Synthesis, crystal structure, theoretical studies and biological properties of three novel trigonal prismatic Co(II), Ni(II) and Cu(II) macroacyclic Schiff base complexes incorporating piperazine moiety

Abstract

Abstract Trigonal-prismatic structures among different transition metal complexes according to the Cambridge Structural Database (CSD) are rare. The number of trigonal prisms throughout the transition-metal series is less than 1% of all six-coordinate metal centers and only 0.4% of cobalt complexes. Herein we report a novel macroacyclic Schiff base complexes incorporating piperazine moiety with Trigonal-Prismatic coordination were prepared via the metal templated of the 2,2′-(piperazine-1,4-diylbis(methylene))dianiline (A) and 2-formylpyridinein the presence of appropriate Co(II), Ni(II) and Cu(II) metal ions in methanolic/ethanolic solution. The complexes were characterized by elemental analysis, mass spectrometry and FT-IR. Also, the crystal structure of [CoL](ClO4)2·(H2O) complex was obtained by single-crystal X-ray crystallography. An interesting point in this report is the trigonal prismatic coordination for complexes that is the first for Schiff-base complexes containing piperazine moiety. Furthermore, these newly synthesized complexes were evaluated for their in vitro antioxidant and antibacterial activities by using scavenging effects on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and disc diffusion methods, respectively. Based on the resulting experimental data, these compounds exhibited good biological activities. The geometry of [ML]2+ (M = Co, Ni, Cu) complexes have been also optimized at the BP86/def2-SVP level of theory. Furthermore the nature of M ← L (M = Co, Ni, Cu) bonds in the complexes have been studied with the help of NBO and Energy decomposition analysis (EDA). Results showed that the nature of metal-ligand bonds is more covalent (orbital term) with a contribution of about 53.4–62.8% in total interaction energy.