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Darstellung, spektroskopische und elektrochemische Charakterisierung von Pentachloromonocarbonylosmat(IV), [OsCl5(CO)]- / Preparation, Spectroscopical and Electrochemical Characterization of Pentachlorom onocarbonylosm ate(IV), [OsCl5(CO)]-

1986; De Gruyter; Volume: 41; Issue: 1 Linguagem: Inglês

10.1515/znb-1986-0106

1865-7117

Michael Bruns, W. Preetz,

Metal complexes synthesis and properties

The first carbonyl compound of quadrivalent osmium [OsCl 5 (CO)] - is prepared by chlorination of trans-[OsX 4 (CO) 2 ] - (X = Br, I) dissolved in CH 2 Cl 2 . It is reduced immediately by Br - and I - to give [OsCl 5 (CO)] 2- . The standard potential [OsCl 5 (CO)] - / [OsCl 5 (CO)] 2- in acetonitrile referred to the saturated mercury-mercurous sulphate electrode is 0.623 V. The IR and Ra bands of [OsCl 5 (CO)] - are assigned according to point group C 4v . Compared with the corresponding Os(III) complex there is a shift to higher frequencies of ν(CO) and ν(OsCI) of about 170 and 25 cm -1 , whereas ν(OsC) and δ(OsCO) are lowered by 158 and 110cm -1 , respectively. The electronic absorption spectrum shows six d - d bands coupled with vibrations in the near infrared region. The O - O transitions are calculated from the vibrational fine structure, taking into consideration shifts by 13 C isotopic substitution. The lowest levels are confirmed by peaks in the electronic Raman spectrum. From the estimated Racah parameter B = 280 cm -1 the low nephelauxetic ratio β 55 = 0.41 is deduced indicating the high covalency in [OsCl 5 (CO)] - . Owing to the strong oxidizing character of Os(IV) the intensive charge transfer transitions in the visible region are shifted bathochromicly by about 4000 cm 1 in relation to corresponding bands of [OsCl 5 (CO)] 2- .