Non-covalent interactions in molecular architectures and solvent-free catalytic activity towards CO2 fixation of mononuclear Co(iii) complexes installed on modified Schiff base ligands

Abstract

A set of mononuclear cobalt(III) octahedral complexes {[Co(L^H)(acac)] (Co-1^H), [Co(L^Br)(acac)] (Co-1^Br), and [Co(L^NO2)(acac)] (Co-1^NO2)} were synthesized using new-generation N/O donors, maleonitrile-tethered, tetradentate heteroscorpionate half-reduced Schiff base ligands, 2-((E)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H₂L^H), 2-((E)-(5-bromo-2-hydroxybenzylidene)amino)-3-((pyridin-2-ylmethyl)amino)maleonitrile (H₂L^Br), and 2-((E)-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H₂L^NO2). All the compounds were well characterized spectroscopically and structurally. The non-covalent interactions present in the lattice of Co-complexes were studied in detail to explain the molecular architecture using the Hirshfeld surface (HS) analysis. The catalytic activity of CO₂ fixation towards epoxides under mild and solvent-free conditions was demonstrated. The synthesized complexes are catalysts that are well-active towards the CO₂ activation under ambient conditions, whereas most of the reported catalysts require harsh conditions.