Synthesis and Characterization of Bis[(RorS)-N-1-(X-C6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]-Λ/Δ-cobalt(II) (X = H,p-CH3O,p-Br) with Symmetry- And Distance-Dependent Vibrational Circular Dichroism Enhancement and Sign Inversion

The enantiopure Schiff bases (RorS)-N-1-(X-C6H4)ethyl-2-hydroxy-1-naphthaldimine {X = H [(RorS)-HL1],p-CH3O [(RorS)-HL2], andp-Br [(R- orS)-HL3]} react with cobalt(II) acetate to give bis[(RorS)-N-1-(X-C6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]-Λ/Δ-cobalt(II) {X = H [Λ/Δ-Co-(RorS)-L1],p-CH3O [Λ/Δ-Co-(RorS)-L2], andp-Br [Λ/Δ-Co-(RorS)-L3]} ( 1 - 3 ), respectively. Induced Λ and Δ chirality originates at the metal center of theC2-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 1 and 3 but irreversible phase transformation for 2 . Like other cobalt(II) complexes, compounds 1 - 3 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 Co2+-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 theAorBsymmetry (in theC2point group) and distance from the Co2+core.