Multicomponent polyanions. 57. Large-angle X-ray scattering study of aqueous molybdophenylphosphonate solutions

The radial distribution functions are calculated from large-angle X-ray sca ttering (LAXS) measurements for one concentrated aqueous molybdate/heptamol ybdate solution and fi ve aqueous molybdophenylphosphonate solutions (lithi um chloride medium). Besides water and hydrated lithium, chloride, and moly bdate ions, five species in all, having different nuclearities, are postula ted to exist in the solutions, according to equilibrium studies using poten tiometry and P-31 NMR spectroscopy. The structures of the three polymolybda te species Mo7O246-, Mo8O264-, and (C6H5P)(2)Mo5O214-, for which the struct ures are determined crystallographically. are confirmed to exist also in aq ueous solution. The principal structures of the remaining two complexes, (C 6H5P)Mo6O21(OH2)(5)(2-) and (C6H5P)Mo7O25(OH2)(4-), are elucidated with the use of structures of related species. Bath anions have one group of four e dge-sharing MoO6 octahedra and another group of two MoO6 octahedra connecte d by sharing corners, forming a bent unsymmetric six-membered ring, with th e C6H5PO3 group placed on the crowded side of the ring. In the former,, the group of two MoO6 octahedra is edge-shared, while in the latter, the group is face-shared, resulting in a ring small enough to tetrahedrally coordina te to the seventh molybdenum opposite the phenyl group.