Observation of an anion•••anion interaction in a square planar copper(II) Schiff base complex: DFT study and CSD analysis

A centrosymmetric square planar bis-ligand copper(II) complex, [Cu(HL)(2)](CIO4)(2), with a potential tetradentate Schiff base, HL = 2-(2-(ethylamino)ethyliminomethyl)-6-ethoxyphenol, containing pendant side arm, has been prepared and characterized by elemental and spectral analysis and single crystal X-ray diffraction studies. The potential tetradentate Schiff base is trapped in its zwitterionic form and shows a bidentate bonding mode. Several weak forces like hydrogen bonding and C-H center dot center dot center dot pi interactions lead to the formation of supra-molecular architecture. The existence of an anion-anion interaction between the perchlorate anions have been analyzed using DFT calculations, the Bader's theory of atoms-in-molecules (AIM) and the non-covalent interaction index (NCI plot). The O center dot center dot center dot O distance is 2.848(2) angstrom.