Electrocatalytic reduction of carbon dioxide induced by bis( N-R-2-hydroxy-1-naphthaldiminato)-copper(II) (R = n-octyl, n-dodecyl): Magnetic and theoretical studies and the X-ray structure of bis( N- n-octyl-2-hydroxy-1-naphthaldiminato)-copper(II)

Abstract

Copper(II) complexes of n-alkyl-2-hydroxy-1-naphthaldimine Schiff bases (with n-alkyl: n-octyl, and n-dodecyl) have been synthesized, to study steric and electronic effects of long alkyl chain substituents on their structure and properties. These complexes have been characterized with FT-IR, UV–Vis, magnetic susceptibility and cyclic voltammetry both in nitrogen and carbon dioxide atmosphere. Metal-ligand coordination is inferred from the shifting of the ν C N stretching vibration mode in the 1610–1620 cm −1 region when compared to that of the free ligand. The UV–Vis spectra show one band around 640 nm typical for square planar Cu(II) complexes. Results obtained from cyclic voltammetry indicate electrocatalytic reduction of carbon dioxide around −0.90 V (versus Ag/AgCl). Bis( N- n-octyl-2-hydroxy-1-naphthaldiminato)-copper(II) has been studied with X-ray diffraction. The molecular structure shows the copper atom in a planar environment and the n-octyl chains having thermal disorder. The crystal packing shows stacked units intermolecularly separated by 3.33 Å, probably due to π–π interactions between naphthyl groups, and Cu–O and O–O separations of 3.95 and 3.42 Å, respectively. The magnetic susceptibility data between 10 and 300 K are indicative of diluted paramagnetic behavior. Density functional theory calculations of spin density for the n-octyl complex shows the unpaired electron localized along the planar CuO 2N 2 moiety. The calculated electrostatic potential show electron rich regions on the oxygen atoms.