Synthesis, structure and properties of the cluster anions [(Mo 6Cl 8i)X 6a] 2− with X aF, Cl, Br, I

Abstract

The tetrabutylammonium (TBA) salts of the octa- μ 3-chloro-hexahalogeno-octahedrohexamolybdate(2−) ions [(Mo 6Cl 8 1)X 6 a;] 2− with X aF, Cl, Br, I were synthesized from the appropriate free acid of the type H 2[(Mo 6Cl 8 1)X 6 a] with X a(BF 4) −, Cl −, Br −, I − and the corresponding TBA halide. The crystal structures determined from single crystals show systematic changes in bond distances and angles with the F a a ̊ I a ligand exchange (increasing Mo 6 octahedron; slight compression of the Cl 8 1 cube). Infrared and Raman spectra were measured in solution and in the solid state (80 K). The vibrational modes of the cluster kernel Mo 6Cl 8 1 are approximately site constant, but all vibrations with contributions of the X a ligands show characteristic shifts. The most important bands are assigned by use of normal coordinate analyses.