Mixed nuclear complexes in both solution and crystal phases are widely studied as models for charge transfer (CT) reactions using advanced spectroscopical and electrochemical tools. We investigate the molecular structure of a Fe-Pt-Fe complex [(NC)6Fe-Pt(NH3)4-Fe(CN)6]4-, and related dinuclear and mononuclear model complexes, using first-principles based calculations. In contrast to earlier interpretations of the experiments, we find that the most stable solvated complex geometry is substantially varied from the crystal phase geometry, mainly due to differences in the underlying oxidation numbers of the metal centers. Specifically, in the crystal phase a Pt(IV) complex resulting from (Pt-to-Fe) backward electron transfers is stabilized by an octahedral ligand field. On the other hand, in the solution phase a Pt(II) complex with a square planar ligand field forms a CT salt by binding the iron complexes through long-range electrostatic interactions. The new assigned solution phase structure is shown to be consistent with spectroscopical data and measured CT rates. Interestingly, we find that the experimentally indicated photoinduced process in the solvated complex is of the backward CT (Pt-to-Fe). In the presentation we provide detailed benchmarking of our first-principles computational approach used to study spectroscopy and electron transfer rates of organic semiconducting molecular systems. The same protocol is used to unearth the structure-function relations of the widely studied Fe-Pt-Fe trimetal complex.

Spectroscopy and electron transfer processes in molecular systems of multi metal centers: Insight by ab-initio modeling

253rd National Meeting (2017)

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