New cyclic tetranuclear copper(II) complexes containing quadrilateral cores: Synthesis, structure, spectroscopy and their interactions with DNA in aqueous solution

Three new cyclic tetranuclear copper(II) complexes, Tetrakis(3-[(2-pyridylmethyl)-amino]-propionato)(tetrachloro)tetracopper(II)methanolhydrate (1 center dot CH3OH center dot H2O), Tetrakis{3-[(2-pyridylmethyl)-aminc]propionato)(tetrathiocyanato)tetracopper(II) (2) and Tetrakis(3-[(2-pyridylmethyl)-amino]-propionato)(tetraazido)tetracopper(II) (3) have been synthesized by exploiting the chelating ability and bridging potential of a carboxyamine functionalized tridentate ligand, HL (HL = 3-[(2-Pyridylmethyl)-amino]propionic acid). Complexes 1, 2 and 3 have been synthesized by carrying out reaction of the ligand HL with stoichiometric amounts of CuCl2 center dot 2H(2)O, CuCl2 center dot 2H(2)O/NRISCN, and CuCl2 center dot 2H(2)O/NaN3, respectively, in the presence of NMe4OH at ambient temperature. Various analytical techniques have been employed to characterize the complexes, including single crystal X-ray diffraction study of 1. Structures of complexes 2 and 3 have been optimized by DFT calculation at B3LYP/6-311G level. Analysis of X-ray crystal structure reveals that the metallic core of complex 1 contains four distorted square pyramidal Cu(II) ions. The Cu(II) ions in each complex are arranged at the corners of a quadrilateral showing a mu(2):eta(1):eta(1) syn-anti bidentate bridging mode of four carboxylate groups of L- ligands with each bridging between two Cu(II) ions. These complexes represent a new family of 16-MCCuII-4 metallocoronates with repeating -[Cu-II-O-C-O]- units. In aqueous solution (pH similar to 7.5), the interactions of complexes with DNA have been investigated by UV-Vis and fluorescence titration spectroscopy, and viscosity measurements. (C) 2017 Elsevier B.V. All rights reserved.