Spectrophotometric determination of the stability constants of the complexes between the Ni2+ ion and some substituted salicylic acids in aqueous solution

Complexation of 5-fluorosalicylic acid with copper(II): A pH-potentiometric, UV–vis spectroscopic, and electron spin resonance study by the two-dimensional simulation of spectra

“…The pK a for the phenolic hydroxy group of 5-halogenosalicylic acids falls between 12 and 13, as a consequence of the strong intramolecular hydrogen bond [29][30][31][32]: it is too high to be precisely determined by pH-potentiometry. The proton loss of this group of the free ligand does not play any role below pH 11, where our measurements were carried out.…”

“…The simple model including the metal complexes Cu 2+ (aqua complex), [CuLH À1 ] and [CuL 2 H À2 ] 2À , generally accepted in earlier papers for salicylic acid derivative ligands [28][29][30][31][32][33], proved to be unsatisfactory for the descrip- Table 1 pH-potentiometric formation constants as log b and absorption spectral data for the metal complexes detected in aqueous solutions in the copper(II)-5- tion of the set of ESR spectra. Good spectral fit could be achieved only if several new major and minor species were taken in consideration.…”

Effect of fluorine position on the coordinating ability of fluorosalicylic acids — An experimental study complemented with computations

“…Similarly to the 5-halogenosalicylic acids, the pK a of the phenolic OH is too high to be precisely determined by pH-potentiometry. It falls between 12 and 13 [51][52][53][54], which can be explained by the strong intramolecular hydrogen bond formed between the carboxylate group and the phenolic OH). The proton loss from this group of the free FSA ligands did not play any role below pH= 11.…”

“…Either the simple model including the metal complexes Cu 2+ (aqua complex), [CuLH −1 ] and [CuL 2 H −2 ] 2− generally accepted in earlier papers for salicylic acid derivative ligands [51][52][53][54]56,57] or the inclusion of the hydroxide-bridged dimeric species [Cu 2 L 2 H −3 ] − shown by the combined pH-potentiometric and UV-Vis spectroscopic measurements (see previous discussion) proved to be unsatisfactory for the rationalization of the ESR spectra sets. Three new major or minor species had to be taken into consideration in order to reach a good agreement between the experimental and the calculated curves.…”

Speciation of 2-Hydroxybenzoic Acid with Calcium(II), Magnesium(II), and Nickel(II) Cations in Self-Medium

“…Moreover, it represents the simplest model for the humic acids present in soil. Thus, the complexation equilibria of H 2 L with several cations has been studied by potentiometric as well as spectrophotometric methods. − However, despite the relevance of the ligand, only few quantitative data regarding equilibria occurring between H 2 L and Ca(II), Mg(II), and Ni(II) ions in aqueous media have been reported, and the results are often contradictory (Table ).…”