Syntheses, structural diversity and thermal behavior of first row transition metal complexes containing potential multidentate ligands based on 2,6-diacetylpyridine and benzyl carbazate

The Schiff base ligand, N'-(1-{6-[1-(Benzyloxycarbonyl-hydrazono)-ethyl]-pyridin-2-yl)-ethylidene)-hydrazinecarboxylic acid benzyl ester (bc(2)-dap), was synthesized by the reaction of 2,6-diacetylpyridine (dap) with benzyl carbazate (bc) in methanol. Also first row transition metal complexes of the general formula [M(NCS)(2)(bc(2)-dap)]center dot nH(2)O; M = Mn (1), Fe (2), Co (3), Zn (4) or Co (5); n = 0 (1-4) and n = 1 (5), [Fe(bc(2)-dap)(H2O)(2)]center dot 2Cl center dot 4H(2)O (6), [Ni(NCS)(2)(bc(2)-dap)]center dot CH3OH (7) and [Co(NCS)(2)(bc-dap)] (8) have been synthesized using a template method and characterized by spectroscopic techniques and single crystal X-ray diffraction. Complexes 1-4 are isotypic, while compounds 1-6 comprises of discrete mononuclear units with pentagonal bipyramidal geometry. In contrast compounds 7 and 8 adopt octahedral and tetrahedral geometries, respectively. In all of the complexes 1-6, the Schiff base acts as a pentadentate ligand that binds via the pyridine nitrogen, azomethine nitrogen and carbonyl oxygen atoms. The Schiff base ligand occupies the equatorial plane and isothiocyanate anions for 1-5 and water molecules for 6 occupy the axial positions. Compound 7 has octahedral geometry in which the Schiff base ligand acts as a tetradentate ligand and in this case one of the carbonyl oxygen atoms is not involved in coordination. Furthermore, the N-bound isothiocyanate anions are coordinated as terminal ligands. In compound 8, the Schiff base behaves as a bidentate ligand through the azomethine nitrogen and pyridine nitrogen atoms leading to a tetrahedral geometry with the remaining two sites are occupied by isothiocyanate ions. Thermal reactivity of the ligand and complexes (1-8) was studied by TG-DTA and the complexes all undergo endo-followed by exothermic decomposition to give metal oxides, whereas the ligand decomposes completely to give gaseous products. (C) 2017 Elsevier Ltd. All rights reserved.