A DFT/TDDFT study of the structural and spectroscopic properties of Al(III) complexes with 4-nitrocatechol in acidic aqueous solution

The complexation of 4-nitrocatechol in aqueous solution at pH 5 has been studied by molecular spectroscopy combined with quantum chemical calculations. In these physico-chemical conditions, the formation of the two complexes [4ncatAl(H2O)4]+ and [(4ncat)2Al(H2O)2]− has been highlighted. The electronic absorption spectra of the 1:1 and 1:2 complexes of Al(III) with 4-nitrocatechol have been computed using the time-dependent density functional theory and the polarizable continuum model. It turns out that the 6-311+G(d,p) basis set provides a good agreement between experimental and theoretical absorption spectra. This good agreement has allowed the determination of the preferential conformation of the 1:2 complex in aqueous solution. A complete assignment of the UV-Vis absorption and Raman spectra of the complexes has been proposed.