Tales of a lepidopterist: using amine polyalcohol ligands in the development of novel heterometallic single-molecule magnets

Martin, Robert Christopher (2024) Tales of a lepidopterist: using amine polyalcohol ligands in the development of novel heterometallic single-molecule magnets. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The synthesis and characterisation of a series of thirty complexes is reported, based upon the binding of symmetric or asymmetric amine polyalcohol ligands to a predicted {TM2-Ln2} core. All reactions proceeded via serendipitous self-assembly and thereby exhibit both designed and unexpected topologies. These topologies range from trimetallic partial butterflies to icosidyometallic propeller-like complexes. Magnetic susceptibility measurements were carried out on thirteen of the thirty complexes to assess their value as potential single-molecule magnets (SMMs). Fourteen complexes were synthesised using N,N-bis(2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid ([DIPSO]H4) as the primary structural ligand. Single crystal X-ray diffraction (SC-XRD) data is provided for each of these structures, thirteen of which are novel. Six of these compounds form as the intended {3d-4f} butterfly motif, whilst the remaining eight exhibit various other topologies. Magnetic data was collected for four of the samples, however no out-of-phase χ” signals were observed down to 2 K. The attempted syntheses of the seven asymmetric amine polyalcohol ligands, 3-[(2-hydroxyethyl)(methyl)amino] propan-1-ol, [HMAP]H2, 3-[(2-hydroxyethyl)(ethyl)amino] propan-1-ol, [HEAP]H2, 3-[(2-hydroxyethyl)(iso-propyl)amino] propan-1-ol, [HiPrAP]H2, 3-[(2-hydroxyethyl)(phenyl)amino] propan-1-ol, [HPhAP]H2, 3-[(2-hydroxyethyl)(tert-butyl)amino] propan-1-ol, [HtBuAP]H2, 3-[(2-hydroxyethyl)(adamantyl)amino] propan-1-ol, [HAdAP]H2, 2,2’-[(3-hydroxypropyl)imino] bis-ethanol, [nPr’DEA]H3, are described. Additionally, the syntheses of precursor molecules and their symmetric variants are also described, for a total of twenty-one precursor or pro-ligand molecules. Four of the seven target ligands are fully characterised, whilst the final three remain partially characterised. Syntheses proceeded by stepwise amine alkylations in non-polar media as to prevent reaction cascades common in conventional non-catalysed amine alkylation reactions. Six reactions utilising synthesised asymmetric polyalcohol ligands with a {3d} metal source and {4f} metal source proceeded by serendipitous self-assembly to produce five novel complexes and one toroidal complex. Two of these complexes inhabit the traditional {3d-4f} butterfly motif, two exhibit a {TM2Ln2} buckled core akin to the butterfly motif, one monomeric and one in a chain form. The final novel complex exhibits a square-in square type topology. Magnetic data was collected for three of the samples, of which two complexes, [CrIII2DyIII2(OMe)2(Benz)4(HMAP)2(NO3)2] and [CrIII2DyIII2(OMe)2(Benz)4(HEAP)2(NO3)2], exhibited open hysteresis loops up to 3.5 K, with maximum coercive fields of 2.5 T and 2.98 T at their lowest measured temperatures, respectively. Similarly, nine reactions utilising synthesised symmetric and asymmetric ligands with a {4d} metal source and a {4f} metal source were performed to produce one known butterfly, seven novel butterflies and one {Ru2Dy4} extended butterfly. A novel {5p-4f} complex was also synthesised forming an unusual propeller-like motif of formula [InIII16DyIII6(O)6(OH)12(OMe)3(Benz)22(HMAP)6(NO3)5]. Magnetic data was collected for six of the samples, two of which, [RuIII2DyIII2(OMe)2(Benz)4(MDEA)2(NO3)2] and [RuIII2DyIII2(OMe)2(2-Cl-4,5-F-Benz)4(MDEA)2(NO3)2], revealed clear frequency and temperature dependant maxima in their out-of-phase components, indicative of SMM behaviour.