Synthesis, crystal structure, characterization and biological activity of 2,5-hexanedione bis(isonicotinylhydrazone) and N-(2,5-dimethyl-1H-pyrrol-1-yl)isonicotinamide complexes

• X-ray crystallography of N-(2,5-dimethyl-1H-pyrrol-1-yl)isonicotinamide and its Zn(II) and Hg(II) complexes.
• Metal complexes of 2,5-hexanedione bis(isonicotinylhydrazone) and N-(2,5-dimethyl-1H-pyrrol-1-yl)isonicotinamide [DINH].
• Different stereochemistries for the complexes.
• Antimicrobial activity of the ligand and its complexes.

The reaction between 2,5-hexanedione and isonicotinic acid hydrazide in EtOH gave two products. The ethanol insoluble product was identified as 2,5-hexanedione bis(isonicotinylhydrazone) [HINH] and the soluble ethanol product as N-(2,5-dimethyl-1H-pyrrol-1-yl)isonicotinamide [DINA]. A series of Cr3+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Pd2+ complexes of HINH and Co2+, Cu2+, Zn2+ and Hg2+ complexes of DINA have been synthesized and structurally characterized. Based on the elemental analysis, mass spectra and molar conductance, the complexes have assigned the proposed imperical formulae. The crystal structures of N-(2,5-dimethyl-1H-pyrrol-1-yl)isonicotinamide and its Zn2+ and Hg2+ complexes have been solved by X-ray diffraction having [Zn(DINA)2Cl2] and [Hg(DINA)2Cl2] in a tetrahedral structure. In the DINH complexes, the ligand coordinates as a monodentate through the pyridine nitrogen. On the other hand, HINH behaves as a tetradentate (neutral or binegative) manner with the two metal ions. The magnetic moments and electronic spectra of all complexes provide tetrahedral, square-planar, trigonal biyramid and/or octahedral structure. The thermal decomposition of the complexes revealed the outer and inner solvents as well as the end product. The steady part of [Zn(DINA)2Cl2] and [Hg(DINA)2Cl2] thermograms till 303 and 286 °C indicates the absence of any outside solvents. All compounds have activity against bacteria more than fungi. [Cd4(HINH)Cl8]·3H2O has the highest values.

The reaction between 2,5-hexanedione and isonicotinic acid hydrazide gave two products. One is ethanolic insoluble named as 2,5-hexanedione bis(isonicotinylhydrazone). The soluble one is named as N-(2,5-dimethyl-1H-pyrrol-1-yl)iso-nicotinamide and isolated as crystals and analyzed as shown in the figure. New complexes were synthesized from the two ligands.Figure optionsDownload as PowerPoint slide