Electron spin resonance in some molybdenum(V) halogeno-complexes

Abstract

Three paramagnetic species are shown to exist in hydrobromic acid solutions of molybdenum(V). At hydrogen bromide concentrations greater than 5·75M two of these are detectable by electron spin resonance (e.s.r.) and are believed to be monomeric. All the molybdenum present in 9·4M-hydrogen bromide is in the form of these two species, and there is evidence that the dominant species at this concentration is [MoOBr₅]^2–. The third species, whose maximum concentration is in about 6M-hydrogen bromide, may be dimeric; its presence is inferred by a comparison between e.s.r. and magnetic susceptibility data. E.s.r. in some undiluted solids of the type M₂MoOX₅(M = NH₄, K, Rb, Cs, Me₃NH, pyridinium, α-picolinium, γ-picolinium, piperidinium, anilinium, quinolinium, or quinaldinium; X = Cl or Br) and in Et₄NMoCl₆ is also reported. Evidence for weak exchange interaction between neighbouring anions is found for some of these salts.