Nickel (II) and Copper (II) Complexes Derived from NNOS Donor Unsymmetrical Tetradentate Schiff Base Ligands: Synthesis, Characterization, and Thermodynamic Studies

Abstract

A set of eight unsymmetrical tetradentate Schiff bases (cdPhsalpd = Methyl-2-{[3-(2-hydroxyphenyl)phenylidynenitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; cd3-, 4-, 5-OMesalpd = Methyl-2-{[3-(2-hydroxy 3-, 4-, 5-methoxyphenyl)methylidynenitrilo]propyl} amino-1-cyclopentenedithiocarboxylate; cd5Clsalen = Methyl-2-{[3-(2-hydroxy-5-chloro phenyl)methylidynenitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; cd5Brsalen = Methyl-2-{[3-(2-hydroxy-5-bromophenyl)methylidynenitrilo]propyl}amino- 1-cyclopente- nedithiocarboxylate; cd5NO₂salen = Methyl-2-{[3-(2-hydroxy-5-nitrophenyl)methylidyne- nitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; and cd5SO₃Na = Methyl-2-{[3- (2-hydroxy-5-sodiumsulfitephenyl)methylidynenitrilo]propyl} amino-1-cyclopentenedithi- ocarboxylate, have been obtained by condensation of methyl-2-(3-aminopropylamino) cyclopentenedithiocarboxylate (Hcdpd) with some substituted salicylaldehydes, 2-hydroxy acetophenone, and 2-hydroxy benzophenone, which present a NNOS coordination spheres. Also, the metal complexes (M = Cu, Ni) of these ligands were prepared and characterized by elemental analysis, IR, ¹H NMR, UV-Vis, and mass spectrometry.The formation constants and the thermodynamic free energies were measured using UV-Vis spectrophotometry titration for 1:1 complex formation at constant ionic strength 0.1 M (NaClO₄) at 25°C in DMF. The trend of the complex formation of the nickel and copper complexes is as follows: [M(cdMesalpd)] > [(Mcdsalpd)] > [M(cdPhsalpd)] and [M(cd5OMesalpd)] > [M(cd3OMesalpd)] > [M(cd4OMesalpd)] and [M(cd5OMesalpd)] > [M(cdsalpd)] > [M(cd5Brsalpd)] > [M(cd5Clsalpd)] > [M(cd5SO₃Nasalpd)] > [M(cd5NO₂salpd)]. Our results revealed the thermodynamic formation constant, K _f, and the free energy values for Cu(II) complexes are higher than the Ni(II) complexes.

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Keywords:

• Coordination
• metal complexes
• Schiff base ligand
• thermodynamic
• unsymmetrical

Acknowledgments

We are grateful to Shiraz University Research Council for their financial support.

Notes

^a Solvent is CDCl₃.

^b Solvent is DMSO-d₆.