High-Nuclearity Lanthanide(III) Complexes as Single-Molecule Magnets and Luminescent Materials

Abstract

The employment of the bridging/chelating Schiff base ligands, N-salicylidene-o-aminophenol (saphH2), N-salicylidene-o-aminocyclohexanol (sachH2) and N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2), in lanthanide (LnIII) cluster chemistry has afforded four families of polynuclear and dinuclear complexes with new structural motifs, and interesting magnetic and optical properties. Chapter 1 deals with most of the fundamental aspects within the areas of polynuclear metal complexes, molecular magnetism and optics as these are applied to 4f-metal based systems, while the research results are reported in Chapters 2, 3 and 4. In the first project (Chapter 2), the coordination chemistry of the organic chelating/bridging ligand, N-salicylidene-o-aminophenol (saphH2) in lanthanide cluster chemistry was investigated. The general LnIII/X-/saphH2/base reaction system has led to a family of (NHEt3)[Ln7(OH)2(saph)10(Me2CO)2] (Ln = Gd (1); Tb (2); Dy (3)) clusters with a new core topology that comprises two {Ln4} butterflies sharing a common metal vertex. The {DyIII7} analogue exhibits slow magnetization relaxation, whereas all heptanuclear compounds show ligand-centered blue-green emissions. The second project of this thesis, which is discussed in Chapter 3, comprises the first use of the Schiff base ligand N-salicylidene-2-aminocyclohexanol (sachH2; mixture of cis- and trans-analogue) in metal cluster chemistry which has afforded a new family of [Ln7(OH)6(CO3)3(sach)3(sachH)3(MeOH)6] (Ln = Gd (4); Tb (5); Dy (6)) clusters with ideal D3h point group symmetry and metal-centered trigonal prismatic topology. Solid-state and solution studies revealed single-molecule magnetism (SMM) and photoluminescence behaviors. Moreover, in order to investigate the steric and stereoisomerism effects of the ligand on the chemical and structural identity of the {Ln7} clusters, the pure trans-analogue of the sachH2 ligand was utilized. As a result, a new family of octanuclear [Ln8(OH)4(CO3)2(trans-sach)8(EtOH)4] (Ln = Gd (7); Tb (8); Dy (9); Eu (10)) clusters were obtained, while the solid-state studies revealed SMM behavior and lanthanide-centered emissions. In the last chapter of this thesis (Chapter 4), the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2) was introduced for a first time in lanthanide cluster chemistry. This has afforded a family of dinuclear [Ln2(NO3)4(sacbH)2(H2O)2(MeCN)2] compounds (Ln = Gd (11); Tb (12); Dy (13)) with the Dy-analogue exhibiting SMM behaviour with a high-energy barrier for the magnetization reversal and interesting magnetization dynamics. All research-based Chapters (Chapters 2-4) are divided into subsections in order to facilitate the understanding of the research concepts by the familiar and non-familiar readers and contextualize the messages, goals and conclusions of each individual project. I felt it prudent to always begin with a short preface of the work that summarizes the most important aspects of the specific project, followed by the complete experimental part and discussion of the results, and finishing up with conclusions and some future perspectives.