Direct Determination of Magnetic Anisotropies in Pnictinidenes and Fe(II) compounds from 3 to 6000 cm^-1 by THz-EPR Spectroscopy. – (Tarek Al Said / LNCMI / Seminar). – 5/02/2026, 14H

Seminar LNCMI

Tarek Al Said , Helmholtz-Zentrum Berlin für Materialien und Energie

Seminar LNCMI, 5/02/2026, 14H, Visio

Abstract
The magnetic anisotropy (zero-field splitting, ZFS) of a molecular compound is a sensitive probe for the electronic structure and can further present an important property of functional materials.
For example, probing the typically large ZFS in high-spin (HS) Fe(II) compounds, gives inside in the function of related metalloenzymes or spin-crossover (SCO) compounds [1,2].
In molecular magnetism, a large magnitude of the anisotropy is desired to increase the spin-reversal barrier [3].
For an accurate determination, electron paramagnetic resonance (EPR) spectroscopy is the method of choice, however large ZFS poses serve experimental challenges for conventional EPR methods.

To study species with large magnetic anisotropy, we employ frequency-domain Fourier-transform THz-EPR (FD-FT THz-EPR) spectroscopy at BESSY II [4] in a range from 3 to 6000 cm^-1 and at magnetic fields up to 10 T in conjunction with optical excitation.
In this talk, examples on recent research on HS main group and transition metal compounds will be given. First, we show the EPR characterization of two mononuclear HS Fe(II) complexes [5],
which serve as models for SCO compounds, and give an outlook on the possibilities to study thermally and light-induced SCO by THz-EPR.
Second, studies on different triplet pnictinidenes (R–Pn, Pn = As,Bi) reveal the influence of adjacent metal atoms and SOC on the electronic structure of metallo-arsinidenes (Pt– As, Pd–As) [6]
and demonstrate the determination of a giant axial ZFS of +5422 cm^-1 in a bismuthinidene (R–Bi) [7], to the best of our knowledge, the largest value experimentally determined up to now.

Thereby, our studies establish FD-FT THz-EPR as a unique method to probe very large ZFS in order to draw robust magneto-structural correlations with implications for new magnetic materials.

[1] A. Ozarowski et al., J. Am. Chem. Soc 2004, 126, 6574.
[2] P. Gütlich et al., Beilstein J. Org. Chem. 2013, 9, 342
[3] F. Neese and D. Pantazis, Faraday Discuss. 2011, 148, 229.
[4] J. Nehrkorn et al., J. Magn. Res. 2017, 280, 10.
[5] Manuscript in preparation
[6] M. Deben et al., J. Am. Chem. Soc 2025, 147, 5330.
[7] T. Al Said et al., J. Am. Chem. Soc 2025, 147, 84.

Lieu : Salle Pauthenet in Grenoble

Lien Zoom : 
https://univ-grenoble-alpes-fr.zoom.us/j/94228207316?pwd=khTdznxeFy1ZUYkYftQ0QSox6Fz3iK.1