Synthesis, Structure And Luminescence Properties Of Bipyridine Tetrazolium Tridentate Chelating Ligand Rare Earth Complexes

The research of lanthanide complexes,especially Eu,Tb species,has aroused increasingly attention.this paper,we have designed and synthesized 10 monoclear Eu（Ⅲ）,Tb（Ⅲ）,Gd（Ⅲ）complexes based 6-（¹H-tetrazole-5-yl）-2,2’-bipyridine,6-（¹H-tetrazole-5-yl）-4,4’-dimethyl-2,2’-bipyridine,6-（5-trifluoromethyl-1,2,4-triazol-3-yl）-2,2’-bipyridine and 6-（5-trifluoromethyl-1,2,4-triazol-3-yl）-4,4’-dimethyl-2,2’-bipyridine.The structural and photophysical properties of these lanthanide complexes have been characterized by single-crystal X-ray diffraction,UV-vis absorption spectroscopy,IR spectroscopy,fluorescence spectroscopy.1.Lanthanide（Ⅲ）complexes [Ln（tbpy）₂（DMF）（H₂O）₂]（NO₃）[Ln = Eu（1）,Tb（3）,Gd（5）];DMF = N,N-dimethylformamide)and [Ln（tmbpy）₂（DMF）（NO₃）] [Ln = Eu（2）,Tb（4）,Gd（6）] have been synthesized using the tbpyH and tmbpyH ligands.Single-crystal X-ray diffraction reveals that these Ln（Ⅲ）complexes can be described as a distorted tricapped trigonal prism.It is shown that four mononuclear Ln（Ⅲ）complexes（1-4）are all emissive in the solid state at ambient temperature,and their emissions are assigned to Eu（Ⅲ）⁵D₀→⁷F_J（J= 0-4）transitions for 1-2 and Tb（Ⅲ）⁵D₄→⁷F_J（J = 6-0）transitions for 3-4.It is also noted that the emission intensities of 2 and 4 are stronger than those of 1 and 3,as a result of two water molecules bound to Ln³⁺ in 1 and 3 replaced by one chelate nitrate group in 2 and 4.The emissions of 5-6 are not been detected.2.Using two terdentate ligands（6-（5-trifluoromethyl-1,2,4-triazol-3-yl）-2,2’-bipyridine and 6-（5-trifluoromethyl-1,2,4-triazol-3-yl）-4,4’-dimethyl-2,2’-bipyridine）and Ln（NO₃）3·6H₂O（Ln = Eu,Tb）,four Ln（Ⅲ）complexes with the metal-ligand ratio being 1:1,[Ln（ftbpy）（DMF）₂（NO₃）₂]（7 and 9）and [Ln（ftmbpy）（DMF）₂（NO₃）₂]（8 and 10）have been synthesized.Single-crystal X-ray diffraction reveals that the ftbpyH and ftmbpyH ligands give a mono-anionic tridentate chelating ligand via the N - H bond cleavage of the1,2,4-triazolyl ring and then coordinate with the Ln（Ⅲ）atom to form a distorted tricapped trigonal prism.The emissions of 7-8 are assigned to Eu（Ⅲ）⁵D₀→⁷F_J（J = 0-4）transitions and the emissions of 9-10 are ascribed to Tb（Ⅲ）⁵D₄→⁷F_J（J = 6-0）transitions.The methylation of the ligands has little effect on the structures and luminescence properties of Ln（Ⅲ）complexes.