Synthesis of copper(ii) complex-functionalized Fe3O4@ISNA (ISNA = isonicotinic acid) as a magnetically recoverable nanomaterial: catalytic studies in alcohol oxidation and nitrophenol reduction, and TD-DFT studies

Abstract

Two newly designed ligands, [4-chloro-2-((((2-pyridyl)ethyl)imino)methyl)phenol] (HL¹) and [4-bromo-2-((((2-pyridyl)ethyl)imino)methyl)phenol] (HL²), have been chosen to synthesize two Cu(II) dimeric Schiff base complexes, [CuL¹Cl]₂ (1) and [CuL²Cl]₂ (2), with the aim of studying their catalytic activity towards oxidation of alcohols by using H₂O₂ as a terminal oxidant and reduction of nitroarenes by using NaBH₄ as a reducing agent. The complexes have been characterized using physicochemical techniques and single crystal X-ray diffraction. DFT calculations of both the complexes have also been performed. Complex [CuL¹Cl]₂ (1) exhibited a higher catalytic efficiency in each reaction and therefore it was selected for building a magnetically separable catalyst by attaching it to surface modified magnetic nanoparticles. Then, our goal was to modify further complex 1 with iron oxide and isonicotinic acid (ISNA), for easy magnetic separation. The new Fe₃O₄@ISNA@CuL¹ catalyst underwent comprehensive characterization, including FT-IR, SEM, TEM, and PXRD analyses, confirming successful copper complex immobilization on the magnetic nanoparticles. These catalysts maintained stability in aqueous and organic media, enabling alcohol oxidation with H₂O₂ in acetonitrile and nitroarene reduction with sodium borohydride in an aqueous environment. The surface modification with magnetic nanoparticles facilitated easy separation using an external magnet. The novelty of this work lies in its straightforward preparation, minimal time consumption, reduced use of hazardous chemicals, and cost-effectiveness. The catalysts showed recyclability up to five times without significant loss of activity. Furthermore, our synthesized catalysts demonstrated non-toxicity and environmental friendliness.