The complexation of Al^III, Pb^II, and Cu^II metal ions by esculetin: a spectroscopic and theoretical approach

A. Le Person (1) , A. Moncomble (1) , J.P. Cornard (1)

1 LASIRE - Laboratoire Avancé de Spectroscopie pour les Intéractions la Réactivité et l'Environnement - UMR 8516

UV-visible absorption spectroscopy combined with quantum chemical calculations and, notably, Time-Dependent Density Functional Theory were used to probe the structure of metal complexes with esculetin in dilute aqueous solution, at pH = 5. For the 1:1 complex formation, the studied metal ions can be classified according to their complexing power: aluminum(III) > copper(II) > lead(II). For the three complexes, a chelate is formed with the fully deprotonated catechol moiety and an absorption band is observed at the same wavelength. In all cases, a pronounced ionic character is calculated for metal-ligand bonds. However, the complexes differ in their coordination sphere. Copper and lead are bound to two water molecules leading to a square plane geometry and a hemidirected complex, respectively, whereas aluminum atom has an octahedral environment involving three water molecules and a hydroxide ion. For Al^III only, a 2:1 complex is observed, and the involvement of an aluminum dimer was evidenced.

Domaines: Chimie théorique et/ou physique

A. Le Person, A. Moncomble, J.P. Cornard. The complexation of Al^III, Pb^II, and Cu^II metal ions by esculetin: a spectroscopic and theoretical approach. Journal of Physical Chemistry A, 2014, 118, pp.2646-2655. ⟨10.1021/jp412291z⟩. ⟨hal-00987575⟩