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Updated: May 25, 2025
Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
Published on: June 9, 2023
A Spectroscopic Criterion for Identifying the Degree of Ground-Level Near-Degeneracy Derived from Effective
Wang Chen1,2, Nikolai Kochetov3,4, Thomas Lohmiller4,5
1State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China.
Abstract:
The fascinating magnetic and catalytic properties of coordinatively unsaturated 3d metal complexes are a manifestation of their electronic structures, in particular their nearly doubly or triply degenerate orbital ground levels. Here, we propose a criterion to determine the degree of degeneracy of this class of complexes based on their experimentally accessible magnetic anisotropy (parametrized by the electron spin g- and zero-field splitting (ZFS)-tensors). The criterion is derived from a comprehensive spectroscopic and theoretical study in the trigonal planar iron(0) complex, [(IMes)Fe(dvtms)] (IMes = 1,3-di(2',4',6'-trimethylphenyl)imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane, 1). Accurate ZFS-values (D = +33.54 cm-1, E/D = 0.09) and g-values (g ∥ = 1.96, g ⊥ = 2.45) of the triplet (S = 1) ground level of complex 1 were determined by complementary THz-EPR spectroscopy and SQUID magnetometry. In-depth effective Hamiltonian (EH) analyses coupled to wave-function-based ab initio calculations show that 1 features a ground level with three energetically close-lying orbital states with a "two-above-one" energy pattern. The observed magnetic anisotropy results from mixing of the two excited electronic states with the ground state by spin-orbit coupling (SOC). EH investigations on 1 and related complexes allowed us to generalize this finding and establish the anisotropy of the - and ZFS-tensors as spectroscopic markers for assigning two- or three-fold orbital near-degeneracy.
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