ASPECTS OF INTERVALENCE CHARGE-TRANSFER IN CYANIDE-BRIDGED SYSTEMS - MODULATED ELECTRIC-FIELD ASSESSMENT OF DISTANCES, POLARIZABILITY CHANGES, AND ANTICIPATED FIRST HYPERPOLARIZABILITY CHARACTERISTICS

Electroabsorption studies of the systems (CN)(5)M-II-CN-M'(III)(NH3)(5 )(1-) (M = Fe, Ru, Os; M' = Ru, Os) reveal that the metal-to-metal or intervalence charge-transfer transitions are associated with a change in dipole moment, \Delta mu\, ranging from 11 to 17 D. This change cor responds to a charge-transfer distance of ca. one-half to two-thirds o f the geometric separation between the donor and acceptor metals. This result has consequences for electron transfer parameters, where elect ronic coupling energies are now upwardly revised to as high as 3000 cm (-1). The result is also pertinent in the context of nonlinear optics, where Delta mu can be utilized in a two level model to estimate wavel ength-dependent molecular first hyperpolarizabilities. The change in p olarizability (Delta alpha) accompanying the optical intervalence tran sitions varies from -10 to +310 Angstrom(3). Comparing the experimenta l results to a simple two state model suggests that the two state pict ure is seriously deficient for these systems and that a multitude of a vailable additional states must be included to achieve a quantitative description of the polarizable intervalence excited states of these sy stems.