Synthesis, Crystal Structure And Luminescence Properties Of Europium Aromatic Carboxylic Acid

Eighteen ternary complexes of Eu(III), seven quaternary complexes of Eu(III) mixed NO₃^-, four quaternary complexes of Eu(III) doped with terbium(III), yttrium(III) or lanthanum(III) have been synthesized. In these complexes, eleven aromatic carboxylic acids were used as the first ligand, and 1,10-phenanthroline (2,2'-bipyridine or bathophenanthroline) as the second neutral ligand. The compositions of these complexes were confirmed by elemental analysis (C, H, N) and EDTA titration for rare earth.The complexes were characterized by means of IR, UV, TG-DTG and SEM methods. In these complexes, the Eu(HI) ions were bonded to the oxygen atoms of carboxylate and the nitrogen atoms of neutral ligands. The thermal stability rule for these complexes is: complexes with bath coligand > complexes with phen coligand > complexes with bipy coligand. The thermal stability of those complexes doped with other rare earth ions is lower than that of the corresponding ternary complexes. The structures of three ternary complexes Eu(o-MOBA)₃ phen·H₂O (1), Eu(m-MOBA)3phen·H_O(2) and Eu(NO₃)₃(phen)₂(3) have been determined using X-ray diffraction. Both 1 and 2 exist as binuclear molecules, and crystallize in triclinic, space group P₁. The crystallographic parameters are as follows: 1, α = 11.436(4)A, b = 12.759(4) A, c = 13.139(4) A, a = 66.818(4)°,β = 83.533(4)°, γ = 70.335(3)°;2, α = 10.5253(9) A, b = 11.783(1) A, c = 14.410(1) A, a = 108.915(1)°,β =94.919(1)°, γ = 108.725(1)°. Complex 3 exists as mononuclear molecules, and crystallize in monocline, space group C2/c. The crystallographic parameters are as follows: 3, a = 9.5259(7) A, b = 15.472(1) A, c = 17.196(2) A;a = 90°, β = 93.462(1)°, γ = 90°.The luminescence spectra of the Eu(III) complexes show that the positions of emission peaks remain unchanged. However, the emission intensity of the complexes changes due to the different ligands or different doped metal ions. The major works in this paper are focused on: (i) the best luminescent complex is chosen in each series;(ii) the influence of different substituents on the luminescent intensity;(iii) the influence of different carbon chain connected with carboxyl on the luminescent intensity;(iv) the influence of NO₃^- on the luminescent intensity;( v ) the influence of the doped rare earth ions on the luminescent intensity. These results will provide valuable information for the synthesis of new effective rare earth luminescent materials.