CRYSTAL-STRUCTURE, VIBRATIONAL-SPECTRA, A ND NORMAL-COORDINATE ANALYSIS OF TRANS-(TEA)(2)[OSI4(CO)(2)]

The X-ray structure determination of trans(TEA)(2)[Os(CO)(2)I-4] (mono clinic, space group P2(1)/n, a= 10.609(2), b = 10.659(3), c = 13.229(6 ) Angstrom, beta = 90.46(3)degrees, Z = 2) revealed the rough D-4h poi nt symmetry of the complex anion trans-[Os(CO)(2)I-4](2-) (Os-I = 2.72 6(1), 2.727(1); Os-C = 1.91(2); C-O = 1.14(2) Angstrom). Using the mol ecular parameters the IR and Raman spectra are assigned by normal coor dinate analysis. The valence force constants are fd(CO)= 15.86, f(d)(O sC) = 3.28, f(d)(OsI)=1.13 mdyn/Angstrom. The strengthening of the Os- C bond by stronger back donation of the Os-II(d(6)) complex in compari son with the isostructural Os-III(d(5)) compound is discussed.