A structural study of D-mannitolatodimolybdate(VI) complexes in aqueous solution

The structure of the D-mannitolatodimolybdate(VI) complex has been determined by means of large angle X-ray scattering (LAXS) in aqueous solution at two pH values, 2.0 and 5.5. The two complexes have in principle the same structure in aqueous solution, two face-sharing molybdate(VI) octahedra connected to one D-mannitol ligand, as previously observed in the solid state. In the deprotonated form of the complex, pH 5.5, the D-mannitol ligand has lost a proton and as a result the MoMo distance is 0.054 Å shorter than the protonated form, pH 2.0. This indicates that it is a proton on an oxygen shared by molybdate groups that leaves the complex at deprotonation and forces the molydate(VI) octahedra even closer to each other.