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Synthesis and characterization of dipicolinic acid hydrazide derivative and Co(III) and Cr(III) complexes

This paper present synthetic procedures to obtain two new mixed ligands coordination compounds with potential pharmacological effects of insulin-mimetic activity. Complex molecules contain biologically important metal ions, Co(III) or Cr(III), multidentate dipicolinic acid hydrazide as primary ligand and diaminohexane as co-ligand. The physico- chemical properties of complex compounds were characterized by IR spectroscopy, thermal analysis (DT-TGA), single crystal X-ray crystallography and cyclic voltammetry. Both complexes crystallize in C 2/c monoclinic space group and have a similar coordination sphere. The metal M(III) ion is coordinated by two tridentate dipicolinate dianions in a distorted [M(N2O)2] octahedral geometry. These mixed ligand chelate complexes are isomorphs and contain metal ion coordinated by two deprotonated hydrazide nitrogen atoms and two oxygen atoms in equatorial plane. The axial coordination sites are occupied by two pyridyl nitrogen atoms. In the crystal structure of both complexes, the molecules are stabilized by intricate pattern of O‒H∙∙∙O, N‒H∙∙∙O and N‒ H∙∙∙Cl hydrogen bond interactions which form an infinite three-dimensional supramolecular network. The hexanediamine cations connect two discrete complex compound molecules via strong N‒H∙∙∙O hydrogen bonds, approximately along -101 crystallographic directions. Thus connected molecules create supramolecular zig- zag motif. The zig-zag structure is additionally stabilized by a series of N‒H∙∙∙Cl interactions that involve chlorine anion, hexanediamine cation and uncoordinated hydrazine nitrogen atom. Interestingly, crystal packing arrangement of CrL is almost identical as in CoL with some minor differences in hydrogen bond geometry. We can conclude based on the X- ray crystallography results that the presence of different metal cation (Cr(III)) in this type of coordination compounds has an almost insignificant impact on crystal structure and molecular stereochemistry. The crystal packing design is driven by the presence of uncoordinated species in the crystal structure, like as, solvent molecules hexanediamine cation, water molecule and chlorine anion, which is well supported by hydrogen bonds pattering. The results of IR spectroscopy, thermal analysis and cyclic voltammetry are in a good agreement with crystal structure determination.

dipicolinic acid hydrazide derivatives, metal complexes, structure characterization

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