Spin‐State‐Dependent Properties of an Iron(III) Hydrogenase Mimic

Abstract

AbstractA biomimetic mononuclear iron(III) model complex was investigated in detail by density functional theory (DFT) calculations. Structural and energetic criteria were employed to confirm the S = 3/2 intermediate state to be the ground state. The ground state was verified by using both pure and hybrid functionals with different amounts of exact Hartree–Fock exchange. A comprehensive study of the influence of the functional as well as thermodynamic corrections to the energetic ordering of spin states was performed. A modified B3LYP functional with 10 % Hartree–Fock exchange was able to reproduce the structural properties in excellent agreement with the experimental data. The thermodynamics of two possible spin‐crossover transitions [intermediate‐spin to high‐spin (IS–HS) and low‐spin to high‐spin (LS–HS)] were investigated. A torsional profile obtained by rotation of the axial ligand revealed a spin‐dependent preference of the ligand orientation. The structure solved by X‐ray crystallography corresponds to the global energetic minimum of the complex in the S = 3/2 and 5/2 states but not in the S = 1/2 state. This study demonstrates that the spin multiplicity affects not only the structural properties but may also influence the chemical reactivity of this transition metal complex in general.