Chirality Transfer in Magnetic Coordination Complexes Monitored by Vibrational and Electronic Circular Dichroism

Magnetic coordination complexes based on Schiff bases are promising new molecular materials for electronics. Two -oxo Fe-III dimeric complexes of enantiomers of Schiff base ligands (N,N-(1R,2R)-1,2-diphenylethylenebis(salicylideneimine) (H(2)salphen-R, 1a) and N,N-(1S,2S)-1,2-diphenylethylenebis(salicylideneimine) (H(2)salphen-S, 1b)) were synthesized; further reaction with 4-salicylideneamino-1,2,4-triazole (Hsaltrz) led to enantiomers of two one-dimensional (1D) Fe-III coordination complexes. The structures of these complexes were determined by X-ray diffraction. Magnetic susceptibility measurements revealed that -oxo dimeric complexes displayed strong antiferromagnetic coupling, whereas the 1D complexes exhibited paramagnetic behavior. The chirality of the Schiff bases transferred to macromolecular chirality of the complexes, which could be monitored by both vibrational and electronic circular dichroism (CD) spectroscopic methods. The macroscopic handedness was manifested in CD signals attributed to exciton coupling between the ligands. Thus, the chiral spectroscopies were useful to probe the chirality of the complexes, their structure, and the polymerization degree.