CONFIGURATION-DEPENDENT ELECTRON HOPPING BETWEEN EQUIVALENT LIGANDS IN ISOMERIC RUTHENIUM(II) COMPLEXES

The three configurational isomers of [(bpy)Ru(abpy)(2)](2+), bpy = 2,2 '-bipyridine and abpy = 2,2'-azobis(pyridine), have been identified vi a H-1 NMR spectroscopy and crystal structure information from precurso r complexes. One-electron reduction introduces a single electron which can undergo site-exchange ('hopping') between the two equivalent abpy ligands in [(bpy)Ru-II(abpy(-I))(abpy(0))](.+). EPR line broadening a t higher temperatures indicates a slow-exchange situation which is mos t pronounced for the cct (alpha(1)) isomer with the coordinated azo gr oups in trans configuration; the EPR signal was broadened beyond recog nition at temperatures above 220 K. A less unusual behaviour was obser ved for the ccc (beta) and the new etc (alpha(2)) isomer, both with th e coordinated azo functions in cis-positions.