Crystal structures of two new heptamolybdates and of a pyrazole incorporating a gamma-octamolybdate anion

Two new heptamolybdates, one containing calcium and imidazole and the other with urea and ammonium cations, have been prepared. X-ray crystallographic studies of single crystals of both compounds have been carried out. In the mixture of calcium and imidazole [(Himi)(4)][Ca(H2O)(6)(mu-O)(2)][Mo7O24]. 2(imi). 3H(2)O (1), the calcium(II) cation is surrounded by six water mole cules and two oxygen atoms from the polyanion, and bridges in trans positio n two [Mo7O24](6-) polyanions forming a linear composite with alternating M o7O24 and Ca(H2O)(6) units. The urea compound [CO(NH2)H](3)(NH4)(9)[Mo7O24] (2). 5[CO(NH2)(2)]. 4H(2)O (2) presents [Mo7O24](6-) heptamolybdate anions bound by hydrogen bonds from NH4+, [CO(NH2)H] cations and H2O molecules. A new crystalline phase of a gamma-octamolybdate containing pyrazole coordina tively bound to molybdenum has also been prepared [(Hpyr)(4)][(pyr)(2)(Mo8O 26)]CH3COCH3. 2H(2)O (3). The structure has been solved by X-ray diffractio n from a single crystal. The Mo-N bond length is 2.262(3) Angstrom. All com pounds have been characterised by IR,H-1 NMR and thermal analysis. (C) 1999 Elsevier Science S.A. All rights reserved.