Intermetallic charge transfer in MTiF6·6H2O (M = Mn, Fe, Co, and Ni): A study by X-ray photoelectron spectroscopy

Abstract

The X-ray photoelectron spectra (XPS) of a series of hydrated fluoridotitanates MTiF6∙6H2O (M = Mg, Mn, Fe, Co, Ni) were measured for the first time. The compounds were grown in the form of high-quality single crystals and belong to the extensive ABF6∙6H2O family. Under the action of the XPS experimental conditions (vacuum and X-ray), the process of charge transfer from divalent transition metal to the titanium atom develops, which is described as intermetallic (intervalence) charge transfer (IMCT, IVCT): M2+ + Ti4+ → M3+ + Ti3+. Dehydration and hydrolysis of the studied complexes promote the process of charge transfer through the association of isolated octahedra by an edge or a vertex. The obtained XPS data were compared with those available in the literature, which are rather ambiguous for cobalt compounds. In our case, the binding energy of Co 2p electrons is higher for Co3+ than for Co2+ in an octahedral environment.