EPR Spectroscopy of [Fe2O2(5-Et3-TPA)2]3+:  Electronic Origin of the Unique Spin-Hamiltonian Parameters of the Fe2 III,IVO2 Diamond Core

• Published in: Inorganic chemistry 2003-10, Vol.42 (20), p.6489-6496
• Main Authors: Skulan, Andrew J, Hanson, Melissa A, Hsu, Hua-fen, Dong, Yanhong, Que, Lawrence, Solomon, Edward I
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic034170z

The electronic origins of the magnetic signatures of [Fe2O2(5-Et3-TPA)2](ClO4)3, where 5-Et3-TPA = tris(5-ethyl-2-pyridylmethyl)amine, were investigated by density functional calculations. These signatures consist of a near-axial EPR spectrum, anisotropic superhyperfine broadening upon 17O substitution in the Fe2O2 core, and an unusually large, positive zero-field splitting parameter, D = 38 ± 3 cm-1. Density functional calculations identify the anisotropic 17O superhyperfine broadening to be due to a preponderance of oxo 2p density perpendicular to the plane of the Fe2O2 core in the three singly occupied molecular orbitals of the S = 3/2 ground state. The near-axial g-matrix arises from ΔS = 0 spin−orbit mixing between the singly and doubly occupied dπ orbitals of the iron d-manifold. The large D is due to ΔS = ±1 spin−orbit mixing with low-lying dπ excited states. These experimental observables reflect the dominance of iron−oxo (rather than Fe−Fe) bonding in the Fe2O2 core, and define the low-lying valence orbitals responsible for reactivity.