Bromo dimethyl sulfoxide osmium(II) complexes. Molecular structure of cis,fac-[OsBr2(dmso-S)3(dmso-O)]

Bromo dimethyl sulfoxide osmium(II) complexes were synthesized: trans-OsBr₂(dmso-S)₄] (1) was obtained by the reaction of K₂OsBr₆] with DMSO in the presence of SnBr₂ at 100°C and cis,fac-OsBr₂(dmso-S)₃(dmso-O)] (2) was prepared by thermal isomerization of 1 in a DMSO solution at 150°C. The coordination mode of DMSO molecules was determined by IR and ¹H and ¹³C NMR spectroscopy. X-ray diffraction analysis showed that compound 2 crystallizes in the monoclinic system, space group P2₁/n; a = 8.4711(5) Å, b = 27.7876(15) Å, c = 8.5569(5) Å, β = 115.7110(10)°; Z = 4. The coordination polyhedron of osmium is a distorted octahedron; the osmium environment is formed by two cis-arranged bromine atoms and three fac-S-coordinated and one O-coordinated DMSO molecules. The interconversion of complexes in solutions was studied by UV/Vis and ¹H and ¹³C NMR spectroscopy. In chloroform and DMSO, complex 2 isomerizes to cis-OsBr₂(dmso-S)₄] and (in the light) to 1. The complexes trans-OsX₂(dmso-d₆)₄], where X = Cl, Br, were isolated from DMSO-d ₆ and characterized by the IR spectra.