Abstract: 2-Hydroxy-3-p-bromophenyl-maleimide (HBPMI) has two acidic functional sites including the ring nitrogen atom and the 3-hydroxy group. Thirteen rare earth metal complexes were prepared by the reactions of HBPMIsodium salt with RECl₃ in DMSO under Ar atmosphere. There complexes were studied by means of IR, UV, ¹H NMR, ¹³C NMR and elemental analysis. The results indicate that it is the deprotonated hydroxy group of the HBPMIthat bonds with RE³⁺, but not the nitrogen. Participation of the adjacent carbonyl in coordination was not found. The composition of the complexes is RECl₃. nH₂O(RE=La-Lu, except Pm, Yb; Lis the HBPMI-oxide anion, n=2～4). RE-O bond is considered to be ionic with some degrees of covalent character. The shift rule of the RE-O bond strength does not conform the rule of tetrad effect. It was found that the conjugation between p-bromophenyl and maleimide moiety in the HBPMI-oxide anion of the rare earth complexes is stronger than in the HBPMIitself, and that the charge is transferred from the negative oxygen to the p-bro-mophenyl moiety.

Key words: Rare earth complexes, Syntheses, Characterization