Intraconfigurational, trip-multiplet, and anomalously polarised A(1g) and A(2g) transitions in electronic and vibrational resonance Raman spectra of (spin-degenerate) trans-di(cyano)phthalocyaninatorhenates

Brown bis(tetra(n-butyl)ammonium) trans-di(cyano)-phthalocyaninato(2-)rhena te(II) (1) is prepared by melting bis(phthalocyaninato(2-)rhenium(II)) with tetra(n-butyl)ammonium cyanide. According to electrochemical data, 1 is ox idised by iodine to yield blue tetra(n-butyl)ammonium trans-di(cyano)phthal ocyaninato(2-)rhenate(III) (2), whose cation exchange in the presence of bi s(triphenylphosphine)iminium salts has been confirmed by x-ray structure de termination. 1 and 2 dissolve without dissociation of the cyano ligands in cone. sulfuric acid. Dilution with cold water precipitates blue trans-di(cy ano)phthalocyaninato(2-)rhenium(III) acid. 1 and 2 are oxidised by bromine yielding violet trans-di(cyano)phthalocyaninato(1-)rhenium(III). Oxidation of 2 with dibenzoylperoxide and N-chlorsuccinimide is described. 1 and 2 ar e characterised by polarised resonance Raman(RR) spectra, FIR/MIR spectra, and UV-Vis-NIR spectra. Due to a Kramers degenerate ground electronic state of low-spin Re-II, a polarisation anomaly of the totally symmetric vibrati ons a(1g) at 598 and 672 cm(-1) with depolarisation ratios rho(1) > 3 is ob served in the RR spectra of 1. Weak bands in the unusual UV-Vis-NIR spectru m of 1, starting at 10200 cm(-1), are attributed to trip-multiplet (TM) tra nsitions. An electronic RR effect is detected for 2. The selectively enhanc ed anomalously polarised line at 1009 cm(-1) with rho(1) approximate to 15 and the (de)polarised lines between 1688 and 2229 cml are attributed to int raconfigurational transitions A(1g)-->A(2g)>A(1g), B-1g, B-2g, E-g arising from the T-3(1g) ground electronic state of low-spin Re-III split by spin-o rbit coupling and low symmetry (D-4h(*)). Some of their vibronic bands are detected in the IR spectrum between 1900 and 4000 cm(-1). B and Q transitio ns of 2 at 16700 and 31900 cm(-1), respectively, as well as eight weak TM t ransitions are observed between 5050 and 26100 cm(-1).