O (2), [Co(dien)₂](H₃dien)₆{[CoMo₁₂O₂4(OH)6(HPO₄)₂(PO₄)₆][Co(Hdien)]₂[CoMo₁₂ O₂4(OH)₆(PO₄)₈]}(dien)·4H3O·5H₂O (3), (H₃dien)₂{Na[(HPO₄)2(PO₄)₂(MoO₂)₆ (OH)3]}·4H₂O (4), (H₃dien)₄[NiMo12O₂4(OH)6(HPO₄)4(PO₄)4]·10H₂O (5), (H3dien)4[CoMo12O₂4(OH)6(HPO₄)4(PO₄)4]·10H₂O (6), (H3dien)4[CdMo12O₂4 (OH)6(HPO₄)4(PO₄)4]·8H₂O (7), [4,4′–H₂bipy]2[PMoVI9MoV3O₄0]·2H3O (8), [4,4′–H₂bipy]2[PMoVI11MoVO₄0]·2H₂O (9) and (H3dien)2[P2Mo5O₂3] (10). In compounds 1-7, [P4Mo6] cluster units are firstly connected by transition metal or alkali metal producing [M(P4Mo6)2] subunit which are further linked by transition metal complexes, metal-oxygen polyhedra or hydrogen bonds to result in extended structures. Compound 1 is a 2-D sheet which forms from coordination complexes [Cd(Hdien)(H₂O)]3+ linking [M(P4Mo6)2] subunits. Compound 2 possesses 1-D chain structure constructed from two coordination complexes [Cd(H₂dien)(H₂O)]4+ as bridges linking subunits [Cd(P4Mo6)2]. Compound 3 is the first example of 1-D castle-like compound forming from coordination complexes [Co(Hdien)]3+ linking subunits [Co(P4Mo6)2] which are arranged both standing and lying modes. Compound 4 is a 1-D chain which is constructed from [M(P4Mo6)2] subunits linked through alkali metals. Compounds 5-7 contain discrete clusters. These three compounds all exhibit 3-D supramolecular structures through hydrogen bonding interactions among cluster anions, water clusters and organic ligands. In compounds 8-10, cluster anions [PMo12O40] or [P2Mo5] are connected into 3-D supramolecular network by N-H···O hydrogen bonds. The fluorescence properties of compounds 1, 3-7 were measured. All of these compounds show fluorescence activities assigned to LMCT. The magnetic behaviors of compounds 3 and 6 were measured which exhibit anti-ferromagnetic interactions.2. PolyoxotungstatesSeven heteropolyoxotungstate based on Keggin or pseudo-Keggin structures have been synthesized, these are [Ni(2,2′–bipy)3]1.5[AsWVI10WV2O40Ni (2,2′–bipy) 2(H2O)]·0.5H2O (11), [Ni(H2O)4(4,4′–bipy)2]2[AsWVI11WVO40] (4,4'–bipy)4·8H2O (12), [Ag(2,2′–bipy)2]8[(AsWVI10WV2O40)Ag(2,2′–bipy)]2 (13), [Ni(H2O)2 (4,4'–Hbipy)2(4,4'–bipy)][SiW12O40] (14), [Co(en)3]2(SiW12O40)·H2O (15), (4,4'–H2bipy)2(SiW12O40)·2H2O (16) and [Ni(enMe)2][Ni(enMe)2(H2O)2]2 [PWVI9WV3O40]·H2O (17). 11 and 13 contain discreteα-Keggin tungstoarsenate anion supported transition metal complex [Ni(2,2′–bipy)2(H2O)]2+ and[Ag(2,2′–bipy)]+ respectively. These tungstoarsenate supported complexes are rarely reported. In compound 11, cluster anions [AsWVI10WV2O40Ni(2,2′–bipy)2 (H2O)]are connected into 3-D supramolecular network by hydrogen bonds. In 13, cations [Ag(2,2'–bipy)2]+ are filled in 3-D supramolecular tunnel constructed from cluster anions. The cluster of compound 12 is pseudo-Keggin tungstoarsenate, in 12, cluster anions and template agents form inter-lock chains through hydrogen bonds, heptanuclear and octanuclear water clusters are connected by transition metals into 1-D water chains. Compounds 14, 15 and 16 are all tungstosilicates. Compound 14 is 2-D supramolecular structure which consists of cluster anions [SiW12O40]4- and 1-D covalent chain [Ni(H2O)2(4,4'–Hbipy)2(4,4'–bipy)]n4n+. In compounds 15 and 16, cluster anions are connected into 3-D supramolecular network by hydrogen bonds. Compound 17 is tungstophosphate consisting of a 2-D sinusoidal sheet which forms from hydrogen bonding interactions among 1-D covalent chains [Ni(enMe)2(H2O)2]2[PWVI9WV3O40]n2n-. The magnetic behaviors of compound 11 were measured which exhibits anti-ferromagnetic interactions. 3. PolyoxovanadatesThree polyoxovanadate compounds [V10O26(OH)2]·2(HMTA)·4H3O·4H2O (18); [Ni(enMe)3]2[VIV6VV9O36Cl]·2H2O (19) and [Co(en)3]2[VIV6VV9O36Cl]·2H2O (20) have been synthesized. In the three compounds, hydrogen bonding interactions play important roles in the formation process of the high-dimensional supramolecular network. Compound 18 was obtained from water solution. In 18, crystallization water molecules self-assemble into octanuclear water cluster, [V10O28]6- anions serve as guest molecule filling in tunnels which is composed of water clusters and HMTA. Compounds 19 and 20 are isostructural, the cavities in 2-D supramolecular structure constructed from crystal waters and [V15O36]12- anions are filled by [Ni(enMe)3]2+ and [Co(en)3]2+ cations as guest molecules respectively.4. Nickel and cobalt coordination polymer with nitrogen-containing ligandsSix nickel and cobalt coordination polymers with nitrogen-containing ligands Co(N2H5)2(μ2–SO4)2 (21); {[Ni(4,4'–bipy)2(H2O)4](C6H6NSO3)2·2H2O}n (22); [Ni(C20H12N2O4)2(H2O)2]·2C3H7NO (23); [Co(2–NH2py)2(ox)] (24); [Ni(2–NH2py)2 (ox)] (25) and {[Ni(Pht)(4,4'–bipy)(H2O)2]·2H2O}n (26) have been synthesized. The hydrothermal hydrolysis of sulfanilic acid gives birth to sulfate 21. It is a 1-D chain consisting of four-number ring which is formed from corner-sharing SO42- tetrahedra and [CoN2O4]2+ octahedra. Compound 22 is 3-D supramolecular structure which is constructed from supramolecular chain (C6H6NO3S)nn- and covalence chain [Ni(C10H8N2)2(H2O)4]n2n+. 23 contains mononuclear coordination unit, which is linked by O–H···O hydrogen bonds to form 3-D supramolecular network. The isomorphic compounds 24 and 25 are composed of one-dimensional zigzag chains built up via the [M(2-NH2py)2]2+ fragments bridged by tetradentate oxalate ligands.. Compound 26 is 2-D sheet with square lattice which is constructed from ortho-phthalic acid and 4,4'–bipy. Compound 26 displays fluorescence activity. The magnetic behaviors of compounds 21 and 24 were measured which exhibit anti-ferromagnetic interactions.