Reductive quenching of the red emission of the metal-centered excited state of the title osmium(VI) complex (0.3 mM, lifetime 1.0 µs) has been characterized in water at 25 °C (0.5 M ionic strength). The excited state is a very strong oxidant and is very rapidly quenched by a number of moderately reducing anions (anion, 10−9kq, M−1 s−1): NO2−, 2.0; N3−, 4.0; I−, 6.5. The rate constants for quenching by aqua ions are in fair agreement with values calculated from the Marcus cross-relation and self-exchange rates for the *OsVI(tmc)O22+/Osv(tmc)O2+ couple (kex = 1 × 105 M−1 s−1) and the aqua ion couple (aqua ion, kq): Fe(H2O)62+, 1.0 × 109 M−1 s−1; Co(H2O)62+, 1.0 × 106 M−1 s−1; CeIII(aq), ≤1.0 × 105 M−1 s−1. The kq (M−1 s−1) values for quencher (Q) = Cl− (4 × 105), HCO2− (1.5 × 106), Br−(1.7 × 108), SCN−(5.6 × 109), CO32− (1.6 × 108), and OH− (1.0 × 107) are used to estimate self-exchange rate constants for the Q+/Q couples. The first estimates are presented for the CO32−/CO3− (0.4 M−1 s−1), OH·/OH− (300 M−1 s−1), and HCO2/HCO2− (300 M−1 s−1) couples. Self-exchange rates for the X·/X− halogen couples, calculated assuming that only the outer-shell barrier contributes to the intrinsic barrier to outer-sphere electron transfer and that a two-sphere dielectric continuum model is applicable, are orders of magnitude smaller than the self-exchange rates inferred from the quenching data and literature data.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry