Configuration-dependent electron hopping between equivalent ligands in isomeric ruthenium(II) complexes

Abstract

The three configurational isomers of [(bpy)Ru(abpy)₂]²⁺, bpy = 2,2′-bipyridine and abpy = 2,2′-azobis(pyridine), have been identified via¹H 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^–1)(abpy⁰)]˙⁺. EPR line broadening at higher temperatures indicates a slow-exchange situation which is most pronounced for the cct(α₁) 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(β) and the new ctc(α₂) isomer, both with the coordinated azo functions in cis-positions.