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 via H-1 NMR spectroscopy and crystal structure information from precursor 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 at higher temperatures indicates a slow-exchange situation which is most pronounced for the cct (alpha(1)) isomer with the coordinated azo groups in trans configuration; the EPR signal was broadened beyond recognition at temperatures above 220 K. A less unusual behaviour was observed for the ccc (beta) and the new etc (alpha(2)) isomer, both with the coordinated azo functions in cis-positions.