A high-performance dysprosium single-ion magnet with local pseudo cubic geometry

Abstract

The syntheses and magnetic characterizations of two eight-coordinated isostructural mononuclear complexes, [Ln(BPPA)₂]BPh₄·2CH₂Cl₂ (Ln = Dy, 1-Dy and Tb, 2-Tb; HBPPA = N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-bis(2-pyridylmethyl)amine), are reported. The eight-coordinate Ln(III) ions have a local pseudo cubic geometry, where two O atoms of the phenol groups are on the opposite sides with the short Ln(III)–O bonds and the O–Ln(III)–O angle of 180°. This geometrical feature results in a strong axial crystal field along the O–Ln(III)–O direction. Complex 1-Dy exhibits zero-field slow relaxation of magnetization with the peaks of out-of-phase susceptibilities (χ′′_M) up to 46 K. On applying a 1000 Oe dc field, the energy barrier to magnetic reversal for 1-Dy reaches 678(50) K, which even surpasses those of most of the reported square antiprism Dy(III) complexes. However, 2-Tb only shows weak χ′′_M signals without maxima under the extra dc field. It is worth noting that complex 1-Dy represents the first observation of zero-field slow relaxation behavior in the Ln(III) complexes with local cubic geometry. Ab initio computations carried out on both of them substantiate the difference in the magnetic properties of both complexes, which also reveal that the high energy barrier for 1-Dy was mainly caused by the axial short Dy–O distances.