| The interest in magnetic bistable systems has grown significantly in recent years because of the potential applications in information storage, molecular switches, molecular electronics, and optical devices. In particular, chiral magnetic bistable complexes become current social hot research because they may offer wide new perspectives, for instance, in magneto-chiral dichroism, and ferroelectricity. This thesis is aimed at designing and synthesizing of a seris of homochiral mononuclear and tetranuclear complexes, and controlling magnetic bistable properties of complexes through changing the strength of ligands. This thesis includes three parts:(1) Eight novel homochiral mononuclear spin-crossover iron(II) complexes 1-8: fac/mer-Λ/Δ-[Fe(Ln)3][ClO4]2(n = 1-8,Ln represent different chiral imidazole schiff-base ligands) have been designed and successfully synthesized. These complexes have been determined by single-crystal X-ray diffraction analysis, elemental analysis, IR spectra, CD spectra, and magnetic measurements. X-ray crystallography revealed that the iron(II) center in 1-8 assumed an octahedral coordination environment with six N donor atoms from three unsymmetrical bidentate chiral schiff-base ligands. Each unit contained one [Fe(Ln)3]2+ cation and two ClO4? anions for all complexes. [Fe(Ln)3]2? components were chiral with either Λ or Δ configuration due to the screw coordination arrangement of the chiral ligand around Fe(II) centers. The Fe(II)-N bond distances at 173 K indicated that the Fe(II) sites of 5 and 7 were in high-spin state, while the Fe(II) centers of 1-4, 6 and 8 were in low-spin state. As for [Fe(Ln)3]2+, intramolecular π-π interactions were present between phenyl group and imidazole ring of an adjacent ligand. In 1-8, various supramolecular architectures were formed through intermolecular C-H???π and/or C-Cl???π interactions. Circular dichromism spectra confirmed the presence of non-racemic chiral metal centers in solution for complexes 1-8. Magnetic measurements revealed that 1-8 displayed obviously bistable behaviour at 232, 250, 257, 372, 146, 375, 137 and 282 K, respectively. Analysis revealed that the different SCO bahaviors of 1-8 may result from substitution effect, packing mode, and intermolecular interactions.(2) Three pairs of chiral enantiopure tetrahedral cages 9-11([Fe4L6](ClO4)8·solvent(L = 1,4-di((imidazol-2-ylmethylene)-1-phenylethanamine)butane derivatives)) were prepared from subcomponent self-assembly of 1,4-di(imidazole-2-carboxaldehyde)butane, chiral phenylethylamine and iron(II) ions. These cages have been determined by single-crystal X-ray diffraction analysis, elemental analysis, IR spectra, CD spectra, and magnetic measurements. Cages 9 and 11 crystallized in trigonal R3 chiral space group, while 10 crystallized in triclinic P1 chiral space group. The self-assembly proceeded with high diastereoselectivity and only one single cage diastereomer of either ΔΔΔΔ or ΛΛΛΛ was observed. Circular dichromism spectra confirmed the absolute configuration and enantiopurity in solution for cages 9-11. The cages can be interconvered through imine exchange by taking advantage of the electron density between various phenylethylamine due to dynamic imidazole-imine(C=N) based ligands in cages, which are demonstrated by 1H NMR spectra. Magnetic measurements revealed that 9-11 displayed bistable behaviour close to room temperature, and the transition temperatures were affected by the substituent of the chiral phenylethylamine subcomponents, and uncoordination solvents.(3) In order to study the effect of briging groups between two imidazole-2-carboxaldehyde on magnetism, three novel homochiral spin-crossover iron(II) tetranuclear cages 12-14([Fe4L6](ClO4)8·solvent(L = 1,4-di((imidazol-2-ylmethylene)-1-phenylethanamine)butane derivatives))have been successfully synthesized through changing briging group between two imidazole-2-carboxaldehyde. These complexes have been determined by single-crystal X-ray diffraction analysis, elemental analysis, IR spectra, CD spectra, and magnetic measurements. The self-assembly proceeded with high diastereoselectivity and only one single cage diastereomer of ΔΔΔΔ was observed for 12-14. Circular dichromism spectra confirmed the absolute configuration for 12-14. Magnetic measurements revealed that 12-14 displayed bistable behaviour transition temperatures were affected by the briging groups between two imidazole-2-carboxaldehyde. |
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