Tri-nuclear copper-cadmium complexes of a N2O2-donor ligand with the variation of counter anions: Structural elucidation and theoretical study on inter-molecular interactions

Abstract

Four new tri-nuclear hetero-metallic copper(II)-cadmium(II) complexes [(CuL)2CdCl2] (1), [(CuL)2CdBr2] (2), [(CuL)2CdI2] (3) and [(CuL)2Cd(NO3)2] (4) have been synthesized using [CuL] as ‘‘ligand complex’’ (where H2L = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine) and characterized by elemental analysis, IR, UV–Vis spectroscopy and single crystal X-ray diffraction studies. Crystal structure analyses reveal that all four complexes consist of a tri-nuclear moiety in which two square-pyramidal [CuL] units are bonded to a central Cd(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate octahedral environment being bonded additionally to two mutually trans chloride (in 1), bromide (in 2), iodide (in 3) and oxygen atoms of nitrate (in 4) ions. Presence of several non-covalent interactions (i.e. π···π, Csingle bondH···O and Cu···Cu interactions) has been observed in the crystal packing of all the four molecules that assist the formation of 1D supramolecular assemblies in the solid state. The interactions were investigated by means of high level DFT calculations (PBE0-D3/def2-TZVP) with the help of TURBOMOLE 7.0 program, characterized using Bader’s theory of “atoms-in-molecules” (AIM) and rationalized using molecular electrostatic potential (MEP) surface calculations.