Cerium(III/IV) and cerium(IV)-titanium(IV) citric complexes prepared in ethylene glycol medium

Cerium(III/IV) and Ce(IV)-Ti(IV) citric complexes were synthesized in ethylene glycol medium under conditions similar to those of the polymerized complex method (PCM). Solution phase H-1, C-13 NMR, solid state C-13 CP MAS NMR and IR spectroscopy, and X-ray powder diffractometry were used to characterize the composition and structure of the synthesized products. Thermal decomposition of the isolated complexes was studied and a scheme of the processes taking place is proposed. Complexes of Ce(III) can be prepared at low temperature (40 degrees C), only. In the presence of Ti(IV) ions, the oxidation takes place even at this temperature. A mixed-metal nature of the Ce(IV)-Ti(IV) complexes is established. The comparison between their composition and the one of analogous lanthanide(III)-Ti(IV) citrates contributes to the elucidation of the complexation process mechanism in the case of the PCM application. The increased charge of the complexation agent in the Ce4+-Ti4+ complex (in comparison with Ln(3+)-Ti4+ citrates) is "compensated'' by the increase of the relative number of the ligands with deprotonated OH group.