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Transition metal fragments displaying switching behaviour are appealing materials, which may be used in a functional way in research and technology. Some molecular species containing transitionmetal ions may exhibit a crossover between states having a different magnetic moment, the magnetic interconversion between the low-spin and high-spin state in FeIII systems which can be triggered by a change in temperature, pressure or by light irradiation. The research presented in this thesis focuses on using substituted derivatives of R-salicylaldehyde 4R’-thiosemicarbazone (H2L, H2-R-thsa-R’) for generating FeIII spin crossover. The aim was to design mononuclear FeIII compounds with a view of studying their structural features and magnetic properties. The results present the full structural analysis of differently charged FeIII-bis(ligand) complexes, these include: (i) (cation+)[FeIII(L2‒)2]·x(solvent), (ii) [FeIII(HL‒)(L2‒)]·x(solvent) and(iii) [FeIII(HL‒)2](anion‒)·x(solvent). The studies discuss several influences on the structural features and the magnetic properties of the reported FeIII compounds, these include: the nature of the anionor cation associated with the FeIII complex, the degree of solvation of the complex and the variations in the ligand substituents. The magnetic studies of the (cation+)[FeIII(L2‒)2]·x(solvent) compounds have presented one high-spin compound ((CH3)2NH2[Fe(3-OEt-thsa)2]) and four low-spin compounds (Cs[Fe(3-OEt-thsa-Me)2]·CH3OH, Cs[Fe(5-Br-thsa)2], NH4[Fe(thsa)2] and NH4[Fe(5-Br-thsa)2]), of which NH4[Fe(5-Br-thsa)2] revealed a fraction of the FeIII ions convert into the high-spin state. Three [FeIII(HL‒)(L2‒)]·x(solvent) compounds have been studied, of which a rare two-step spin transition has been observed for [Fe(H-5-Cl-thsa-Me)(5-Cl-thsa-Me)]·H2O, while the isostructural compounds [Fe(Hthsa-Me)(thsa-Me)]·H2O undergoes an incomplete spin transition and [Fe(H-3-OEt-thsa-Me)(3-OEt-thsa-Me)]·H2O remains in the high-spin state. It was recognised that the steric and electronic features imposed by the R,R’-substituents may have an impact on the spin state of FeIII cations, and affect at which temperature the spin transition occurs. Furthermore, the FeIII cation of both [FeIII(HL‒)2](anion‒)·x(solvent) compounds, [Fe(H-5-Br-thsa-Et)2](NO3)·H2O and [Fe(H-4-OHthsa)2]4·(SO4)2·9H2O, were found to be in the high-spin state. Collectively, the described research has provided new insight into this family of FeIII bis(Rsalicylaldehyde4R’-thiosemicarbazone) compounds and provides a strong foundation for further studies. |
