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Abstract
SUMMARY AND CONCLUSION
The chemistry of hydrazine and hydrazide derivatives have an increased interest due to their biological activity and industrial application. Many metal complexed derivatives exhibited significant antiviral activity. from the complexing point of view, organic compounds containing nitrogen and sulphur, nitrogen and oxygen or nitrogen and nitrogen donor atoms are good chelating agents. Therefore, deep chemical and physical studies were done to characterize the complexes of hydrazinecarbodithioic acid [S=C(SH)NH NH2], thiocarbonohydrazide [S=C(NHNH2) NHNH2] hydrazinecarbothioamide [S=C(NH2)NHNH2], hydrazinecarboxamide [O=C(NH2)NHNH2], hydrazinecarboximidamide [NH=C(NH2)NH NH2], with Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II). The present study was aimed to investigate the stability constants, thermodynamic, structural, thermal and biological properties of the complexes
The used theoretical concepts and experimental techniques were discussed in details.
The results obtained can be summarized as following:
1- The protonation constants of the free ligands as well as the stability constants of the formed metal complexes have been determined potentiometrically at different temperatures. The Log KH of the studied ligands at 291 K are found to follow the order :
hydrazinecarbodithioic acid > thiocarbonohydrazide > hydrazinecarbo-thioamide > hydrazinecarboxamide > hydrazinecarboximidamide. This sequence was attributed to the increase of basicity of the studied compounds
The order of the overall stability constants are : Mn < Fe < Co < Ni < Cu > Zn > Cd > Hg, which is in a good agreement with the order found by Irving and Williams.
Thermodynamic parameters, the standard free energy change, ΔGo, the standard enthalpy change, ΔHo, and the standard entropy change, ΔSo were determined. The results show that the ΔGo values are negative for all metal complexes indicating that the complex formation reactions are spontaneous with thermodynamic stability. Negative values of ΔHo show that the exothermic nature of the formed complexes and the enthalpy change is the deriving force for the complexation process. On the other hand, the negative ΔSo values illustrate that the entropy change is not the deriving force and it suggests only high order in the complexed molecules.
In order to investigate the nature of metal-ligand bond in the studied complexes, the thermodynamic parameters were separated into two components, electrostatic (ionic) and non- electrostatic (covalent) terms. The results show that the negative value of ΔGonon is greater than that of ΔG oel suggesting the covalent forces are stronger than the ionic forces. Also the values of ΔHonon are more negative than those of ΔHoel revealing that the metal – ligand bond is mainly covalent in nature. The ratio between the non-electrostatic and electrostatic values for all the complexes remains constant proving thereby the complexing process takes place by a similar mechanism
2- Solid complexes have been prepared and characterized by elemental analysis, IR and 1HNMR spectral studies. The obtained spectra show that all the ligands are bounded to the metal ions through the hydrazinic nitrogen atom and oxygen or sulfur atoms.
3- Thermogravimetric analysis (TGA) of the complexes were carried out to identify their thermal stabilities structure. Also the activation energy and the other kinetic parameters were calculated from Coats-Redfern equation. The data obtained show that the enthalpy values ΔHo have the same trend as those of the activation energy E*. The negative values of the activation entropies ΔSo in most steps of decomposition indicate that the activated complex has a more ordered structure than the reactants. Also ΔHo values are nearly the same that obtained early from potentiometric calculation with opposite sign which reveals that the heat of formation of the complexes equal to the heat of decomposition. The positive value of ΔGo indicates that the decom-position process is non spontaneous in nature.
4- Antimicrobial activities of some complexes compounds against some bacterial and fungal SPP were carried out and it was found that :
• The free ligands have no antimicrobial activity against both groups of micro-organisms.
• Hg-thiocarbonohydrazide complex is the most potent complex and the clear inhabitation zones reached maximally against B. subtilus and B. aureus.
• Ni-complex has no effect against the different species either belong to bacteria or fungi.