Acta Pharm. 54 (2004) 37-47

Stability of the complexes of some lanthanides with coumarin derivatives. I. Cerium(III)-4-methyl-7-hydroxycoumarin

IRENA P. KOSTOVA,^1*  ILIA I. MANOLOV²  and  MARITZA K. RADULOVA³ 

irenakostova@yahoo.com

¹Department of Chemistry, Faculty of Pharmacy, Medical University, Sofia 1000, Bulgaria
²Department of Industrial Pharmacy, Faculty of Pharmacy, Medical University, Sofia 1000, Bulgaria
³Department of Technology, Faculty of Pharmacy, Medical University, 2 Dunav St., Sofia 1000, Bulgaria

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.

Keywords: Ce(III)-4-methyl-7-hydroxycoumarin, complex stability