Neutral self-assembly of dinuclear copper(ii) metallacycles derived from Schiff base ligands: synthesis, characterization and catalysis

Abstract

Metallacycles are structurally diverse molecular entities that have attracted significant research interest due to their potential applications in sensing, catalysis, and biomedicine. In this study, we report the synthesis of two discrete neutral Schiff base-derived dinuclear Cu(II) metallacycles [Cu₂L₂] (1) and [Cu₂L′₂] (2) achieved through coordination driven self-assembly using ligands N,N′-bis(3,5-di-tert-butylsalicylidene)-2,2′-diaminodiphenyl ether (H₂L) and (N,N′-bis(3,5-di-tert-butylsalicylidene)-hydrazine) (H₂L′), respectively. 1 and 2 are characterized by infrared, UV-vis, fluorescence, and electron paramagnetic resonance spectroscopy. The X-ray diffraction analysis confirms that 1 adopts a double helical structure while 2 exhibits a butterfly shape. The magnetic and electrochemical properties of metallacycles are investigated using superconducting quantum interference device (SQUID) magnetometry and cyclic voltammetry. The results revealed that the macrostructure of the metallacycles significantly influences their photophysical, magnetic and electronic properties. In addition, the catalytic efficiency of metallacycles towards ring-opening polymerization of ε-caprolactone is evaluated.