In this work, a hard model chemometric method was used to determine the stability constants of copper( II) and mercury(II) complexes with the newly synthesized ligand 5-(2-hydroxybenzylidene)-2-thioxodihydropyrimidine-4,6(1H,5H)-dione in acetonitrile by UV-Vis spectrophotometry. The ligand forms stable complexes with both metal cations. The protonation constants of the ligand were also measured in an ethanol-water (1:1) mixture.