Magnetospectroscopic Studies of a Series of Fe(II) Scorpionate Complexes: Assessing the Relationship between Halide Identity and Zero-Field Splitting

Authors

Daniel J. Santa Lucia, Institute for Chemical Energy
Laxmi Devkota, Marquette University
Sergey Lindeman, Marquette University
Andrew Ozarowski, Florida State University
J. Krzystek, Florida State University
Mykhaylo Ozerov, Florida State University
Samuel M. Greer, Florida State University
Daniel C. Cummins, University of Delaware
Klaus H. Theopold, University of Delaware
Mihail Atanasov, Max-Planck-Institut für Kohlenforschung
Joshua Telser, Roosevelt University
Adam T. Fiedler, Marquette UniversityFollow

Document Type

Article

Publication Date

8-11-2025

Publisher

American Chemical Society

Source Publication

Inorganic Chemistry

Source ISSN

0020-1669

Original Item ID

DOI: 10.1021/acs.inorgchem.5c02691

Abstract

Ferrous ions in four-coordinate environments are common in protein structures, synthetic catalysts, and molecular magnets. The 3d⁶ configuration of high-spin Fe(II) imparts an S = 2 ground state, whose analysis using conventional spectroscopic methods is often hindered by substantial zero-field splitting (ZFS). Herein, we provide detailed electronic-structure descriptions for [Fe^IIX(Tp^tBu,Me)] (1-X; X = F, Cl, Br, I), where (Tp^tBu,Me)− is hydrotris(3-tert-butyl-5-methyl-pyrazol-1-yl)borate. The three pyrazolyl N-donors of the “scorpionate” ligand facially coordinate to Fe(II), giving idealized C_3v symmetry with the halide occupying the axial position. Although originally reported by Theopold and co-workers, this series is revisited herein using advanced experimental and theoretical tools. Ground-state transitions were probed by high-frequency and -field electron paramagnetic resonance (HFEPR) and far-infrared magnetic spectroscopy (FIRMS). Variable-temperature/-field (VTVH) ⁵⁷Fe Mössbauer spectroscopy, paramagnetic susceptibility, and VTVH reduced magnetization were also utilized. This combined approach provided complete sets of spin-Hamiltonian parameters. Interpretation using ab initio multiconfigurational calculations enabled quantification of halide-dependent magnetoelectronic effects. Jahn–Teller distortions induce a descent in symmetry from C_3v to C_s in both solution and solid state. Finally, we demonstrate that the 1-X series is ionic, with the ZFS arising from combined Jahn–Teller and ligand field effects, rather than intrinsic spin–orbit coupling from the halides.

Comments

Inorganic Chemistry, Vol. 65, No. 31 (August 11, 2025): 16135-16151. DOI.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Recommended Citation

Santa Lucia, Daniel J.; Devkota, Laxmi; Lindeman, Sergey; Ozarowski, Andrew; Krzystek, J.; Ozerov, Mykhaylo; Greer, Samuel M.; Cummins, Daniel C.; Theopold, Klaus H.; Atanasov, Mihail; Telser, Joshua; and Fiedler, Adam T., "Magnetospectroscopic Studies of a Series of Fe(II) Scorpionate Complexes: Assessing the Relationship between Halide Identity and Zero-Field Splitting" (2025). Chemistry Faculty Research and Publications. 1107.
https://epublications.marquette.edu/chem_fac/1107