Synthesis, X-ray crystal structures, and antibacterial activities of Schiff base nickel(II) complexes with similar tetradentate Schiff bases

Two new mononuclear complexes, [NiL1] · CH3OH (I) and [NiL2] (II), have been prepared from the tetradentate Schiff bases N,N'-bis(5-methylsalicylidene)ethylenediamine (H2L1) and N,N'-bis(5-methylsalicylidene)- o-phenylenediamine (H2L2), respectively. The complexes have been characterized by physico-chemical and spectroscopic methods, as well as single-crystal X-ray determination (CIF files nos. 1428969 (I), 1428968 (II)). Complex I crystallizes in the triclinic space group P1 with a = 6.7387(14), b = 10.7010(17), c = 12.681(2) Å, α = 87.059(2)°, β = 88.828(2)°, γ = 89.901(2)°, V = 913.0(3) Å3, Z = 2. Complex II crystallizes in the monoclinic space group P21/n with a = 12.1437(11), b = 8.0537(8), c = 18.4545(18) Å, β = 105.088(2)°, V = 1742.7(3) Å3, Z = 4. The nickel atoms in the complexes are coordinated by two phenolate O and two imine N atoms of the tetradentate Schiff base ligands, forming square planar coordination. The complexes and the Schiff base compounds were assayed for antibacterial activities against three Gram-positive bacterial strains (B. subtilis, S. aureus, and St. faecalis) and three Gram-negative bacterial strains (E. coli, P. aeruginosa, and E. cloacae) by MTT method. As a result, the complexes showed effective antimicrobial activity against the microorganisms tested.