Molecular
Structure, Spectroscopy, and Photoinduced
Kinetics in Trinuclear Cyanide Bridged Complex in Solution: A First-Principles
Perspective
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Abstract
We
investigate the molecular structure of the solvated complex,
[(NC)<sub>6</sub>Fe–Pt(NH<sub>3</sub>)<sub>4</sub>–Fe(CN)<sub>6</sub>]<sup>4–</sup>, and related dinuclear and mononuclear
model complexes using first-principles calculations. Mixed nuclear
complexes in both solution and crystal phases were widely studied
as models for charge transfer (CT) reactions using advanced spectroscopical
and electrochemical tools. In contrast to earlier interpretations,
we find that the most stable gas phase and solvated geometries are
substantially different from the crystal phase geometry, mainly due
to variance in the underlying oxidation numbers of the metal centers.
Specifically, in the crystal phase a Pt(IV) metal center resulting
from Fe ← Pt backward electron transfers is stabilized by an
octahedral ligand field, whereas in the solution phase a Pt(II) metal
complex that prefers a square planar ligand field forms a CT salt
by bridging to the iron complexes through long-range electrostatic
interactions. The different geometry is shown to be consistent with
spectroscopical data and measured CT rates of the solvated complex.
Interestingly, we find that the experimentally indicated photoinduced
process in the solvated complex is of backward CT (Fe ← Pt)