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)benzoquinoxatine (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(dpi) --> BL(pi*) 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, alpha2, range from 2.7 X 10(-3) to 1.0 X 10(-2), which indicates that these systems are much more weakly coupled Robin and Day class 11 systems than has been previously implied through electrochemical analysis.