Abstract
The present work investigates the complexation behavior of gallium(III) and indium(III) with salts of 6,7-dihydroxy-2-phenyl-4-methylbenzopyrylium and its halogen derivatives in aqueous media. Using classical spectrophotometric techniques (molar ratios and equilibrium shift methods), it was established that in acidic solutions (pH 1–3) a complex is formed in each system with a stoichiometric ratio M(III):R = 1:3. It was demonstrated that the introduction of halogen substituents into the 6,7-dihydroxy-2-phenyl-4-methylbenzopyrylium reagent molecule shifts the optimal pH of complex formation toward a more acidic region, and the magnitude of this shift increases with the electronegativity of the halogen atom. For the investigated complexes, molar absorptivity coefficients and stability constants were determined, confirming the high analytical sensitivity and suitability of these chromogenic systems for trace analysis.
The most intensely colored complexes were obtained with 6,7-dihydroxy-2-(4′-bromophenyl) 4-methylbenzopyrylium, indicating the beneficial effect of halogen substitution on chromophoric properties and light-absorption efficiency. It was found that color development is completed within 10–15 minutes, while the absorbance of the solutions remains stable for at least two hours, ensuring good reproducibility and operational reliability of measurements. The nature of the counter-anion (chloride, bromide, perchlorate) present in the reagent was shown to have no significant effect on the chemical or analytical characteristics of the complexes.
The obtained analytical forms exhibit high stability, strong optical responses, and reproducible spectroscopic behavior, and therefore can serve as a reliable basis for the development of combined spectroscopic methods for the determination of trace amounts of gallium(III) and indium(III). Overall, the results highlight the promising nature and high potential of the studied benzopyrylium derivatives as efficient chromogenic ligands and broaden their prospective ap plication in analytical chemistry.