Linear intervalence transitions

Using the resonance Raman effect, Hester and Nour have assigned the Fe(II) -> Co(III) intervalence transitions in the complexes [(NC)5Fe(II)CNCo(III)(CN)5] and [(NC)5Fe(II)CNCo(III)(edta)f . Detailed analysis of the CN stretching modes also confirms the ground state valency assignments as shown. In the linear chain complexes [Pt(LL)2][Pt(LL)2X2]X4 (LL = diamine, X = Br or l ) the Pt(II)-Pt-Pt(IV) intervalence band is coupled to the symmetrical stretch, X-Pt-X of the Pt(IV) units, as in other complexes of this type. 

The simplest model consists of two centres, one donor (D) and one acceptor (A), separated by a distance I and contains two electrons. Here we consider this simple system to illustrate some general relations between charge transfer, transition intensities and linear as well as non-linear optical polarizabilities. We will show below that the electro-optic parameters and the molecular polarizabilities may be described in terms of a single parameter, c, that is a measure of the extent of coupling between donor and acceptor. Conceptually, this approach is related to early computations on the behaviour of inorganic intervalence complexes (Robin and Day, 1967 Denning, 1995), Mulliken s model for molecular CT complexes (Mulliken and Pearson, 1969) and a two-form/two-state analysis of push-pull molecules (Blanchard-Desce and Barzoukas, 1998). 

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