Formation constants and thermodynamic parameters of α-pyridoin thiosemicarbazones with divalent metal ions

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The proton–ligand stability constants of α-pyridoin thiosemicarbazone, α-pyridoin 2-methylthiosemicarbazone, α-pyridoin 4-methylthiosemicarbazone and α-pyridoin (4-phenylthiosemicarbazone) as well as the formation constants of their chelates with CuII, NiII, CoII, ZnII and MnII have been determined. The Calvin–Bjerrum pH titration techniques, as modified by Irving and Rossotti, were employed in aqueous media at different ionic strengths and temperatures. The stability constants of the complexes follow the order: CuII > NiII > CoII > ZnII >MnII which is in accord with the Irving–Williams series. The chelates derived from α-pyridoin 4-phenylthiosemicarbazone have relatively higher stability constants, which may be attributed to the presence of the benzene ring in the chain.

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