Study on chrysazin–aluminium(III) interaction in solution by spectroscopy and quantum chemical calculations

Abstract

Spectroscopic (UV–Vis and fluorescence) and theoretical studies were used to assess relevant interaction of aluminium(III) and chrysazin (1,8-dihydroxyanthraquinone) in methanol solution. The complexation reaction has been followed by electronic absorption spectroscopy and chemometric methods of the data set have highlighted the formation of two complexes of stoichiometry 1:1 and 2:1 (metal:ligand) with stability constants of logβ1:1=3.51±0.01 and logβ2:1=5.71±0.01, respectively. Chrysazin has a lower complexing power towards Al(III) than its isomer, alizarin, meaning a significantly lower fixation power of the hydroxy-keto function than that of the catechol function. The theoretical spectra obtained from hypothetical structures by TD-DFT calculations were compared to the experimental ones. This allowed demonstrating, for the free ligand and the two complexes, the absence of tautomeric form in solution. The complexes structures have been elucidated and notably the non-symmetric geometry of the 2:1 complex.