Electron-transfer chemistry of the luminescent excited state of trans-dioxo-osmium(VI)

Abstract

Excitation of trans-dioxo-osmium(VI) complexes in the solid state and in fluid solutions at room temperature at 350–400 nm results in red emission with maxima at 620–710 nm. Rate constants for electron-transfer quenching of trans-[Os^VI(L¹)O₂]^2+*(L¹= 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane) and trans-[Os^VI(L⁴)O₂]^2+*{L⁴=meso-2,3,7,11,12-pentamethyl-3,7,11,17-tetra-azabicyclo[11.3.1 ]heptadeca-1 (17),13,15-triene} by a series of structurally related aromatic hydrocarbons with varying redox potentials have been determined in acetonitrile. The ³E_g states of trans-[Os^VI(L¹)O₂]²⁺ and trans-[Os^VI(L⁴)O₂]²⁺ are powerful one-electron oxidants, the excited-state reduction potentials of which in acetonitrile, E°(Os^VI*–Os^V), have been found to be 2.39(10) and 2.00(10) V vs. normal hydrogen electrode respectively, which agree well with estimations using spectroscopic and electrochemical data.