Study of the Formation of Cu(II) Coordination Compounds with 2-Formylpyridine 4-Phenylthiosemicarbazone in Solutions

The complex formation of Cu(II) with 2-formylpyridine 4-phenylthiosemicarbazone (HL) in solutions containing Cu(NO3)2 or Cu2(edta) has been studied (edta4– = ethylenediaminetetraacetate). The UV-Vis spectra of HL show that, in the pH range 5.29–11.00, the maxima are located at 318 nm, whilst the absorption intensity varies slightly. At pH values of 2.00 and 12.00, a bathochromic shift of the maximum is observed. The spectra of the complexes formed in the Cu(NO3)2/HL and Cu2(edta)/HL systems are visually identical and each displays two maxima at 342 and 393 nm which positions remain unaltered with changes in pH. The absorption intensity of the complexes varies only slightly over a rather wide pH range. It has been established that, within the temperature range 10–80°C, the positions of the maxima remain unchanged for the ligand and the complexes, while the absorption intensity decreases only slightly with increasing temperature. Using continuous variations and molar ratio methods it has been established that the complex formed in the Cu(NO3)2/HL system has a Cu(II)-to-ligand stoichiometric ratio of 1 : 1. The conditional stability constant of the complex for this system was determined using Komar’s method and was found to be β = 1.23 × 105 L mol–1 ( $$\log \beta $$ = 5.09). Application of the continuous variations and molar ratio methods to the Cu2(edta)/HL system does not provide an unambiguous result, while Komar’s method proved to be inapplicable.