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 K-2[OsBr6] with DMSO in the presence of SnBr2 at 100A degrees C and cis,fac-[OsBr2(dmso-S)(3)(dmso-O)] (2) was prepared by thermal isomerization of 1 in a DMSO solution at 150A degrees C. The coordination mode of DMSO molecules was determined by IR and H-1 and C-13 NMR spectroscopy. X-ray diffraction analysis showed that compound 2 crystallizes in the monoclinic system, space group P2(1)/n; a = 8.4711(5) , b = 27.7876(15) , c = 8.5569(5) , beta = 115.7110(10)A degrees; 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 H-1 and C-13 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-d(6))(4)], where X = Cl, Br, were isolated from DMSO-d (6) and characterized by the IR spectra.