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Title: A study of the magnetic anisotropy in a family of 3d trigonal bipyramidal complexes
Author: Hay, Moya Anne
ISNI:       0000 0004 7963 0928
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2019
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The use of DABCO (1,4-Diazabicyclo[2.2.2]octane) and [MDABCO]+ (Methyl-4-aza-1-azoniabicyclo[2.2.2]octanium cation) as monodentate ligands for the synthesis of mononuclear trigonal bipyramidal (TBP) 3d transition metal complexes has been explored. The aim is to investigate their magneto-structural correlations in order to better understand their applicability as single-molecule magnets, and to inform the design of future molecular magnetic materials. Magneto-structural correlations in a series of Mn(II) mononuclear complexes MnCl3(HDABCO)(DABCO)] (1), [MnBr3(HDABCO)(DABCO)] (2), [MnCl3(MDABCO)2]·[ClO4] (3), and [MnCl3(H2O)(MDABCO)] (4) have been investigated using SQUID magnetometry and ab initio calculations, with a strategy to increase the magnetic anisotropy in complexes of this type revealed through in silico studies. A series of Fe(II) complexes [FeCl3(MDABCO)2]·[ClO4] (5), [FeCl3(H2O)(MDABCO)] (6), and [FeCl3(HDABCO)2]·[Cl] (7) were examined through various magnetic studies, and in the case of 5 also ab initio calculations. Geometrical distortions were probed and related to the contribution from 1st order spin-orbit coupling to the magnetic anisotropy in these systems, and the manifestation of single-ion magnet behaviour. Five Co(II)-based complexes are discussed herein - [CoCl3(DABCO)(HDABCO)] (8), [Co(NO3)3(H2O)(HDABCO)] (9), [Co(NO3)3(H2O)(MDABCO)] (10), [ZnxCo1-x(NO3)3(H2O)(HDABCO)] (11), and [ZnxCo1-x(NO3)3(H2O)(MDABCO)] (12) where x ~ 0.9. For complex 8, extensive high-field high-frequency electron paramagnetic (EPR) and frequency domain magnetic resonance (FDMR) experiments, corroborated with ab initio calculations and dc magnetic studies, have been performed to confirm a large magnetic anisotropy. A detailed single crystal X-ray diffraction investigation on complex 9 exposed unusual coordination switching from a 5- to 7-coordinate complex, an effect that was turned off when increasing the size of the central ion or steric bulk of the axial ligand. Dynamic magnetic susceptibility studies on complexes 8 - 12 additionally revealed the observation of slow relaxation of magnetisation originating from easy-plane magnetic anisotropy. Three mononuclear Ni(II) complexes were synthesised and characterised as part of this thesis - [NiCl3(DABCO)(HDABCO)] (13), [NiCl3(H2O)(MDABCO)] (14), and [NiCl3(MDABCO)] (15). Enhanced magnetic anisotropy has been evidenced for complex 13 reaching a new record axial ZFS parameter D, as confirmed using cantilever torque magnetometry (CTM) and supported by ab initio calculations. Complexes 14 and 15 were found to exhibit interesting solvatochromic transition between the two isolated complexes, highlighting the potential for multi-functional properties of mononuclear 3d transition metal coordination complexes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Q Science (General) ; QD Chemistry