Iron complexes with triazole-based ligand: extend the SCO molecule to high dimensional materials

The major focus of this thesis involves preparation of new Fe(II) complexes with potential to exhibit SCO transition. In order to acquire and tune SCO properties, a series of novel triazole-based ligands (L1 to L17), as well as their Fe(II) complexes were synthesized and characterized. Special attention was given to construct high diemsional Fe(II) complex with possible spin switching properties. Ligands can mainly be divided into two different groups based on their flexibility. The first group of ligands shares an urea group between the triazole ring and the functional groups (L1 to L8), which can be treated as flexible ligands; the second group of ligands is built up from triazole Schiff base, with a Schiff base bond as linkage (L10 to L16), which can be assigned to half-rigid ligands. Besides these two groups, a reported ligand 4-(p-carboxyphenyl)-1,2,4-triazole (L9) and a newly synthesized ligand 3,3’,5,5’-tetra[(2-pyridylmethyl)amino-methyl]-4,4’-azo-1,2,4-triazole (L17) are also prepared for the present stuty. A number of novel complexes have been synthesised and characterized with these ligands, some of which exhibit interesting magnetic behaviours ranging from SCO transitions to antiferromagnetic coupling to ferromagnetic coupling. A series of three dinuclear and two trinuclear N1,N2-triazole bridged Fe(II) complexes are summarized in Chapter 2 and Chapter 3, which covered the discussion of SCO transitions and antiferromagnetic coupling among these five discrete molecular complexes. Chapter 4 contained three polyuclear Fe complexes with the coordination mediated by a second carboxyl-based ligand (oxalate, citrate). The three structures differed from a Fe(III) dimer to a Fe(II) one dimensional chain to a Fe(II) three dimensional framework. Detailed magnetic properties of these three complexes are explored. The high dimensional networks built up from the [FeN6] core are summarized in Chapter 5, which covers two examples of 2D Fe(II) layered networks with quite different magnetic behavior: one complex shows ferromagnetic coupling between the linked Fe(II) centers, while the second one exhibits weak antifemagnetic coupling through the supramolecular interactions. Beyond the successful synthesis and characterization of these desired complexes, Chapter 6 summarizes several crystal structures that formed as unexpect results during the present study. These structures mainly came out as a result of the competition between the crystallization of the targeted complex and the isolated by-product, either Fe complex or pure ligand form. Detailed discussion has been made in regard to explore the relationship between the supramolecular interactions and the unexpected crystals formation