Probing the need for a very low axial zero-field splitting in MnII systems with slow relaxation of the magnetization

Abstract

The effect of very small anisotropy on the slow relaxation of the magnetization was analysed for two series of structurally related Mn^II complexes with a trans-octahedral or trigonal bipyramid environment. Complexes with the formula [MnX₂(S,S-L1)], where L1 is a neutral tetradentate Schiff base and X = NCS⁻ (1_NCS), Cl⁻ (2_Cl), Br⁻ (3_Br), and I⁻ (4_I), and [MnX₂(L2)], where L2 is a neutral tridentate Schiff base and X = Cl⁻ (5_Cl) and Br⁻ (6_Br), and 1D [Mn(N₃)₂(L2)]_n (7) systems were characterized. Benefiting from the increasing spin orbit coupling (SOC) contribution of heavier halide donors in complexes 1–6, the gradation of the axial zero-field splitting parameter (D) was determined to be between ∼0.1 and 0.6 cm⁻¹ by EPR spectroscopy. Changing current measurements showed that the slow relaxation of the magnetization vanishes for larger D values, evidencing the crucial effect of D values of ∼0.2 cm⁻¹.