Electroabsorption studies of intervalence charge transfer in (NC)₅FeCNOs(NH₃)₅: Experimental assessment of charge-transfer distance, solvent reorganization, and electronic coupling parameters

Electroabsorption studies of (NC)₅FeCNOs(NH₃)₅^- show that light-induced metal-to-metal charge transfer is accompanied by a dipole moment change of -12.5 ± 1.5 D along the charge-transfer axis. This change corresponds to an effective one-electron transfer distance of 2.5 ± 0.3 A, i.e., less than half the geometric distance from iron to osmium. The charge-transfer distance revision has profound effects upon estimates for solvent reorganization and nonadiabatic electronic coupling energies. The distance revision decreases the former from 7000 to 2200 cm^-1 and increases the latter from 1260 to 2600 cm^-1. Reliable estimates for both, of course, are required in order to understand light-induced electron-transfer kinetics.