Gemischte Thio/Oxo-Orthovanadate Na3[VSxO4 –x] (x = 2, 3): Darstellung – Strukturen – Eigenschaften / Mixed Thio/Oxo Orthovanadates Na3[VSxO4−x] (x = 2, 3): Synthesis – Crystal Structures – Properties

Abstract

Mixed sodium thio/oxo orthovanadates(V), dark red Na3[VS3O] and orange red Na3[VS2O2], were synthesized via reactions in the melt starting from V, Na, Na2S, Na2O and sulfur. The structure of the low temperature phase of Na3[VS3O] (space group Pnma, a = 589.5(3), b = 962.8(5), c = 1186.6(6) pm, Z = 4, R1 = 0.0494) contains anions [VS3O]3− almost identical to those known from the high temperature form, β -Na3[VS3O] (space group Cmc21, a = 968.4(4), b = 1194.6(4), c = 590.5(2) pm, Z = 4, R1 = 0.0291). The second order phase transition between these two forms at 536 °C was studied by temperature dependent powder diffraction and explained on the basis of a comparison of the anion packing in the two related structures. The packing of the dithiodioxovanadate anions in Na3[VS2O2] (space group Pbca, a = 1162.7(2), b = 592.71(12), c =1766.7(4) pm, Z = 8, R1 = 0.0312) is also closely related. The chemical bonding in the anions [VS3O]3− and [VS2O2]3− of approximately ideal C3v and C2v symmetry is discussed on the basis of FP-LAPW band structure calculations and force constants obtained from Raman spectroscopy. The decrease of the calculated band gaps with increasing S content x in Na3[VSxO4−x] is in accordance with the optical properties showing a gradually deepening of the crystal and solution colour. Discernible trends in the chemical bonding in this series of mixed thio-oxo anions also include the amount of π bonding of the V-O and V-S bonds and the corresponding variation of force constants and V-O/V-S distances.