Template synthesis, structural variation, thermal behavior and antimicrobial screening of Mn(II), Co(II) and Ni(II) complexes of Schiff base ligands derived from benzyl carbazate and three isomers of acetylpyridine

• Published in: Inorganica Chimica Acta 2017-10, Vol.467, p.180-193
• Main Authors: Nithya, Palanivelu, Simpson, Jim, Govindarajan, Subbiah
• Format: Article
• Language: English
• Subjects: Antiinfectives and antibacterials; Antimicrobial agents; Antimicrobial properties; Benzyl carbazate; Cations; Chelates; Chemical synthesis; Condensates; Coordination compounds; Copper; Crystal structure; Differential thermal analysis; Imines; Infrared radiation; Isomers; Isomers of acetylpyridine; Ligands; Manganese; Manganese compounds; Molecular chains; Nickel; NMR; Nuclear magnetic resonance; Screening; Single crystals; Six-coordinate metal complexes; Thermal behavior; Thermodynamic properties; X-ray crystal structures
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2017.07.059

Eight new coordination complexes based on benzyl carbazate and three stereoisomers of acetylpyridine have been synthesized by template method. Thermal reactivity of the complexes was studied by TG-DTA. All of them, except 1, have significant activity against both Gram-positive and Gram-negative bacterial strains and also against fungi. [Display omitted] •Synthesis of metal complexes of Schiff bases from benzyl carbazate and acetylpyridines.•Characterization of the compounds by analytical and spectroscopic techniques.•Crystal Structures of the compounds show octahedral coordination.•Thermal behaviour of the complexes has been explored.•Antimicrobial screening of metal complexes carried out with bacteria and fungi. Complexes of Mn(II), Co(II) and Ni(II) with ligands derived from the condensation of benzyl carbazate with three stereoisomers of acetylpyridine have been synthesized using a template method. The complexes have the compositions [Ni(bc-2ap)2] (1), [M(NCS)2(bc-3ap)2(bc)]·H2O; M=Co (2) or Ni (3), [Mn(NCS)2(bc-3ap)4]·2CH3OH (4), [M(NCS)2(bc-3ap)4]·2H2O; M=Co (5) or Ni (6) and [M(NCS)2(bc-4ap)2(CH3OH)2]; M=Mn (7) or Co (8) [where bc=benzyl carbazate, 2ap, 3ap and 4ap=2-, 3- and 4-acetylpyridine]. Characterization of the products involved elemental analysis, IR, UV–vis and 1H NMR, and in the case of 1, 2, 4, 5 and 8 single crystal X-ray structures have been determined. These are all six coordinate with octahedral coordination geometries. Compound 1 is unique with the 2-acetylpyridine ligand undergoing enolisation and deprotonation with two of the uninegative ligands coordinating to the Ni(II) cation in a tridentate chelate fashion. For 2 to 8 the charges of the M(II) cations are balanced in each case by two thiocyanato ligands, mutually cis for 2 and 3 but trans for 4–8. In these latter six-coordinate complexes, 2–8, the benzyl carbazate derived Schiff base ligands bind to the metal atoms in a trans monodentate fashion via the pyridine N atoms, two for 2, 3, 7 and 8 and four such ligands for 4, 5 and 6. In addition to the thiocyanato anions, the remaining coordination positions are filled by bidentate chelate carbazate molecules for 2 and 3, and two trans oriented methanol molecules for 7 and 8. Thermal reactivity of the complexes was studied by TG-DTA. In addition, antimicrobial screening confirmed that all of the complexes, except 1, have a moderate to good range of activity against both Gram-positive and Gram-negative bacterial strains and also again