Crystal structures, vibrational spectra, and normal coordinate analysis ofcis-(Et4N)[OsF2Cl4] and trans-(Ph4P)[OsF2Cl4]

By oxidation of the pure fluorochloroosmates(IV) with KBrF4 or PbO2/trifluo racetic acid in dichloromethane the mixed pentavalent complex anions cis-[O sF2Cl4](-) and trans-[OSF2Cl4](-) are formed. X-ray structure determination s on single crystals have been performed of cis-(Et4N) [OsF2Cl4] (1) (monoc linic, space group P2(1)/n, a = 7.519(2), b = 17.648(2), c = 11.942(4)Angst rom, beta = 105.98(2)degrees, Z = 4) and trans-(Ph4P)[OsF2Cl4] (2) (tetrago nal, space group P4/n, a = 12.677(2), c = 7.743(1) Angstrom Z = 2). Based o n the molecular parameters of the X-ray determinations and assuming C-2v po int symmetry for the anion of 1 and D-4h point symmetry for the anion of 2 the IR and Raman spectra have been assigned by normal coordinate analysis. Due to the stronger trans influence of chlorine as compared with fluorine f or F-.-Os-Cl' axes significally different valence force constants are obser ved in comparison with symmetrically coordinated axes: fd(OsF.) = 3.35, f(d )(OsF) = 3.73, f(d)(OsCl') = 2.05 and f(d)(OsCl) with 1.98 and 2.00 mdyn/An gstrom.