Copper(II) benzoates (nOBA-Cu) with various terminal alkoxy carbon numbers, n=7-12, were prepared from p-n-alkoxy benzoic acids (nOBAs). Fourier transform infrared (IR) experiments suggested that dimerization through copper(II) chelating bidentate coordination created nOBA-Cu with a linear rod-like structure, similar to the hydrogen-bonded structure of its parent nOBA. However, the coordination structure of nOBA-Cu changed during heating. Periodic density functional theory calculations provided valuable insight into the possible arrangement of the parent and copper(II)-coordinated nOBAs. The formation of binuclear complexes between two adjacent nOBA-Cu dimers forced nOBA-Cu to arrange itself in a layer and exhibit smectic A mesophase. Accordingly, four types of IR stretching absorption of benzoyl carbonyl were observed in binuclear nOBA-Cu complexes, replacing the original symmetric and asymmetric vibrations of benzoyl carboxylate in chelating bidentate coordination. The lateral association by π-π interactions between adjacent parent nOBA dimers preferred a progressive smectic C arrangement. The origin of the odd-even effect was understood from the consideration of the molecular structure.
?Journal of Theoretical and Computational Chemistry 18(01) · January 2019