NONEMPIRICAL AB-INITIO STUDIES ON INNER-SPHERE REORGANIZATION ENERGIES OF M(2+)(H2O)(6) M(3+)(H2O)(6) REDOX COUPLES AT VALENCE BASIS LEVEL/

On the basis of the basic feature of the electron transfer reactions, a new theoretical scheme and application of a nonempirical ab initio m ethod in computing the inner-sphere reorganization energies (RE) of hy drated ions in electron transfer processes in solution are presented a t valence STO basis (VSTO) level. The potential energy surfaces and th e various molecular structural parameters for transition metal complex es are obtained using nonempirical molecular orbital (MO) calculations , and the results agree very well with experimentally observed ones fr om vibrational spectroscopic data. The results of inner-sphere REs obt ained from these calculations via this new scheme give a good agreemen t with photoemission experimental findings and those from the improved self-exchange model proposed early for M(2+) (H2O)(6)/M(3+)(H2O)(6)(M = VI,Cr, Mn, Fe, and Co) redox couple systems and are better than tho se from semiempirical INDO/II MO method and other classical methods. F urther, the observed agreement of the optimized structural data and th e results of inner-sphere REs of complexes with experimental findings confirms the following: (1) the validity of nonempirical MO calculatio n method to get accurate structural parameters and inner-sphere RE for the redox systems for which reliable vibrational spectroscopic data a re not available, (2) the validity of the improved self-exchange model proposed early for inner-sphere RE, and (3) the reasonableness of som e approximations adopted in this study. (C) 1997 John Wiley & Sons, In c.