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Title: Molecule-based magnetic materials of the ReIV ion
Author: Pedersen, Anders Hjordt
ISNI:       0000 0004 7224 694X
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2017
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The [ReCl6]2-, [ReBr6]2- and [ReCl4(ox)]2- anions are crystallised with the organic 4,4’- bipyridinium dication (4,4-H2bipy). Magnetometry reveals exotic behaviour of the [4,4’- H2bipy][ReCl6] and [4,4’-H2bipy][ReBr6] salts which demonstrate spin-canting, antiferromagnetic exchange interactions and metamagnetism. Single crystal X-ray structures at T = 3, 14 and 20 K of the [4,4’-H2bipy][ReBr6] salt reveal the behaviour to be purely of magnetic origin as no structural changes are observed. For the [4,4’-H2bipy][ReCl4(ox)] compound an antiferromagnetic exchange interaction of 10.2 cm-1 between the anions is observed (Chapter 2). The complexes (NBu4)2[(ReCl5)2(μ-pyrazine)], (NBu4)2[(ReBr5)2(μ-pyrazine)], (NBu4)2[(ReBr5)2(μ-pyrimidine)] and (NBu4)2[(ReBr5)2(μ-triazine)] are structurally and magnetically characterised in Chapter 3. Magnetic measurements reveal the ReIV ions bridged by a 1,4-heterocyclic amine to exhibit strong antiferromagnetic coupling induced by the linearity of the bridging ligand. The two dimers bridged by a 1,3-heterocyclic amine exhibit intramolecular ferromagnetic exchange and at low temperature an intermolecular antiferromagnetic coupling is observed for the (NBu4)2[(ReBr5)2(μ-triazine)] complex due to the presence of short intermolecular Br···Br distances. Six molecular ReIVCuII chains of formula {[Cu(L)4][ReCl6]}n (L = imidazole, 1- methylimidazole, 1-vinylimidazole, 1-butylimidazole, 1-vinyl-1,2,4-triazole or dimethylformamide) are characterised structurally and magnetically in Chapter 4. SQUID magnetometry and theoretical calculations reveal the chains to exhibit ferromagnetic exchange interactions, which increase as the Re–Cl–Cu bond angle decreases. The {[Cu(vinylimidazole)4][ReCl6]}n chain exhibit magnetic order at TC = 2.4 K, and the {[Cu(imidazole)4][ReCl6]}n network exhibits ferrimagnetic behaviour. Eight complexes of the [ReCl6]2- and [ReBr6]2- anions crystallised with the [MII(L•)2]2+ (M = Fe, Co or Cu) or [Ni(L•)(CH3CN)3]2+ cations (L• = 4-dimethyl-2,2-di(2-pyridyl)oxazolidine N-oxide) are characterised structurally and magnetically in Chapter 5. The [Co(L•)2]2+ cation shows evidence of a gradual, thermally induced spin-crossover transition in variable-temperature magnetic and structural experiments. The [Ni(L•)(CH3CN)3]2+ cation show exchange of the coordinated acetonitrile molecules for atmospheric water upon drying. The nickel-radical magnetic coupling is ferromagnetic in all cases, demonstrating spin-canting behaviour with an ordering temperature of T = 2.7 K for the [ReCl6]2- based compound, and intermolecular antiferromagnetic exchange interactions for the [ReBr6]2- based complex.
Supervisor: Brechin, Euan ; Inglis, Ross Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: ReIV ions ; antiferromagnetic coupling ; ferromagnetic exchange interactions ; spin-canting ; metamagnetism