A complex of cerium(III) with 4-methyl-7-hydroxycoumarin was synthesized by mixing water solutions of cerium(III) nitrate and 4-methyl-7-hydroxycoumarin sodium salt in a metal-to-ligand molar ratio of 1:2. The complex was characterized and identified by elemental analysis, conductometry, IR, 1H and 13C NMR-spectroscopy, mass spectral data, DTA and TGA. Thermal analysis of the complex indicated the formation of a compound of the composition Ce(R)2.(OH).5H2O, R standing for the ligand. The reaction of cerium(III) with 4-methyl-7-hydroxycoumarin was studied in detail by spectrophotometric method. The stepwise formation of two complexes, vis., CeR2+ and CeR2+, was established in the pH region studied. The equilibrium constants for 1:1 and 1:2 complexes were determined to be 10.72 and 9.22, respectively.Kompleks cerijevog(III) iona s 4-metil-7-hidroksikumarinom priređen je mješanjem vodene otopine cerijevog(III) nitrata i 4-metil-7-hidroksikumarin natrija u moalrnom omjeru 1:2. Kompleks je karakteriziran i identificiran elementarnom analizom, konduktometrijski, IR, 1H i 13C NMR-spektroskopijom, DTA, TGA i spektrometrijom masa. Termičkom analizom utvrđen je sastav kompleksa kao Ce(R)2.(OH).5H2O. Reakcija cerijevog(III) iona s 4-metil-7-hidroksikumarinom praćena je spektrofotometrijski. U proučavanom pH području utvrđeno je stupnjevito nastajanje dva kompleksa, CeR2+ i CeR2+. Konstante ravnoteže za 1:1 i 1:2 komplekse bile su 10,72, odnosno 9,22
