Osmium dimethyl sulfoxide complexes: Synthesis and properties of [H(dmso)2][OsIII(dmso)2Br4]

The reaction of H 2 [OsBr 6 ] with DMSO in ethanol solution resulted in DMSO complex [H(dmso-O) 2 ][Os III (dmso-S) 2 Br 4 ] ( 1 ) described previously as an intermediate product in the reaction of K 2 [OsBr 6 ] with DMSO and characterized by EAS and ESR spectra. The coordination of DMSO molecules was established by IR and 1 H and 13 C NMR spectroscopy. The oxidation state of osmium and trans arrangement of DMSO molecules in the anion were established by ESR. The behavior of complex 1 in solutions was studied by EAS, ESR, and mass-spectrometry: a displacement of Br − ions accompanied by the reduction of osmium to oxidation state +2 occurs in DMSO, a solvation with displacement of DMSO molecules is observed at the first stage in water and methanol (rate constants 2.3 × 10 −4 and 1.7 × 10 −3 s −1 , respectively), the sequential substitution of DMSO molecules and osmium oxidation to form [Os IV Br 6 ] 2− ions takes place in 4 mol/L HBr.