Influence of alcoholic solvent and acetate anion coordination mode variations on structures and magnetic properties of heterometallic Zn2Dy2 tetranuclear clusters

Abstract

The present work clarifies how slight modifications of the synthetic conditions (e.g., employment of different alcoholic solvents) can result in the variation of the coordination mode of an acetate anion yielding two structurally similar heterometallic Zn₂Dy₂ tetranuclear clusters with formulas [Zn₂Dy₂(L)₄(CH₃COO)₂(CH₃CH₂OH)₂]·2CH₂Cl₂·0.5H₂O (1) and [Zn₂Dy₂(L)₄(CH₃COO)₂(CH₃OH)₂]·4CH₂Cl₂·2CH₃OH·0.1H₂O (2), where H₂L is (E)-4-(tert-butyl)-2-((2-hydroxy-3-methoxybenzylidene)amino)phenol. Complexes 1 and 2 were synthesized by varying the alcoholic solvent employed in the synthesis. The ethanol solvent in 1 led to the acetate anion being coordinated to the Dy^III ion in bidentate chelating mode while the methanol solvent in 2 generated the acetate anion coordinated to the Dy^III ion in bridging mode. Such a subtle change of the coordination mode of the acetate anion on the Dy^III ion imposes a significant effect on the distinct dynamic relaxation in 1 and 2. The magnetic properties of 1 and 2 were characterized through SQUID magnetometry and theoretical calculations to determine the effective energy barrier, energy levels, magnetic anisotropy and intracluster magnetic exchange coupling parameters. Both tetramers show frequency dependence of the out-of-phase ac magnetic susceptibility signal under zero applied dc field associated with single-molecule magnetic behaviour. The effective energy barriers of 1 and 2 are 115.4 and 104.2 cm⁻¹, respectively. Theoretical calculations suggest that the different magnetic behaviours between 1 and 2 are mainly due to the coordination mode variations of the acetate anion on the Dy^III site. The present result highlights how a subtle modification in the reaction alcoholic solvent resulted in two structurally similar tetranuclear Zn₂Dy₂ examples with different magnetic behaviours.