Mixed-valence complexes strengths

The Electronic Interaction Term. A question raised earlier was is the magnitude of J sufficiently small to justify the weak-interaction assumption This is a question which can be answered, at least for mixed-valence complexes, by interpretation of the oscillator strength of the intervalence band. In Table III, some data (24, 25) for the intervalence band of the... 

There are at least two ways in which detailed information about electron-vibrational coupling strengths can be obtained for mixed-valence complexes. Both are based on the fact that such coupling will be reflected in modifications of the vibrational spectrum. Thus, for example, coupling to antisymmetric modes in a symmetric ion will modify intensities and frequencies of the modes involved. 

Hush applied Mulliken s theories of the transition dipole moment of charge transfer bands to the specific question of IT bands in mixed-valence complexes. By equating theoretical and experimental expressions for /, where / is the oscillator strength of the intervalence band, it is possible to derive an expression for metal-metal coupling (//ad). 

The oxidation of [(NH3)5Ru (pyr)Ru (edta)] by S20g is biphasic. The first phase results in information of the mixed valence species, [(NH3)5Ru (pyr)Ru (edta)] , with a rate constant 2.5 x 10 Af s . From rate comparisons with the corresponding monomeric complexes this is thought to proceed with initial formation of [(NH3)5Ru (pyr)Ru (edta)] followed by rapid intramolecular electron transfer. The second phase consists of two pathways. One pathway is independent of [S20g ] and involves dissociation of the mixed-valence adduct, followed by rapid oxidation of [(NH3)5Ru (pyr)] . The second pathway involves oxidation of the adduct and has a rate constant 5.5x 10 M s at 25.0 °C and 0.10 M ionic strength. Kinetics of the oxidations of [Fe(phen)3] and [Fe(bpy)3] " by S20g have also been reported. Two pathways are involved. In one, ligand dissociation precedes the oxidation, while the other involves an outer-sphere adduct from which an inner-sphere intermediate is formed. 

The optical activity in valence excitations of chiral metal complexes has been effectively treated using the model of an achiral chromophore (metal ion) in a chiral environment (ligands) and this model appears also appropriate for XAS in view of the core nature of the initial orbital state. The zero-order electric and magnetic transition moments arise from different transitions and must be mixed by some chiral environmental potential (V ). Considering the case of a lanthanide ion, and taking tihe electric dipole transitions for the Z.2,3 edge as Ip—Kj), a first-order perturbation expression for the rotational strength looks like ... 

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