The Influence of Ligand Substitution at the Electron Donor Center in Molecular Cyano‐Bridged Mixed‐Valent Co III /Fe II and Co III /Ru II Complexes

In this paper we report a new variety of dinuclear cyano‐bridged Co III /M II (M = Fe or Ru) mixed‐valent complexes of the general formula [L n Co III (μ‐NC)M II (CN) x (bpy) y ] z + (where L n represents a pentaamine macrocycle and M = Fe or Ru with x = 4, y = 1 and z = 1 or x = 2, y = 2 and z = 3)]. The incorporation of the bpy ligand in place of cyano ligands within the coordination sphere raises the M III/II redox potential significantly relative to the hexacyanometalate analogs we have reported previously. However, the metal‐to‐metal (M II to Co III ) charge‐transfer transitions are shifted to lower energies in accordance with Hush theory as a result of a decreased reorganizational energy component, which result in them overlapping with more intense MLCT (M II to bpy) transitions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)