Non-covalent interactions governing the supramolecular assembly of copper(II) complexes with hydrazone-type ligand: Experimental and quantum chemical study

A series of two new mono- and one binuclear m-nitrato bridged copper(II) complexes [Cu(L)(HL)]ClO4 (1), [Cu(HL)(NO3)(H2O)](2)NO3 center dot H2O (2) and [Cu-2(L-2)(mu-NO3)(2)] (3), with an unsymmetrical NNO donor Schiff base (HL) have been synthesized and characterized by elemental analysis, FTIR, CV, UV-vis and EPR spectroscopy. Their molecular structures were also determined by single crystal X-ray crystallography. In the binuclear complex 3, the Cu center dot center dot center dot Cu distance is 3.494 angstrom. In 1, 2 and 3, the Cu(II) centers have distorted square pyramidal geometry (tau(5) = 0.05-0.17). Evidence of weak pi center dot center dot center dot pi stacking intermolecular interactions along with other non-covalent interactions (hydrogen bonding) was observed by analyzing the respective crystal structures of the complexes. Thus, these hydrogen bonds, pi center dot center dot center dot pi stacking interactions and other weak intermolecular interactions establish in the form of supramolecular architectures a crystalline "network" environment. The non-covalent interactions were also investigated by employing Hirshfeld Analysis. The room temperature magnetic moments of the mononuclear complexes are less than the spin only values which are indicative of small interactions. Also, significant magnetic interactions were not exhibited by binuclear copper(II) complex 3 in the variable temperature magnetic measurements. The X-band EPR spectra of all three complexes exhibit copper(II) hyperfine structures as well as zero-field splitting which are appropriate for the triplet states of dimers. In complexes 1 and 2, the presence of pseudo dipolar interactions is proposed. Quantum chemical calculations (DFT) were carried out on complexes 1-3 to explore the electronic and spectral properties of these newly synthesized complexes. These complexes show significant antiproliferative and SOD activity. The SOD activity measured in terms of kMcCF is in the range 4.94-12.31 (mol L)(-1)s(-1))x 10(4). (C) 2021 Elsevier Ltd. All rights reserved.