Abstract (TEA)[OSCl6] is formed quantitatively by heating solid trans-(TEA)[OsX4(CO)2] (X = Br, I) in a stream of chlorine at 120 °C, and can be purified by recrystallisation from CH2Cl2 without decomposition. It is reduced immediately by acetone, methanol, Cl-, Br-, I- to give [OsCl6]2-. The standard potential [OsCl6]-/[OsCl6]2- in acetonitrile referred to the saturated mercury-mercurous sulphate electrode is 0.840 V. The IR and Ra bands of (TEA)[OsCl6], assigned according to point group Oh, are shifted to higher frequencies compared with (TEA)2[OsCl6]. The excitation at 488.0 nm gives a resonance Raman spectrum exhibiting 6 overtones of vi and combination tones up to 4ν1 + v5. The electronic absorption spectrum shows five spin-forbidden intraconfigurational transitions coupled with odd vibrational modes in the near infrared region. The spin-allowed 4A2g → 4T2g,4T1g-transitions are observed at 347 and 305 nm. The excited levels can be fitted with the parameters ⊿ = 28500 cm-1, B = 340 cm-1, ξ = 2500 cm-1 , allowing to calculate the nephelauxetic ratio β55 to 0.47. In the visible region extensive charge transfer transitions are observed. Based on the strong oxidizing character of Os(V) there is a bathochromic shift of corresponding bands of [OsCl6]- in relation to [OsCl6]2- of about 6600 cm-1 and to the isoelectronic [ReCl6]2- of about 13700 cm-1, respectively. From πt1u→dt2g the optical electronegativity is calculated to Xopt(Osv) = 2.49.
Benzene-fused bis(acenaphthoBODIPY)s, stable near-infrared-selective dyes
