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-[OsVI(L1)O2]2+* (L1 = 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane) and trans-[OsVI (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 3Eg states of trans-[OsVI(L1)O2]2+ and trans-[OsVI(L4)O2]2+ are powerful one-electron oxidants, the excited-state reduction potentials of which in acetonitrile, E°(OsVI*-OsV), 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.