A central issue in the rational design of artificial photosynthetic systems is determining the factors that tune the reduction potentials, thermodynamics, and kinetics of the photosensitizer, the oxygen evolving complex (OEC) and hydrogen evolving complex (HEC) catalysts. Although density functional theory (DFT) calculations in particular can be utilized to make useful predictions about the thermodynamics, kinetics, and mechanisms of the OEC and HEC reactions, application of uncalibrated DFT approaches could easily give rise to false conclusions. In order to gain accurate chemical and physical properties for computational screening of the catalysts, we have assessed a series of recently developed density functionals in conjunction with the experimental results of X-ray crystallography and photoelectron spectroscopy of [M(mnt)2]n- (M = Fe, Co, Ni; mnt = 1,2-S2C2(CN)2; n = 1,2). The optimized DFT method (M06/DZVP2) produced values in accordance with the experimental ones. Using this calibrated method, we examined the structures, spin states, redox properties, and thermodynamics of [1Co], [2Co], and [4Co] Co-OEC analogues with 4- and 6-coordinated cobalt by the broken-symmetry approach. These results reveal a correlation between the spin state and the geometric features of analogues; the calculated structures and electronic properties are also in agreement with experimental observations. Furthermore, we found that the oxidized [Co4O4] may have a different electronic structure, thus leading to different reactivities for water splitting reactions.

Probing structures, spin states, redox properties, and thermodynamics of Co-OEC analogs using broken-symmetry density functional theory

251st National Meeting (2016)

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