Infrared, resonance-Raman, and excitation profile studies of [Os2(O2CCH2Cl)4Cl2], [Os2(O2CC2H5)4Cl2], and [Os2(O2CC3H7)4Cl2]: assignment of osmium–osmium, osmium–oxygen, and osmium–chlorine stretching vibrations

Abstract

Detailed Raman (1 600–35 cm–1) and Fourier-transform i.r. (3 500–40 cm–1) studies of the diosmium tetracarboxylate complexes [Os2(O2CR)4Cl2](R = CH2Cl, C2H5, or C3H7), coupled with related earlier studies of [Os2(O2CCH3)4Cl2] and [Os2(O2CCD3)4Cl2], have provided a basis for the identification of the three Raman-active (a1g) bands ν1, ν2, and ν3 at 236–228, 393–256, and 311–292 cm–1 respectively, to the key skeletal fundamentals ν(OsOs), ν(OsO), and ν(OsCl), respectively. Thus, while both ν(OsOs) and ν(OsCl) are relatively insensitive to the carboxylate R group, ν(OsO) is, as expected, highly sensitive thereto. Raman studies at resonance with the intense near-ultraviolet electronic band (406–383 nm) of each complex yields resonance-Raman spectra in each case characterised by the development of three overtone progressions in ν1. These reach 6ν1, 4ν1+ν2, and 4ν1+ν3 at most. The results are typical of A-term resonance-Raman scattering. The depolarisation ratio of the ν1 band at resonance with the ca. 390 nm band demonstrates that the latter arises from an axially polarised transition, consistent with an earlier assignment π(Cl)→π*(Os2).