Factors governing electronic localization in transition metal clusters and complexes

Abstract

Small nickel atom clusters exhibit an energetic preference for localized, open 3d-shells. This tendency is attributed to weak 3d-3d overlap and is analyzed in terms of the competition between resonance integrals and screening terms. Analogous competition between resonance and screening leads to (spatially) symmetry-broken charge-localized SCF solutions for 3d ion-hole states in nickel atom clusters. Charge-localized symmetry broken wavefunctions are also employed as initial and final diabatic (nonstationary) states in the electron transfer processes associated with transition metal complexes of the type MX, where M = Fe, Ru; X = H2O; NH3, n = 2, 3. Resonance integrals coupling the initial (reactants) and final (products) states have been calculated for several geometrical structures and electronic states of interest. An important contributor to the screening effects which promote charge localization in these systems is the charge-dependence of metal-ligand bond lengths. The decrease in oxidation-state dependence of metal-ligand bond length in the series Fe2+/3+ (H2O)6 → Ru2+/3+ (H2O)6 → Ru2+/3+ (NH3)6 is analyzed in terms of ligand-to-metal charge transfer (LMCT), and the trend is attributed to diminished participation of the metal atom in the redox process. The electronic rearrangement upon reduction is dominated by the eg (σ) manifold, even though the reducing electron is added to the t2g (π) manifold.