Nonempirical ab initio studies on inner-sphere reorganization energies of M2+(H2O)6/M3+(H2O)6 redox couples at valence basis level

Abstract

On the basis of the basic feature of the electron transfer reactions, a new theoretical scheme and application of a nonempirical ab initio method in computing the inner-sphere Ž . reorganization energies RE of hydrated ions in electron transfer processes in solution Ž . are presented at valence STO basis VSTO level. The potential energy surfaces and the various molecular structural parameters for transition metal complexes are obtained Ž . using nonempirical molecular orbital MO calculations, and the results agree very well with experimentally observed ones from vibrational spectroscopic data. The results of inner-sphere REs obtained from these calculations via this new scheme give a good agreement with photoemission experimental findings and those from the improved 2q Ž . . and Co redox couple systems and are better than those from semiempirical INDOrII MO method and other classical methods. Further, the observed agreement of the optimized structural data and the results of inner-sphere REs of complexes with Ž . experimental findings confirms the following: 1 the validity of nonempirical MO calculation method to get accurate structural parameters and inner-sphere RE for the Ž . redox systems for which reliable vibrational spectroscopic data are not available, 2 the Ž . validity of the improved self-exchange model proposed early for inner-sphere RE, and 3

Quantum chemical calculations of the reorganization energy of blue‐copper proteins

“…Several other groups have tried to calculate the reorganization energy for transition metal complexes or proteins (Churg et al, 1983;Zhou & Khan, 1989;Yadav et al, 1991;Bu et al, 1994;Larsson et al, 1995;Bu et al, 1997;Soriano et al, 1997). In particular, Larsson et al (1995) have tried to estimate the innersphere reorganization energy for azurin and plastocyanin using crystal structures and simple harmonic potential for the metal ligand bonds.…”

The orientation and distance-dependence analysis of the electron transfer reactivity: An electron correlation level investigation of Mn2+(H2O)2/Mn3+(H2O)2 system

“…Our theoretically optimized bond lengths at the UMP2(full)/6‐311+G* level are 2.0054 Å [Mn 2+ (H 2 O) 2 ] and 1.9115 Å [Mn 3+ (H 2 O) 2 ] for the Mn–oxygen separation ( r Mn–O ); they are obviously smaller than that (2.0479 Å) of Mn + (H 2 O) 2 calculated by Rosi and Bauschlicher at the electron correlation level using the modified coupled pair functional method with a larger basis set 3. These values are smaller than those of the corresponding hexaaquo ions found experimentally in the crystal state [2.17 Å; in Mn 2+ (H 2 O) 6 and 1.99 Å in Mn 3+ (H 2 O) 6 ] 8. Obviously, this observation is reasonable, because two ligands in the dihydrated species are generally placed at two sides of the metal ion, and the ligand–ligand repulsion interaction is smaller than that in the hexaaquo systems and, therefore, the attraction interaction of Mn 2+ or Mn 3+ for two H 2 O molecules in the dihydrated species is stronger than that in the hexaaquo system.…”

“…Extensive theoretical work has recently been devoted to the understanding of the structures, the properties, and the chemical reactivities of the saturated and the unsaturated molecular species1–10 involving transition metal ions. This is particularly true for the electron transfer (ET) reaction and its related processes involving transition metal ions, because the ET or the charge transfer (CT) processes involving transition metal ions are embodied in many areas of research such as the environment, biochemistry, materials, and the living things.…”

“…These theoretical calculations have offered an attractive alternative to experiment for determining the spectroscopic constant and the bond energies of transition metal systems. Many accurate calculations are now available for both the neutrals and ions of the first‐ and second‐row transition metal compounds 1–10. To our knowledge, no experimental data and theoretical investigation exist for any of the charged transition metal di‐hydrates with higher ionic valent states (such as +2, +3).…”

Theoretical Study of V2+OH2/V3+OH2 Electron Transfer Reactivity at Electron Correlation Level

“…Electron transfer (ET) reactions in solution are very complicated reactions, − not only because there are many complicated surrounding factors which influence the ET rate and mechanism, but also because there are many structural factors from the reactant molecules themselves. − It is well-known that the transition metal coordination ions in solution keep some complex equilibrium. For the hydrated V 2+ ion (V 2+ (aq)), there coexist several coordination equilibria…”