engleski

Determining structure of copper complexes with nicotinic acid aroylhydrazones using attenuated total reflectance (ATR)

Attenuated total reflectance (ATR) technique was used to study structure of copper complexes with aroylhydrazones derived from nicotinic acid hydrazide and salicylaldehide derivatives having different substituents on the benzene ring. Aroylhydrazones can be involved in keto-enol tautomeric interconversion, when the hydrogen atom in keto form moves from amino to carbonyl group, forming an enol form [1]. In addition, if aldehyde moiety has a hydroxyl group situated in ortho- position with respect to the C=N double bond, the aldehyde part of the molecule can participate in keto-enol equilibrium. Considering different tautomeric forms, aroylhydrazones can act as neutral, monoanionic or dianionic O, N, O tridentate ligands [2]. Different tautomeric forms are characterized by distinctive spectral features and can be distinguished by means of various spectrometric methods, including vibrational spectroscopy. In our previous studies it was found that in solid state and in solvents of different polarities aroylhydrazones appear in keto-amine form, which is generally the most stable one [1, 3]. The ATR spectra of the complexes, formed due to complexation with copper(II) chloride in molar ratios hydrazone/Cu 1/1 and 2/1, pointed that the form of hydrazone was changed depending on substituents on the benzene ring. The spectra of the complexes in 1/1 ratio implied that hydrazones with hydroxyl group on the ortho-position alone or in combination with chloro or methoxy group on the meta-position according to the C=N bond, converted from keto-amine form to enol-imine form. If the two hydroxyl groups were positioned on the ortho- or para-position according to the C=N bond, the ligand retained in keto-amine form. It was also shown that the higher amount of the ligand (2/1 ratio) did not affect complexation, except in case of hydrazone with the methoxy group, for which different spectra were obtained, implying different tautomeric forms in 1/1 and 2/1 complexes.

hydrazones ; metal complexation ; ATR

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