Redox behavior of dimeric bis(1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane) dicopper(I)/monomeric(1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane)copper(II) couple: detection of a metastable dimeric Cu(II)

The redox behavior of structurally constrained bis(1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane)dicopper (I)/(1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane)copper(II) couple was examined in acetonitrile: gated ET was observed even for this dimeric Cu(I)/monomeric Cu(II) couple. A dicopper(II) intermediate with a high-energy tetrahedral coordination geometry was spectrophotometrically identified for the first time for copper(II)/(I)-polypyridine redox couples. A low-intensity but low-energy LMCT band observed for the metastable dicopper(II) species indicates that gated ET process involves participation of a superexchange preceded by the deformation of ground-state Cu(II)N4 (in trigonal bipyramidal or D2d symmetry) to Cu(II)N4 with a teterahedral geometry.