Anderson-type ammonium hexamolybdotungstonickelates

Abstract

[Ni^IIMo_6–x^VIW_x^VIO₂₄H₆](NH₄)₄·5H₂O (x= 0,2,3,4,6), Anderson-type heteropolymetallates, have been prepared and characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), magnetic susceptibility, thermal analysis and X-ray photoelectron spectroscopy (XPS). The XRD analysis has shown that all samples are single species and consist of isomorphous solid solutions. From the determination of the unit-cell parameters it has been inferred that the monoclinic lattice volume shrinks, and that the lattice becomes more distorted with increasing tungsten content. Both DRS and magnetic susceptibility measurements have shown the presence of Ni^II in all samples. The XPS spectra have revealed that Ni^II, Mo^VI and W^VI species are also present at the surface of the materials. A higher ligand–metal charge-transfer energy with increasing W content is found by DRS and confirmed by XPS.