Synthesis and characterization of a new thiohydrazone ligand, 3-carboxy-2-hydroxybenzaldehydemorpholine N-thiohydrazone and its metal complexes

Abstract

The reaction of 3-formylsalicylic acid with morpholine N-thiohydrazide in ethanol leading to the formation of a new thiohydrazone, 3-carboxy-2-hydroxybenzaldehydemorpholine N-thiohydrazone (H₂chbmth) is described. This thiohydrazone ligand remained as the thio-keto form in the solid state. However, thioketo- and a small amount of the thiol-tautomeric forms (H₂chbmth and H₃chbmthol, respectively) remain in equilibrium in solution. The reactions of the ligand with different metal salts (in 1 : 1 molar ratio) leading to the synthesis of many new metal complexes have been studied. Depending on pH of the reaction medium and the nature of the metal salt used, the ligand is found to be monobasic tridentate, dibasic tridentate, monobasic bidentate or neutral bidentate giving complexes [Co(H₂chbmth)₂]X₂, [X = NO₃ (11), ½SO₄ (13)]; [Cd(H₂chbmth)(H₂O)₂]SO₄ (21); [M(Hchbmth)X], [M = Cu(II) and X = Cl (1), NO₃ (2), CH₃COO (4); M = Ni(II) and X = Cl (6), NO₃ (7); M = Co(II) and X = NO₃ (12), CH₃COO (14); M = Zn and X = Cl (17), CH₃COO (18); M = Hg(II) and X = Cl (23), CH₃COO (24)]; [Ni(H₂chbmthol)(acac)] (9); [Co(Hchbmth)Cl]·2H₂O (10), [Cu(Hchbmth)H₂O]½SO₄ (3); [Cu(Hchbmthol)]₂ (5); [M(Hchbmthol)X], [M = Ni(II) and X = H₂O (8); M = VO(II) and X = H₂O (15); M = Pd(II) and X = H₂O (16); M = Zn(II) and X = NH₃ (19); M = Cd(II) and X = H₂O (20), NH₃ (22); M = Hg(II) and X = NH₃ (25)]. In situ reactions of metal salts with the ligand components (i.e. 3-formylsalicylic acid and morpholine N-thiohydrazide) in ethanol resulted the same complexes. The complexes are characterized by elemental analyses, magnetic susceptibilities, molar conductances, molecular weights and spectroscopic (IR, ESR, ¹H NMR and UV-visible) data.

Keywords:

• Schiff base
• Thiohydrazone
• Transition metals
• Magnetic susceptibility
• Electronic spectra
• Proton NMR spectra

Acknowledgements

Financial help from the University of Kalyani in the form of Teachers’ Research Grant is gratefully acknowledged. We are thankful to the Regional Sophisticated Instrumentation Centre, Central Drug Research Institute, Lucknow for elemental analyses and some spectroscopic measurements. Facilities provided by the Department of Science and Technology, Govt. of India, New Delhi under Funds for Improvement in Science and Technology are gratefully acknowledged.