Investigation of the Spectroscopic, Electrochemical, and Spectroelectrochemical Properties of Osmium(II) Complexes Incorporating Polyazine Bridging Ligands: Formation of the Os/Os and Os/Ru Mixed-Valence Complexes


A series of homobimetallic Os(II) complexes have been prepared of general formula [[(bpy)2Os]2(BL)]4+ (where BL = bridging ligand and bpy = 2,2′-bipyridine). The bridging ligands used were 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq), and 2,3-bis(2-pyridyl)benzoquinoxaline (dpb). The compounds' electrochemical, spectroscopic, and spectroelectrochemical properties have been studied and comparisons have been made with previously prepared Os/Ru heterobimetallic and Ru/Ru homobimetallic complexes incorporating the same bridging ligands. The lowest energy electronic transitions in these homometallic systems have been assigned as Os(dπ) BL(π*) 1MLCT transitions. On the basis of spectroelectrochemical experiments, assignments for the electronic absorption spectra have been made. The Os(II)/Os(III) and Os(III)/Ru(II) mixed-valence complexes of this series of ligands have been prepared. These mixed-valence systems display rich near-infrared spectra. Values for the extent of electron delocalization between the metal centers, α2, range from 2.7 × 10−3 to 1.0 × 10−2, which indicates that these systems are much more weakly coupled Robin and Day class II systems than has been previously implied through electrochemical analysis.

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Inorganic Chemistry