Crystal structure, morphology and chemical reactivity of Tl xV 5S 8

Abstract

Single crystal X-ray work reveals that with decreasing Tl content the anisotropic displacement parameter (ADP) U 22 increases indicating modified interatomic interactions of the Tl atoms, an enhanced mobility or static disorder. Furthermore, it is demonstrated that with decreasing temperature the one-dimensional disorder of the Tl atoms increases. Time dependent topotactic removal of Tl using molecular iodine in donor solvents proceeds in two steps: a relatively fast step is followed by a slow diffusion controlled reaction. About 20% of the Tl is removed within the first 60 min. After about 13 d the composition Tl 0.3V 5S 8 was reached. Further reaction results in the formation of a mixture of Tl 0.3V 5S 8 and V 5S 8. The reaction product between I 2 and Tl was identified as TlI 3 which demonstrates that Tl in Tl x V 5S 8 is in a formal oxidation state clearly below +1. The host material V 5S 8 is not attacked by I 2 as could be demonstrated by SEM. These observations imply that the vanadium sulfide is not directly involved in the redox reaction. With decreasing Tl abundance the internal mechanical stress due to anisotropic changes of the lattice parameters is increased resulting in an increased brittleness of the crystals. X-ray powder diffractometry was found to be a useful analytical tool to quantitatively determine the Tl content without destroying the sample.