Binuclear and heterobinuclear fluorooxo complexes of vanadium and molybdenum with the Cs 3Fe 2F 9 structure

Abstract

Cs 3Mo 2O 6F 3, Cs 3V 2O 4F 5 and Cs 3V 2O 2F 7 crystallize in the hexagonal Cs 3Fe 2F 9 structure. The structure can be described in terms of close packed Cs(O,F) 3 layers, where the octahedral sites in two adjacent layers are filled with the transition metal ions, so forming face shared bioctahedral M 2(O,F) 9 units. Single crystal X-ray data are unable to distinguish between fluorine and oxygen atoms. Therefore no information can be obtained, whether oxygen or fluorine atoms occupy terminal or bridging positions in the M 2(O,F) 9 units. Infrared and Raman spectra of these compounds, however, prove that oxygen and fluorine atoms are randomly distributed over all layers in Cs 3Mo 2O 6F 3 and in Cs 3V 2O 4F 5 leading to the predominant species [O 2FMoO 2FMo 2F] 3− and, by a random distribution of the vanadium atoms as well, to the fluorine bridged anion [O 2FVF 3VO 2F] 3−. Cs 3V 2O 2F 7 contains the anion [OF 2VF 3VF 2O] 3− with a statistical distribution of the oxygen atoms over the terminal sites. The compounds Cs 3Mo xV 2−xO x+4F 5−x and Cs 3Mo xV 2−xO 2+2xF 7−2x containing hetero binuclear anions have also been prepared. In both substances the oxygen atoms occupy terminal and bridging positions.