Spectroscopic and potenciometric study of aromatic alfa-hidroxyazo compounds and their copper(II) complexes

GABRIELA IBAÑEZ; ALEJANDRO OLIVIERI; GRACIELA ESCANDAR

JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS I

The Royal Society of Chemistry

Lugar: London; Año: 1997 vol. 93 p. 545 - 551

0300-9599

Abstract Three aromatic a‑hydroxy azo dyes, 4‑(2‑hydroxy‑1‑phenylazo) benzenesulfonate (HPBS), 4‑(2‑hiydroxy‑1‑naphthylazo) benzenesulfonate (HNBS) and 4‑(9‑hydroxy‑10‑phenanthrylazo) benzenesulfonate (HPTBS) and their copper(II) complexes have been studied in aqueous solution. The existence of both ground‑ and excited‑state proton transfer leading to equilibria between azo‑enolic and keto‑hydrazonic tautomers in the free ligands has been investigated using 13C NMR, electronic absorption and fluoresence emission spectroscopies, together with semiempirical MO/Cl calculations. The relative stabilities of the tautomers are explained on the basis of the possibility of aromaticity transfer. The formation constants of the CuII complexes have been evaluated using a combination of potentiometric and spectrophotometric titration data. The relative stabilities of the complexes formed with the studied ligands is also discussed.