Polynuclear 3d/4f-Metal Complexes as Molecular Magnetic Refrigerants and Single-Molecule Magnets

Abstract

The use of two different chelating/bridging ligands, naphthalene-2,3-diol (ndH2) and acenaphthenequinone dioxime (acndH2), in heterometallic 3d/4f-metal cluster chemistry has yielded two new families of polynuclear CuII/LnIII clusters. These complexes were found to exhibit interesting magnetic properties, specifically single-molecule magnetism and the magnetocaloric effect. In this thesis, Chapter 1 lays the foundation for the research presented within. This section covers the fundamentals of polynuclear metal complexes, molecular magnetism, and the magnetocaloric effect, as well as the approaches used for the synthesis of new polynuclear metal complexes and the choice of ligands. Chapters 2 and 3 report the results of the current thesis. In Chapter 2, the synthesis and characterization of a family of {Cu4Ln} complexes (LnIII = GdIII (1), TbIII (2), DyIII (3)), employing the ligand ndH2 is presented. The complexes join a handful of previously reported {Cu4Ln} clusters, however, the family reported in this thesis are the first ‘propeller’-like clusters that exhibit single-molecule magnetism and magnetic refrigeration properties. In Chapter 3, a family of {Cu6Ln2}n chains (LnIII = GdIII (4), TbIII (5), DyIII (6)) obtained through the employment of ligand acndH2 is presented. This family of 1D-chains is a novel motif that has not been previously reported in the literature, with only a few discrete {Cu6Ln2} 0D-clusters having been previously reported. The complexes were magnetically characterized, with 4 and 5 exhibiting ferromagnetic exchange interactions while 6 revealed a more complex magnetic behaviour with both ferromagnetic and antiferromagnetic interactions dominating at different temperature regimes. Furthermore, 5 was found to behave as a single-molecule magnet and 4 was shown to act as a molecular magnetic refrigerant.