Nonstoichiometric channel chalcogenides Tl xV 6S 8: topotactic redox reactions and NMR studies

Abstract

The thallium atoms in the lattice channels of the metallic conducting system Tl x V 6S 8 are shown to be mobile at ambient temperature. As indicated from galvanostatic charge transfer, X-ray and 51V NMR data, the Tl content is variable within 0.78⩾ x⩾0.17 by means of reversible topotactic redox reactions. 205Tl NMR spectra reveal that below x = 0.5 the bonding state of the Tl atoms is rather ionic, as expected from the simple charge transfer intercalation model. In contrast, at higher contents partial metallic bonding is observed, indicating the Tl atoms to retain some electron density from the matrix conduction band by delocalized multicenter bonding within quasimolecular one-dimensional clusters inside the V 6S 8 matrix.