Christopher Chang - Computational Chemical Analysis of [FeFe] Hydrogenase H-Cluster Analogues To Discern Catalytically Relevant Features of the Natural Diatomic Ligand Configuration.

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  Chang, C.H. (2011) J. Phys. Chem. A  115(31): 8691-704


  Density functional theoretical models of the electronic structure   of several configurational isomers and analogues of the   [2Fe]H H-cluster in [FeFe] hydrogenase were analyzed   to identify distinguishing features of the canonical cofactor   structure potentially relevant to catalysis. Collective analysis   of geometric changes over models of oxidized and reduced [2Fe]   clusters highlighted movement of the bridging carbonyl and   anticorrelation of the proximal and distal   Fe-Cterminal bonds as key explanatory factors for   variance over the considered models. Charge and bond order   analysis suggest that as the bridging carbonyl favors the distal   iron upon reduction, bonding simultaneously becomes more ionic in   nature, raising the possibility of simple electrostatic   stabilization as a factor in charge accumulation prior to   ultimate H2 creation and release. Frontier orbital   energies show cis and trans arrangements of   cyanide on the Fe‒Fe core to have distinctive energies from the   other models, which may be important for redox poise. Altogether,   few factors qualitatively distinguish the cis- from the   trans-cyano configurations, which may in fact enhance   catalytic robustness under conditions leading to exchange of the   bridging and terminal carbonyl ligands. However, the naturally   occurring trans configuration possesses two distinct   donor-metal-acceptor S‒Fe‒C(O) interactions, which might play a   role in enforcing a low-spin ground state for the hydridic   mechanism of H2 production.

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