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

摘要

This paper reports the experimental and theoretical investigations of two trigonal bipyramidal Ni(Ⅱ) complexes, [Ni(Me_6tren)Cl]-(CIO_4) (1) and [Ni(Me_6tren)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 D_(expt) value (energy difference between the M_s = ± 1 and M_s = 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 M_s = ± 1 and M_s = 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 D_(theor) between -100 and -200 cm~(-1)) is obtained.