Tuning the slow magnetic relaxation with the substituents in anilate bridged bis(dysprosium) complexes

Abstract

Dinuclear lanthanide complexes [((HB(pz)₃)₂Dy)₂(μ-Th₂An)] (1Dy) and [((HB(pz)₃)₂Dy)₂(μ-ClCNAn)] (2Dy), based on the hydrotris(pyrazol-1-yl)borate (HBpz₃⁻) scorpionate capping ligand and anilate (An²⁻) bridging linkers, namely homosubstituted dithiophene- and heterosubstituted chlorocyanoanilate, bearing electron-donating and withdrawing substituents at the 3,6-positions of the benzoquinone core, are reported. 1Dy shows an octacoordinated {N₆O₂} Dy^III ion within a D_4h distorted square antiprismatic coordination, an ideal geometry for Single-Molecule Magnet (SMM) behavior, given its oblate nature, whereas in 2Dy the octacoordinated Dy^III ion adopts a D_2d triangular dodecahedron geometry, while maintaining the same {N₆O₂} coordination sphere. Both complexes show field-induced single molecule magnet (SMM) behaviour, with tuning of the slow magnetic relaxation as a function of the nature of the substituents at the 3,6-positions of the anilate moiety. A comparison of the Arrhenius fitting parameters for 1Dy and 2Dy supports the hypothesis that square antiprismatic Dy^III complexes, as 1Dy, exhibit higher energy barriers. This interpretation is supported by ab initio calculations that also shed light on the crucial role of intermolecular dipolar interactions.