Acta Crystallographica Section B

Structural Science

Volume 54, Part 4 (August 1998)

research papers

Acta Cryst. (1998). B54, 424-430 [ doi:10.1107/S010876819701776X ]

Multicomponent Polyanions. 53. Structure of Tetrakis(trimethylammonium) Tetra--oxo-bis(triaquahexadecaoxo(trioxophenylphosphato)hexamolybdate) Dihydrate, [NH(CH₃)₃]₄[{(C₆H₅P)Mo₆O₂₁(H₂O)₃}₂\].2H₂O

D.-G. Lyxell, D. Boström, M. Hashimoto and L. Pettersson

Abstract: The title compound crystallized in the monoclinic space group P2₁/n (No. 14) [a = 11.211 (5), b = 12.862 (3), c = 23.05 (1) Å, [beta] = 94.37 (3)°, V = 3314 (2) Å³, Z = 2]. The polyanion can 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 and two edge-sharing octahedra, respectively. These two parts are connected by two corner-sharing O atoms to form a bent Mo₆ ring. The phenylphosphonate group coordinates to the Mo₆ 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 between 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⁺-MoO $_4^{2-}$ -(C₆H₅P)O $_3^{2-}$ system.