Syntheses, crystal structures, and antibacterial activities of four schiff base complexes of copper and zinc

Abstract

Four Schiff base complexes, [Cu2(L1)2(μ-NCS) 2] (1), [Cu2(L2)2(μ-N3) 2] (2), Cu[Cu(CH3COO)(L3)]2 (3), and [Zn {Zn(C3H4N2)(L3)}2(NO 3)](NO3) (4) (where L1 = 2-[(pyridin-2-ylmethylimino) methyl]phenol, L2 = 1-[(pyridin-2-ylmethylimino)methyl]naphthalen-2-ol, and L3 = bis(salicylidene)-1,3-propanediamine), were synthesized and characterized by elemental analyses, infrared spectroscopy, and single crystal X-ray determinations. Both 1 and 2 are structurally similar di-nuclear complexes, which are located at crystallographic inversion centers (with the center of the central Cu2N2 ring). In 1, each copper atom has a slightly distorted square pyramidal configuration, coordinated by two nitrogen atoms and one oxygen atom from L1 and another two terminal nitrogen atoms from two bridging thiocyanate anions. The Cu⋯Cu separation is 3.466(3) Å. The structure of 2 is similar to that of 1, with Cu⋯Cu separation of 3.368(2) Å. Both 3 and 4 are linear tri-nuclear complexes. In 3, the central Cu2+ ion is located on an inversion centre and has a distorted octahedral coordination involving four bridging O atoms from two Schiff base ligands (L3) in the equatorial plane and one O atom from each bridging acetate group in the axial positions. The coordination around the terminal Cu2+ ions is irregular-square pyramidal, with two O and two N atoms of L3 in the basal plane and one O atom from an acetate group in the apical position. The acetate bridges linking the central and terminal Cu 2+ ions are mutually trans. The Cu⋯Cu separation is 3.009(3) Å. In 4, the coordination configuration of the central and the terminal zinc atoms are similar to that of the 3, with Zn⋯Zn separation of 3.153(4) Å. The three Schiff bases and the corresponding three copper complexes exhibit good antibacterial properties, while the zinc complex 4 has nearly no.