Reductive quenching of the emission of trans-dioxo(1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)osmium(VI) in water

Siegfried Schindler, Ed Castner, Carol Creutz, Norman Sutin

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36 Citations (Scopus)

Abstract

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)O2 2+/OsV(tmc)O 2 + couple (kex = 1 × 105 M-1 s-1) and the aqua ion couple (aqua ion, kq): Fe(H2O)6 2+, 1.0 × 109 M-1 s-1; Co(H2O)6 2+, 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), CO3 2- (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 CO3 2-/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.

Original languageEnglish
Pages (from-to)4200-4208
Number of pages9
JournalInorganic Chemistry
Volume32
Issue number20
Publication statusPublished - 1993

ASJC Scopus subject areas

  • Inorganic Chemistry

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