Synthesis, structure and bioactivity of Ni2+ and Cu2+ acyl­hydrazone complexes

Two acyl­hydrazone complexes, bis{6-methyl-N′-[1-(pyrazin-2-yl-κN1)ethyl­idene]nicotinohydrazidato-κ2N′,O}nickel(II), [Ni(C13H12N5O)2], (I), and di-μ-azido-κ4N1:N1-bis­({6-methyl-N′-[1-(pyrazin-2-yl-κN1)ethyl­idene]nicotinohydrazidato-κ2N′,O}nickel(II)), [Cu2(C13H12N5O)2(N3)2], (II), derived from 6-methyl-N′-[1-(pyrazin-2-yl)ethyl­idene]nicotinohydrazide (HL) and azide salts, have been synthesized. HL acts as an N,N′,O-tridentate ligand in both complexes. Complex (I) crystallizes in the ortho­rhom­bic space group Pbcn and has a mononuclear structure, the azide co-ligand is not involved in crystallization and the Ni2+ centre lies in a distorted {N4O2} octa­hedral coordination environment. Complex (II) crystallizes in the triclinic space group P\overline{1} and is a centrosymmetric binuclear complex with a crystallographically independent Cu2+ centre coordinating to three donor atoms from the deprotonated L− ligand and to two N atoms belonging to two bridging azide anions. The two- and one-dimensional supra­molecular structures are constructed by hydrogen-bonding inter­actions in (I) and (II), respectively. The in vitro urease inhibitory evaluation revealed that complex (II) showed a better inhibitory activity, with the IC50 value being 1.32±0.4 µM. Both complexes can effectively bind to bovine serum albumin (BSA) by 1:1 binding, which was assessed via tryptophan emission–quenching measurements. The bioactivities of the two complexes towards jack bean urease were also studied by mol­ecular docking. The effects of the metal ions and the coordination environments in the two complexes on in vitro urease inhibitory activity are preliminarily discussed.