Binuclear transition metal complexes of a novel lateral N-methylthiosemicarbazone through the central ethylene bridge: Synthesis, structural characterization and the response of ligand molecule to different solvent media

The condensation of 2,2′-(2,3-bis((1-formylnaphthalen-2-yloxy)methyl)but-2-ene-1,4-diyl)bis(oxy)di-1-naphthaldehyde with 4-methyl thiosemicarbazide gave a novel N-methylthiosemicarbazone and then the reaction of this compound with M(ClO4)2·6H2O, Cu(II), Ni(II) and Zn(II), in dry EtOH, gave homobinuclear transition metal complexes of 21-membered tetraoxatwelveazatetrathia macrocycle. The structure of ligand and the mode of bonding and overall geometry of the complexes have been inferred through UV–vis, IR, 1H/13C NMR, mass, elemental analyses, spectral techniques as well as molar conductivities and magnetic moment data. The molar conductance data reveal that Cu(II), Ni(II) and Zn(II) chelates are ionic in nature and are of the type 4:1 electrolytes. In Cu(II) and Ni(II) complexes, the environmental effect around the metal ion is in square–planar N2S2 coordination geometry and in Zn(II) complex, is tetrahedral geometry. According to these data, the ligand is found to be chelated to the metal(II) center in its thiolate form through its imine nitrogen and the thiolate sulfur. Additionally, electronic structures of all complexes 4–6, which we just synthesized, have been studied by DFT level (6-31G(d,p)/B3LYP/Lanl2dz) calculations. NBO charge distribution and the characteristics of frontier molecular orbitals of these complexes are also investigated. Furthermore, the experimental description related with calculations is given in experimental section.