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

International audienceThis 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