Synthesis, structure and luminescence property of the three ternary and quaternary europium complexes

Three binuclear europium complexes containing bidentate and tridentate bridging carboxylates with diimines, namely [Eu(m-MOBA)2NO3phen]2, [Eu(2,3-DMOBA)2NO3phen]2 and [Eu(2,3-DMOBA)3bpy]2 (m-MOBA=3-methoxybenzoate, 2,3-DMOBA=2,3-dimethoxy-benzoate, phen=1,10-phenanthroline, bpy=2,2′-bipyridine), have been synthesized and characterized by X-ray diffraction. The two europium(III) ions in each dimer are bridged by the four carboxylato groups in which two of them are the bidentate bridging mode, and the other two the tridentate bridging mode. The crystallographic data and combination bands of infrared spectra of the [Eu(m-MOBA)2NO3phen]2 and the [Eu(2,3-DMOBA)2NO3phen]2 complexes show that the nitrato group is bidentate, and thus each europium(III) ion in the complexes is coordinated with seven oxygen atoms and two nitrogen atoms from phen, leading to a dimeric structure with coordination number 9. Excitation and emission spectra of the europium complexes were observed at 77 K. The 5 D 0 → 7 F J (J=0–4) luminescence spectra show that the europium(III) ion site in the crystals of the three europium complexes has C1 symmetry. The slightly different chemical environments of the europium(III) ions in the [Eu(2,3-DMOBA)3bpy]2 complex is confirmed by its emission spectra.