A new method for the synthesis of organic–polyoxometallate hybrid compounds

The reaction of the Na2MoO4 or Na2WO4 salt with organic amine and PCl5, SiCl4 or TiCl4 in hydrochloric acid medium under hydrothermal conditions yields organic–polyoxometallate hybrid compounds, with the following reaction formula: Na2MO4 + Lewis-base + XCln + HCl → (Lewis-baseH)m(XM12O40) + NaCl + H2O (M = Mo or W; X = P, Si, Ti,; n = 3–5). By using this method, four new complexes, [(CH3)2NH]3[H3PW12O40] (1), (C2H5OH)3(H3PMo12O40) (2), [DMDA]2[H4SiW12O40]·H2O (3) (DMDA = 1 N,3 N-dimethyl-1,3-diazolidine) and [(DAN)6][H4TiW12O40]·4H2O (DAN = 4,4′-dianiline) (4), were obtained, and their crystal structures are reported. Thermal analysis of 1, 2 and 4 has been carried out. The thermal analysis indicates that the Keggin anion skeleton begins to decompose at about 300 °C. The possibility of constructing hydrogen-bond interactions by association between the polyoxometallate and the organic compound is explored. The roles of solvents and organic groups in the formation of specific crystalline architectures are discussed. The crystal structure of [H4TiW12O40], a hetero-transition-metal Keggin polyoxometallate with a square-plane TiO4, has been reported. Four architectures developed by hydrogen-bond associations of different Keggin polyoxometallates and organic bearing N–H or O–H donor functions are described. The selected organic modules (4,4′-dianiline, 1,3-dimethylimidazolidine, dimethylamine and ethanol) possess hydrogen-donor functions to allow them to act as bridges between polyoxometallate groups. Depending on the nature of the donor group, the number of hydrogens available for bonding, the geometric features and the sizes of the organic modules, diverse assembling patterns have been observed ranging from one-dimensional to three-dimensional networks. For all the networks, H3O+ and H+ act as actual linkers between the molecular units.

Graphical abstractA simple method is reported for the synthesis of four organic-polyoxometallate hybrid compounds. The first crystal structure of a hetero-transition-metal Keggin polyoxometallate, [H4TiW12O40], with a square-planar TiO4 unit is described in this paper. This methodology will hopefully make it possible to synthesise hetero-transition-metal Keggin compounds.Synthetic method for the preparation of organic–polyoxometallate hybrid compounds: Na2MO4+Lewis-base+XCln+HCl→(Lewis-base)mPOM+NaCl+H2ONa2MO4+Lewis-base+XCln+HCl→(Lewis-base)mPOM+NaCl+H2OM = Mo or W. X = P, Si, or Ti. n = 4 or 5.Figure optionsDownload full-size imageDownload as PowerPoint slide