By careful oxidation of the pure fluorochloroosmates(IV) with BrF3 in dichloromethane the mixed pentavalent complex anions [OsF5C1]_ and m -[O sF 4Cl2] _ are formed. X-ray structure determinations on single crystals have been performed of (Ph3PNPPh3)[OsF5C l]C H 2Cl2 (1) (triclinic, space group P i, a = 12.153(5), b = 12.387(5), c = 14.229(5) A , a = 70.07(1), ß = 65.46(1), 7 = 72.87(1)°, Z = 2) and ds-(P h 3PNPPh3)[OsF4Cl2] C H 2Cl2 (2) (triclinic, space group P i, a = 11.987(2) b = 13.083(2), c = 14.456(2) A , a = 66.30(1), ß = 65.47(1), 7 = 71.22(1)°, Z = 2). Based on the molecular parameters of the X-ray determinations the IR and Raman spectra for the anions of 1 and 2 have been assigned by normal coordinate analysis. Due to the mutual trans influences the valence force constants of asymmetrically coordinated octahedral axes F*-Os-Cl' differ from those of the symmetric F-Os-F axes. The data are for 1: fd(OsF*) = 3.95, fd(OsF) = 4.07, fd(OsCl') = 2.51 and for 2: fd(OsF*) = 3.45, fd(OsF) = 3.97, fd(OsCl') = 2.42 mdyn/A.