Syntheses, Structures and Magnetic Properties of Homochiral Spin-Crossover Iron(II) Schiff-Base Complexes

Two homochiral mononuclear spin-crossover iron(H) complexes, namely,fac-A-[Fe(R-L-1)(3)](ClO4)(2) (1), facA-[Fe(R-L-2)(3)](ClO4)(2) (2) have been successfully synthesized by subcomponent self-assembly of Fe (ClO4)(2), 4-(imidazole-2-carboxaldehyde)butyronitrile and optical phenylethylamine derivatives. The two complexes have been determined by single-crystal X-ray diffraction analysis, elemental analysis, IR spectra, H-1 NMR spectra, UV spectra and CD spectra. X-ray crystallography revealed that the iron(11) center in 1 and 2 assumed an octahedral coordination environment with six N donor atoms from three unsymmetrical bidentate chiral schiff-base ligands. Each unit contained one [Fe (L)(3)](2+) cation and two ClO4- anions. [Fe(L)(3)](2) components were chiral with A configuration due to the screw coordination arrangement of the chiral ligand around Fe(II) centers. The Fe(II)-N bond distances indicated that the Fe(II) sites of 1 and 2 were in low-spin state. As for [Fe(L)(3)](2+), intramolecular pi-pi interactions were present between phenyl group and imidazole ring of an adjacent ligand. In 1 and 2, 3D supramolecular architectures were formed through intermolecular C-H center dot center dot center dot pi interactions. Circular dichromism spectra confirmed the presence of non-racemic chiral metal centers in solution for complexes 1 and 2. Magnetic measurements revealed that 1 and 2 displayed obviously spin-crossover behaviour at 232 and 250 K, respectively. Complexes 1 and 2 crystallized in the same chiral space group with similar packing modes and intermolecular interactions, therefore their different SCO bahaviors mainly resulted from substitution effect. CCDC: 1020956, 1; 1020957, 2.