MULTICOMPONENT POLYANIONS - 53 - STRUCTURE OF TETRAKIS(TRIMETHYLAMMONIUM) UAHEXADECAOXO(TRIOXOPHENYLPHOSPHATO)HEXAMOLYBDATE) DIHYDRATE, [NH(CH3)(3)](4)[((C6H5P)MO6O21(H2O)(3))(2)].2H(2)O

The title compound crystallized in the monoclinic space group P2(1)/n (No. 14) [a = 11.211 (5), b = 12.862 (3), c = 23.05 (1) Angstrom, beta = 94.37 (3)degrees, V = 3314 (2) Angstrom(3), Z = 2]. The polyanion c an be regarded as a dimer of a phenylphosphonatohexamolybdate, (C6H5P) Mo6O23(H2O)(3), Linked by four O atoms. In this monomeric unit the six molybdenum octahedra are grouped into two parts consisting of four an d two edge-sharing octahedra, respectively. These two parts are connec ted by two corner-sharing O atoms to form a bent Mo-6 ring. The phenyl phosphonate group coordinates to the Mo-6 ring from the narrow side as a tripodal Ligand. The {(C6H5P)Mo6O21 (H2O)(3)}(2) units form layers parallel to (001) and the structure is stabilized by hydrogen bonds be tween water and neighboring anions. The monomeric unit has been shown to be a key structure in the process of deducing the aqueous solution structures of the (C6H5P)Mo-6(2-) and (C6H5P)Mo-7(4-) species found in a previous equilibrium study of the H+-MoO42-(C6H5P)O-3(2-) system.