Bis-pyrazolyl-s-triazine Ni(II) pincer complexes as selective gram positive antibacterial agents; synthesis, structural and antimicrobial studies

A new heteroleptic octahedral [NiL(H2O)(3)](NO3)(2)center dot 1/2H(2)O complex with the tridentate pincer type ligand L; 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine, was synthesized and characterized using self assembly and single crystal X-ray diffraction, respectively. The Ni(II) ion is coordinated with one organic ligand unit (L) as NNN-chelate and three water molecules in the inner sphere while the outer sphere contains two nitrate anions and half crystal water molecule. The nitrate ions and the crystal water molecule connected the complex cation units via O-H center dot center dot center dot O hydrogen bonding interactions. Also, the nitrate ions are effectively interacting with the coordinated organic ligand via anion-pi stacking interactions. The percentages of the O center dot center dot center dot H contacts range from 34.5 to 37.7% using Hirshfeld analysis. As a result of the interaction between the Ni(II) and ligand groups, its charge and spin densities were reduced to 0.86 and 1.68 e, respectively instead of 2.00 e. The nature and strength of the Ni-O and Ni-N coordination interactions were discussed using atoms in molecules theory. The Ni-N(triazine) and the equatorial Ni-O bonds showed the highest interaction energies among the Ni-N and Ni-O bonds, respectively. Antimicrobial studies on selected Ni(II) pincer complexes of L indicated high selectivity against the Gram positive bacteria with very close actions to the positive control Gentamycin. The organic ligand showed no antimicrobial action at the applicable concentration. (C) 2019 Elsevier B.V. All rights reserved.