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 (a_1g) 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).