1. Applying Unconventional Spectroscopies to the Single‐Molecule Magnets, Co(PPh 3 ) 2 X 2 (X=Cl, Br, I): Unveiling Magnetic Transitions and Spin‐Phonon Coupling
- Author
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Samuel M. Greer, Azar Aliabadi, Zhiming Liu, Dmitry Smirnov, Luke L. Daemen, Stephen Hill, Yongqiang Cheng, Mykhaylo Ozerov, Zi-Ling Xue, Joshua Telser, Kim R. Dunbar, Zhengguang Lu, J. Krzystek, Karsten Holldack, Alexander Schnegg, Duncan H. Moseley, Komalavalli Thirunavukkuarasu, Chelsea N. Widener, and Alexandria N. Bone
- Subjects
Coupling ,010405 organic chemistry ,Chemistry ,Phonon ,Organic Chemistry ,Relaxation (NMR) ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Molecular physics ,Catalysis ,Inelastic neutron scattering ,0104 chemical sciences ,law.invention ,law ,Magnet ,Condensed Matter::Strongly Correlated Electrons ,Ground state ,Electron paramagnetic resonance ,Spin (physics) - Abstract
Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single-molecule magnets (SMMs). Spin-phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin-phonon coupling in molecules is challenging. We have found that far-IR magnetic spectra (FIRMS) of Co(PPh3)2X2 (Co-X; X = Cl, Br, I) reveal rarely observed spin-phonon coupling as avoided crossings between magnetic and u-symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and Phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero-field split (ZFS) levels of the S = 3/2 electronic ground state were probed by INS, high-frequency and -field EPR (HFEPR), FIRMS, and frequency-domain FT terahertz EPR (FD-FT THz-EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) and g values. Ligand-field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities in Co-X, showing that the larger Co(II) spin density in a molecule is, the larger its ZFS magnitude is. The current work reveals dynamics of magnetic and phonons excitations in SMMs. Studies of such couplings in the future would help understand how spin-phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling.
- Published
- 2021