title: Magneto-structural investigations of N/O chelate ligands in 3d metal clusters
Creators: name: Agapaki, Eleftheria
Publisher: name: The University of Edinburgh
Year: 2025
Subjects: subject: Magneto-structural
subject: Chelate ligands
subject: 3d metal clusters
subject: Ferromagnetic/Antiferromagnetic interactions
subject: Single molecule magnets (SMM)

description: Magnetic materials are ubiquitous in modern society, finding applications across information technology, healthcare and transport. The move to molecule-based magnets looks to exploit the quantum nature of molecules for quantum technologies, including quantum computing. Before any such application can be made practical chemists must first make and physically characterise the proposed molecules in order to develop detailed magneto-structural correlations. The first stage in this process is ligand design. Amongst the most successful choices are N/O chelate ligands. These ligands are small and flexible, possessing the ability to both chelate and bridge metal centres. This has led to the isolation and characterisation of numerous paramagnetic 3d transition metal clusters ranging in nuclearity, oxidation state and topology. Chapter 1 summarises the most impactful N/O-supported 3d metal clusters reported in the literature, discussing the magnetic properties they display. These include single molecule and singe ion magnets, clusters displaying large spin ground states, enhanced magneto-caloric effects and geometric spin frustration. Chapter 2 describes the synthesis and characterisation of a series of [Mᴵᴵ₄] cubanes (M = Mn, Co‒Zn) and the larger nuclearity clusters [Mnᴵᴵᴵ₂Mnᴵᴵ₁₂] and [Mnᴵᴵᴵ₁₄Mnᴵᴵ₄], built with (3,5-dimethyl-1H-pyrazol-1-yl)methanol (HL¹), and a [Niᴵᴵ₁₄] wheel supported by 3,5-dimethylpyrazole (HL²). Magnetic measurements for the cubanes reveal ferro- and antiferromagnetic exchange interactions for M = Ni, Cu and M = Mn, Co, respectively, the origin of the differences being the different M-O-M angles. Competing exchange interactions are present in [Mn₁₈] and [Mn₁₄], with the former possessing SMM behaviour. [Ni₁₄] displays ferromagnetic nearest neighbour exchange interactions leading to a S=14 ground state. DFT calculations are consistent with the experimental magnetic measurements, revealing the importance of the bridging Cl ions in determining the sign of the exchange. Chapter 3 reports the synthesis and characterisation of a family of [Mnᴵᴵᴵ₂Mnᴵᴵ₂] butterflies, two [Mnᴵᴵᴵ₃Mnᴵᴵ₄] clusters with different topologies and a novel [Mnᴵᴵᴵ₁₂Mnᴵᴵ₈] cluster that consists of two supertetrahedra. All are supported by (1-methyl-1H-imidazol-2-yl)methanol (HL3). Magnetic studies reveal that butterflies and one of the [Mn₇] clusters possess both ferro- and antiferromagnetic exchange interactions, with three of the butterflies being SMMs, while the [Mn₇] Anderson Wheel displays dominant ferromagnetic exchange interactions. The [Mn₂₀] cluster can be described as two ferromagnetic {Mn₁₀} supertetrahedra, coupled mutually by a weak antiferromagnetic interaction, which leads to an enhanced magnetocaloric effect. Chapter 4 details the synthesis and characterisation of novel odd- [Feᴵᴵᴵ₁₁Mᴵᴵ₄] and even- [Feᴵᴵᴵ₁₂Mᴵᴵ₄] numbered wheels (Mᴵᴵ = Co, Zn), supported by the ligand triethanolamine. Magnetic susceptibility and magnetization measurements on the Zn analogues revealed strong antiferromagnetic interactions leading to a frustrated S = 1/2 ground state in the former and a S = 0 ground state in the latter. Chapter 5 summarises the main findings of the thesis and identifies areas for future study and growth.