A highly conducting tetrathiafulvalene-tetracarboxylate based dysprosium(iii) 2D metal–organic framework with single molecule magnet behaviour

Abstract

The synthesis and whole characterization by a multitechnique approach of an unprecedented dysprosium(III) 2D metal organic framework (MOF), involving the redox-active tetrathiafulvalene (TTF)-based linker TTF-tetracarboxylate (TTF-TC), are herein reported. The single-crystal X-ray structure, formulated as [Dy₆(TTF-TC)₅(H₂O)₂₂]·21H₂O (1), reveals a complex 2D topology, with hexanuclear Dy₆ clusters as secondary building units (SBUs) interconnected by five linkers, stacked almost parallel in each layer and eclipsed along the [111] direction, leading to the formation of 1D channels filled by water molecules. The mixed valence of the TTF units is confirmed by both bond distance analysis, Raman microscopy and diffuse reflectance spectroscopy, and further supported by band structure calculations, which also predict activated conductivity for this material. Thanks to efficient TTF stacking and partial oxidation, 1 shows semiconducting behavior, with, however, a record conductivity value of 1 mS cm⁻¹ at room temperature, when compared to the previously reported TTF-based MOFs. Furthermore, temperature and magnetic field dependent ac (alternative current) magnetic susceptibility measurements demonstrate field induced slow relaxation of magnetization, accounting for two independent relaxation processes, with an energy barrier (U_eff/K) of around 12 K, typical for dysprosium carboxylate complexes. The herein reported 2D Dy-MOF provides a valuable master plan for coexistence of conducting π-TTF stacks and highly anisotropic Dy^III SMM properties.