Spectroscopic, spectrophotometric and potentiometric studies on 3-(naphthylazo)-5-phenylpyrazole dye and its metal chelates.

The electronic absorption spectra of 3-(naphthylazo)-5-phenylpyrazole dye (L) are studied in some organic solvents of different polarities. The spectra comprise three absorption bands, which are assigned to the corresponding electronic transitions. The pKa value of (L) in ethanol-water mixtures have been determined pH-metrically at different temperatures. The thermodynamic parameters delta G zero, delta H zero and delta S zero have also been evaluated. The successive stability constants of some d-transition elements have been determined pH-metrically at 25 degrees C and mu = 0.1 in 60% (v/v) ethanol-water mixture. A 1:1 and 1:2 (M: L) complexes are formed and evidenced by conductometric studies. The solid complexes of Cu(II) have been isolated and characterized on the basis of elemental analysis, TGA and IR data. The complexes formed between (L) and Cu(II) were studied spectrophotometrically in solutions.