Synthesis and Characterization of Bis[( or )--1-(X-CH)ethyl-2-oxo-1-naphthaldiminato-κ,]-Λ/Δ-cobalt(II) (X = H, -CHO, -Br) with Symmetry- and Distance-Dependent Vibrational Circular Dichroism Enhancement and Sign Inversion.

The enantiopure Schiff bases ( or )--1-(X-CH)ethyl-2-hydroxy-1-naphthaldimine {X = H [( or )-HL1], -CHO [( or )-HL2], and -Br [(- or )-HL3]} react with cobalt(II) acetate to give bis[( or )--1-(X-CH)ethyl-2-oxo-1-naphthaldiminato-κ,]-Λ/Δ-cobalt(II) {X = H [Λ/Δ-Co-( or )-L1], -CHO [Λ/Δ-Co-( or )-L2], and -Br [Λ/Δ-Co-( or )-L3]} (-), respectively. Induced Λ and Δ chirality originates at the metal center of the -symmetric molecule in pseudotetrahedral geometry. Differential scanning calorimetry analyses explored the thermal stability of the complexes, which undergo reversible phase transformation from crystalline solid to isotropic liquid phase for and but irreversible phase transformation for . Like other cobalt(II) complexes, compounds - exhibit a continuous ensemble of absorption and circular dichroism bands, which span from the UV to IR region and can be collected into a superspectrum. Infrared vibrational circular dichroism (IR-VCD) spectra witness the coupling between Co-centered low-lying electronic states and ligand-centered vibrations. The coupling produces enhanced and almost monosignate VCD spectra, with both effects being mode-dependent in terms of the or symmetry (in the point group) and distance from the Co core.