| Abstract: | Preparation and Spectroscopic Characterization of the Pure Bondisomers [OsCl5(NCS)]2? and [OsCl5(SCN)]2? The oxidation of [OsCl5I]2? with (SCN)2 in CH2Cl2 yields the bondisomers [OsCl5(NCS)]2? and [OsCl5(SCN)]2?, which are isolated as pure compounds by ion exchange chromatography on DEAE-Cellulose. Only the salts of the N-isomer show significant shifts in the vibrational and electronic spectra caused by polarization of the terminal S depending on the size of the cations and the polarity of the solvents. In the IR and Raman spectra νCN(S), νCS(N) and δNCS are found at higher wave numbers than νCN(N), νCS(S) and δSCN. In the optical spectrum of the red [OsCl5(SCN)]2? the charge-transfer S→Os is nearly constant at 538 nm, but the N→Os transition of the yellow to violet coloured N-isomer shifts from 480 nm in organic solvents or in presence of large alkylammonium cations to 516 nm in aqueous solution and to 544 nm in the solid Cs-salt. The optical electronegativities are calculated to χopt(–SCN) = 2.6 and χopt(–NCS) = 2.6–2.8. According to spinorbit coupling and to lowered symmetry (C4v) the splitted intraconfigurational transitions are observed at 10 K as weak peaks in the regions 600, 1000 and 2000 nm. The O? O transitions are calculated from the vibrational fine structure. The lowest level of both isomers is confirmed by peaks in the electronic raman spectra. With the parameters ζ(OsIV) = 3200 cm?1 and B(? SCN) = 316 cm?1 or B(? NCS) = 288 cm?1 there is a good fit of calculated and experimental data, resulting in the nephelauxetic series: F? > CI? > SCN? > Br? > NCS? > I?. |
