Structure and bonding in the high molecular weight isopolymolybdate ion, [Mo36O112 (H2O)16]8-. The crystal structure of Na8[Mo36O112 (H2O)16]. 58 H2O

The crystal structure of Na8[Mo36O112(H2O)16]·58H2O which was prepared from acidified solutions has been determined from low-temperature single-crystal X-ray diffraction data. The crystals are monoclinic. The centrosymmetric [Mo36O112(H2O)16]8- ion with approximate 2/m symmetry is the largest molecular isopolymolybdate species known to date. The anion structure combines features typical for isopolymolybdates obtained from less acidic solutions as well as those of the polymeric species precipitated from strongly acidified solutions. Other features unusual for isopolymolybdates are four pentagonal bipyramidal MoO7 polyhedra and four of the 16 H2O ligand molecules bridging two Mo atoms. The rest of the H2O molecules are mostly coordinated to Na+ and form an extensive hydrogen bridge system. From the bond lengths the charge distribution over the oxygen atoms was calculated on the basis of the bond valence model