LAUSR

Abstract 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 against fungi.