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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

   https://doi.org/10.1002/chem.202100705  

   Bone, Alexandria_N; Widener, Chelsea_N; Moseley, Duncan_H; Liu, Zhiming; Lu, Zhengguang; Cheng, Yongqiang; Daemen, Luke_L; Ozerov, Mykhaylo; Telser, Joshua; Thirunavukkuarasu, Komalavalli; et al (August 2021, Chemistry – A European Journal)

   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 andu‐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 theS=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) andgvalues. 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 inCo‐X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spin‐phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling. 

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2. Magnetic anisotropies and slow magnetic relaxation of three tetrahedral tetrakis(pseudohalido)–cobalt( ii ) complexes

   https://doi.org/10.1039/D1NJ01916C  

   Chen, Shu-Yang; Lv, Wei; Cui, Hui-Hui; Chen, Lei; Zhang, Yi-Quan; Chen, Xue-Tai; Wang, Zhenxing; Ouyang, Zhong-Wen; Yan, Hong; Xue, Zi-Ling (September 2021, New Journal of Chemistry)

   Three mononuclear tetrakis(pseudohalido)-cobalt( ii ) complexes (Ph 4 P) 2 [Co(E) 4 ] (E = N 3 − , 1; NCO − , 2; NCS − , 3) have been synthesized and structurally characterized. Each compound contains a distorted tetrahedral Co 2+ ion coordinated by four pseudohalide ligands. The magnetic properties of 1–3 have been studied using direct-current magnetic measurements and high-frequency and -field EPR spectroscopy (HFEPR), suggesting easy-axis magnetic anisotropy for 1 and 2 and easy-plane anisotropy for 3. Analysis of the HFEPR spectra yielded D values of −5.23 and +3.63 cm −1 for 2 and 3, respectively. The absence of the EPR signal in 1 is consistent with a large, negative value of the zero-field splitting (ZFS) parameter D in 1. The nature of magnetic anisotropies of 1–3 has also been confirmed by ab initio calculations. The calculated D values are consistent with those determined using magnetometry and HFEPR studies. Alternating current (AC) magnetic susceptibilities reveal slow magnetic relaxation under an applied magnetic field, thus indicating that 1–3 are field-induced single-ion magnets (SIMs). 

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3. Quantum electronic control on chemical activation of methane by collision with spin–orbit state selected vanadium cation

   https://doi.org/10.1039/D0CP04333H  

   Ng, Cheuk-Yiu; Xu, Yuntao; Chang, Yih-Chung; Wannenmacher, Anna; Parziale, Matthew; Armentrout, P. B. (January 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   By coupling a newly developed quantum-electronic-state-selected supersonically cooled vanadium cation (V + ) beam source with a double quadrupole-double octopole (DQDO) ion–molecule reaction apparatus, we have investigated detailed absolute integral cross sections ( σ 's) for the reactions, V + [a 5 D J ( J = 0, 2), a 5 F J ( J = 1, 2), and a 3 F J ( J = 2, 3)] + CH 4 , covering the center-of-mass collision energy range of E cm = 0.1–10.0 eV. Three product channels, VH + + CH 3 , VCH 2 + + H 2 , and VCH 3 + + H, are unambiguously identified based on E cm -threshold measurements. No J -dependences for the σ curves ( σ versus E cm plots) of individual electronic states are discernible, which may indicate that the spin–orbit coupling is weak and has little effect on chemical reactivity. For all three product channels, the maximum σ values for the triplet a 3 F J state [ σ (a 3 F J )] are found to be more than ten times larger than those for the quintet σ (a 5 D J ) and σ (a 5 F J ) states, showing that a reaction mechanism favoring the conservation of total electron spin. Without performing a detailed theoretical study, we have tentatively interpreted that a weak quintet-to-triplet spin crossing is operative for the activation reaction. The σ (a 5 D 0 , a 5 F 1 , and a 3 F 2) measurements for the VH + , VCH 2 + , and VCH 3 + product ion channels along with accounting of the kinetic energy distribution due to the thermal broadening effect for CH 4 have allowed the determination of the 0 K bond dissociation energies: D 0 (V + –H) = 2.02 (0.05) eV, D 0 (V + –CH 2 ) = 3.40 (0.07) eV, and D 0 (V + –CH 3 ) = 2.07 (0.09) eV. Detailed branching ratios of product ion channels for the titled reaction have also been reported. Excellent simulations of the σ curves obtained previously for V + generated by surface ionization at 1800–2200 K can be achieved by the linear combination of the σ (a 5 D J , a 5 F J , and a 3 F J ) curves weighted by the corresponding Boltzmann populations of the electronic states. In addition to serving as a strong validation of the thermal equilibrium assumption for the populations of the V + electronic states in the hot filament ionization source, the agreement between these results also confirmed that the V + (a 5 D J , a 5 F J , and a 3 F J ) states prepared in this experiment are in single spin–orbit states with 100% purity. 

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4. Synthesis and magnetic studies of pentagonal bipyramidal metal complexes of Fe, Co and Ni

   https://doi.org/10.1039/c8dt05074k  

   Deng, Yi-Fei; Yao, Binling; Zhan, Peng-Zhi; Gan, Dexuan; Zhang, Yuan-Zhu; Dunbar, Kim R. (March 2019, Dalton Transactions)

   Three mononuclear metal complexes [M II (L-N 3 O 2 )(MeCN) 2 ][BPh 4 ] 2 (M = Fe, 1 ; Co, 2 ; Ni, 3 ) were isolated and structurally characterized. Magnetic studies revealed uniaxial magnetic anisotropy for 1 ( D = −17.1 cm −1 ) and 3 ( D = −14.3 cm −1 ) and easy-plane magnetic anisotropy for 2 ( D = +36.9 cm −1 ). Slow magnetic relaxation was observed for complexes 1 and 2 under an applied magnetic field, both of which are dominated by a Raman process. 

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5. Square-planar Co( iii ) in {O ₄ } coordination: large ZFS and reactivity with ROS

   https://doi.org/10.1039/c8cc04464c  

   Steele, Jennifer L.; Tahsini, Laleh; Sun, Chen; Elinburg, Jessica K.; Kotyk, Christopher M.; McNeely, James; Stoian, Sebastian A.; Dragulescu-Andrasi, Alina; Ozarowski, Andrew; Ozerov, M.; et al (October 2018, Chemical Communications)

   Oxidation of distorted square-planar perfluoropinacolate Co compound [Co II (pin F ) 2 ] 2− , 1 , to [Co III (pin F ) 2 ] 1− , 2 , is reported. Rigidly square-planar 2 has an intermediate-spin, S = 1, ground state and very large zero-field splitting (ZFS) with D = 67.2 cm −1 ; | E | = 18.0 cm −1 , ( E / D = 0.27), g ⊥ = 2.10, g ‖ = 2.25 and χ TIP = 1950 × 10 −6 cm 3 mol −1 . This Co( iii ) species, 2 , reacts with ROS to oxidise two (pin F ) 2− ligands to form tetrahedral [Co II (Hpfa) 4 ] 2− , 3 . 

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