Performance of exchange–correlation functionals on describing ground state geometries and excitations of Alizarin Red S: Effect of complexation and degree of deprotonation

Ground state optimizations and excited state calculations were performed to analyze the possible anionic forms of Alizarin Red S(ulphonated) and its ML2 type metal complexes formed with palladium(II). Six functionals have been tested (B3LYP, M06-2X, M06, BH&HLYP, PBE0, LC-wPBE, and CAM-B3LYP) with two basis sets (6-311+g(d,p) and TZVP). The relative errors of these functionals in reproducing the experimental UV–Vis absorption wavelengths are reported for the energetically lowest lying isomers. It was found that the degree of deprotonation affects several functionals in a systematic way. M06 and CAM-B3LYP xc-functionals gave the best estimates according to the average relative errors. These two functionals were then used to explore the coordination mode (hydroxy–keto or catechol) of the palladium(II) complexes and the effect of (de)protonation.