Two highly unsymmetrical tetradentate (N 3O) Schiff base copper(II) complexes: Template synthesis, structural characterization, magnetic and computational studies

Abstract

Two new copper(II) complexes, [Cu 2(L 1) 2](ClO 4) 2 ( 1) and [Cu(L 2)(ClO 4)] ( 2), of the highly unsymmetrical tetradentate (N 3O) Schiff base ligands HL 1 and HL 2 (where HL 1 = N-(2-hydroxyacetophenone)-bis-3-aminopropylamine and HL 2 = N-(salicyldehydine)-bis-3-aminopropylamine) have been synthesised using a template method. Their single crystal X-ray structures show that in complex 1 two independent copper(II) centers are doubly bridged through phenoxo-O atoms (O1A and O1B) of the two ligands and each copper atom is five-coordinated with a distorted square pyramidal geometry. The asymmetric unit of complex 2 consists of two crystallographically independent N-(salicylidene)-bis(aminopropyl)amine-copper(II) molecules, A and B, with similar square pyramidal geometries. Cryomagnetic susceptibility measurements (5–300 K) on complex 1 reveal a distinct antiferromagnetic interaction with J = −23.6 cm −1, which is substantiated by a DFT calculation ( J = −27.6 cm −1) using the B3LYP functional. Complex 1, immobilized over highly ordered hexagonal mesoporous silica, shows moderate catalytic activity for the epoxidation of cyclohexene and styrene in the presence of TBHP as an oxidant.