Infrared spectra and configurations of some molybdenum(VI) dihalide dioxide complexes

Abstract

The i.r. spectra of MoO₂X₂L₂ and MoO₂X₂L′ complexes (X = Cl or Br; L = dmf, Dmso, or pyo; L′= bipy or phen) have been compared in order to identify stretching and bending modes involving the molybdenum atom. For MoO₂Cl₂·2dmf, assignment of bands has been assisted by calculation of vibration frequencies through normal-co-ordinate analysis. The spectra of all the adducts are consistent with a cis–trans–cis-octahedral arrangement of the terminal oxygen atoms (O_t), halogens, and ligand oxygen atoms (O₁), respectively, about the molybdenum. The more weakly bonded O₁ atoms are thus co-ordinated trans to the strongly bonded O_t. There is a fairly regular relation between ligand donicity and the ν(Mo–O_t) frequency.