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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.

 

Two five-coordinate mononuclear Co( ii ) complexes [Co(12-TMC)X][B(C 6 H 5 ) 4 ] (L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC), X = Cl − ( 1 ), Br − ( 2 )) have been studied by X-ray single crystallography, magnetic measurements, high-frequency and -field EPR (HF-EPR) spectroscopy and theoretical calculations. Both complexes have a distorted square pyramidal geometry with the Co( ii ) ion lying above the basal plane constrained by the rigid tetradentate macrocyclic ligand. In contrast to the reported five-coordinate Co( ii ) complex [Co(12-TMC)(NCO)][B(C 6 H 5 ) 4 ] ( 3 ) exhibiting easy-axis anisotropy, an easy-plane magnetic anisotropy was found for 1 and 2 via the analyses of the direct-current magnetic data and HF-EPR spectroscopy. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements demonstrated that complexes 1 and 2 show slow magnetic relaxation at an applied dc field. Ab initio calculations were performed to reveal the impact of the terminal ligands on the nature of the magnetic anisotropies of this series of five-coordinate Co( ii ) complexes. 

Reaction of CCl4 with zirconium amide guanidinate Zr(NMe2)2[iPrNC(NMe2)NiPr]2 (1) has been found to give ZrCl(NMe2)[iPrNC(NMe2)NiPr]2 (2) as an intermediate and later ZrCl2[iPrNC(NMe2)NiPr]2 (3). The reaction is likely radical in nature. Complex 2 has been independently prepared from the reaction of ZrCl(NMe2)3 with 2 equiv of diisopropylcarbodiimide, iPr-N=C=N-iPr, and characterized by NMR and elemental analysis. 

Trigonal bipyramidal Ni(II) complex [Ni(Me6tren)Cl](ClO4) (1, Me6tren = tris[2-(dimethylamino)ethyl]amine) has recently been shown by Ruamps and coworkers to possess large, uniaxial magnetic anisotropy (J. Am. Chem. Soc. 2013, 135, 3017). Their HF-EPR studies gave rhombic zero-field-splitting (ZFS) parameter E = 1.56(5) cm-1 for 1. However, the axial ZFS parameter D has not been determined. We have used far-IR magnetic spectroscopy (FIRMS) at 0-17.5 T and 5 K to probe the magnetic transitions between the MS = 1 and MS = 0 states of the ground spin state S = 1 in 1. Direct observation of the transitions between Zeeman-split states in FIRMS give axial ZFS parameter D = -110.7(3) cm-1. Hirshfeld surface analysis of the crystal structure of 1 has been performed, revealing the interactions between the cation and anion in a molecule of 1 as well as among the molecules of 1 in crystals.