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Giant Ising-Type Magnetic Anisotropy in Trigonal Bipyramidal Ni(II) Complexes: Experiment and Theory

Ruamps, Renaud, Maurice, Rémi, Batchelor, Luke, Boggio-Pasqua, Martial, Guillot, Régis, Barra, Anne Laure, Liu, Junjie, Bendeif, El-Eulmi, Pillet, Sébastien, Hill, Stephen, Mallah, Talal, Guihéry, Nathalie
Journal of the American Chemical Society 2013 v.135 no.8 pp. 3017-3026
bromine, electron paramagnetic resonance spectroscopy, energy, nickel
This paper reports the experimental and theoretical investigations of two trigonal bipyramidal Ni(II) complexes, [Ni(Me₆tren)Cl](ClO₄) (1) and [Ni(Me₆tren)Br](Br) (2). High-field, high-frequency electron paramagnetic resonance spectroscopy performed on a single crystal of 1 shows a giant uniaxial magnetic anisotropy with an experimental Dₑₓₚₜ value (energy difference between the Mₛ = ± 1 and Mₛ = 0 components of the ground spin state S = 1) estimated to be between −120 and −180 cm–¹. The theoretical study shows that, for an ideally trigonal Ni(II) complex, the orbital degeneracy leads to a first-order spin–orbit coupling that results in a splitting of the Mₛ = ± 1 and Mₛ = 0 components of approximately −600 cm–¹. Despite the Jahn–Teller distortion that removes the ground term degeneracy and reduces the effects of the first-order spin–orbit interaction, the D value remains very large. A good agreement between theoretical and experimental results (theoretical Dₜₕₑₒᵣ between −100 and −200 cm–¹) is obtained.