Polyoxometalates with supporting phosphate ligand: synthesis and characterization of (alpha)-[SiW11O39M(H2PO4)]n-

A novel series of Keggin species with a covalently bonding support-ligand, formulated (alpha)-[SiW11O39M(H2PO4)]n-(M = CoII, MnII, NiII or CrIII), have been synthesized and characterized by elemental analyses, IR, CV, NMR and X-ray powder diffraction measurements. The structure is reminiscent of an ancient Chinese three-legged wine vessel, and is a possible model for POMnucleotide interaction. An interesting property is the different thermal behaviors for this series in comparison with those for corresponding 3d metal monosubstituted Keggin polyoxometalates. This can be attributed largely to the pendant surface ligand and H bonding interaction. Compared with (alpha)-PW11M, the orders of line broadening of 31P NMR signals are the same for the two series of complexes (alpha)-PW11M and (alpha)-SiW11M-PO4, but both contact and dipolar interactions might make a significant contribution to the chemical shift for phosphorus for the latter.