Crystal structure of potassium sodium hepta-hydrogen hexa-molybdocobaltate(III) octa-hydrate: an extra-protonated B-series Anderson-type heteropolyoxidometalate.

Abstract

The title compound, KNa[Co(III)(OH)7{Mo6O17}]·8H2O, was obtained by the ion-exchange technique from K3[Co(μ3-OH)6Mo6O18]·7H2O. Six μ3-O atoms and one O atom of the bridging μ2-O atom are protonated. This novel polyanion protonated by an extra H atom is an unexpected polyanion species among the B-series Anderson-type polyoxidometalates (POMs), [X(n) (+)(μ3-OH)6Mo6O18]((6-n)-)] (X = heteroatom). The extra H atom (seventh H atom) in the polyanion does not lie on a crystallographic centre of symmetry, but is located at the mid-point between two μ2-O atoms of adjacent polyanions, and forms a very short hydrogen bond [2.430 (5) Å]. The present structure is considered as particularly significant in understanding noncentrosymmetric strong hydrogen bonding.