Synthesis, characterization and bioactivity of four novel trinuclear copper(II) and nickel(II) complexes with pentadentate ligands derived from N-acylsalicylhydrazide

Abstract

Four novel trinuclear copper(II)/nickel(II) complexes with four trianionic pentadentate ligands, N-(3- t-butylbenzoyl)-5-nitrosalicylhydrazide (H 33- t-bbznshz), N-(3,5-dimethylbenzoyl)salicylhydrazide (H 33,5-dmbzshz), N-(phenylacetyl)-5-bromosalicylhydrazide (H 3pabshz) and N-(3- t-butylbenzoyl)salicylhydrazide (H 33- t-bbzshz) have been synthesized and characterized by X-ray crystallography. These trinuclear compounds all have an M–N–N–M–N–N–M core formed by three metal ions and two ligands. The geometries of three Cu(II) ions in compound Cu 3(3- t-bbznshz) 2(H 2O)(DMF)(py) 2 · DMF ( 1) alternate between distorted square pyramidal and square planar, while in compound Cu 3(3,5-dmbzshz) 2(py) 2 ( 2), they are all square planar. Three Ni(II) ions in compound Ni 3(pabshz) 2(DMF) 2(py) 2 ( 3) and Ni 3(3- t-bbzshz) 2(py) 4 · 2H 2O ( 4) follow square-planar/octahedral/square-planar coordination geometry. Compounds 1, 2 and 4 are bent trinuclear, with the bend angles of 156.4°, 141.49° and 127.1°, respectively, while the three nickel ions in compound 3 are strictly linear, with an angle of 180°. Studies on the trinuclear Ni(II) complexes show that the β-branched N-acylsalicylhydrazide ligands with sterically flexible Cα methylene groups are easier to yield linear trinuclear Ni(II) complexes, while α-branched N-acylsalicylhydrazides ligands tend to form bent trinuclear Ni(II) complexes. Antibacterial screening data indicate that the trinuclear Cu(II) compound 2 is more active than 1 and mononuclear Cu(II) compound, bent trinuclear Ni(II) compound 4 is more active than linear compound 3 and less active than tetranuclear nickel compound in the previous study.