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In the context, some lanthanide (Eu(3+), Tb(3+) and Sm(3+)) complexes with conjugated carboxylic acids (pyridine-carboxylic acids derivatives) have been synthesized and characterized. The low temperature fluorescent spectra for these complexes have been measured at nitrogen atmosphere (77 K), indicating that the central Ln(3+) ions locate in an equivalent coordination environment with low symmetry for most of these lanthanide complexes belonging to dimeric or polymeric structure. Therefore, the electronic dipole transition (supersensitive transition) ((5)D(0) --> (7)F(2) for Eu(3+), (5)D(4) --> (7)F(6) for Tb(3+), (4)G(5/2) --> (6)H(9/2) for Sm(3+)) and magnetic dipole transition ((5)D(0) --> (7)F(1) for Eu(3+), (5)D(4) --> (7)F(5) for Tb(3+), (4)G(5/2) --> (6)H(5/2) for Sm(3+)) show the regular change in the corresponding split number of fluorescent spectra, which can be realized to predict the fine structure of lanthanide complexes.

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1 As an active area of research for decades, lanthanides differ from other fluorogens in optical properties, such as long luminescence lifetimes and narrow emission bands in the visible or near-infrared [1][2][3] region, which are appropriate for applications as fluorescent probes [4,5] in biology and medicine and active centers for luminescent materials. Along with the rising considerable attention in the design and assembly of lanthanide complexes, a lot of multichromophoric ligand systems involved in light absorption to lead to highly luminescent complexes of rare-earth ions have been developed [6][7][8][9][10][11][12]. For instance, in the case of Bipy or Phen (Bipy is 2,2'-bipyridine, Phen is 1,10-phenanthroline) components as assistant ligands, the chromophores (L) are arranged to fulfill the coordination requirements of lanthanide (Ln) cations; thus, an antenna-to-cation sensitization step (i.e., an L-to-Ln energy transfer) occurs between partners in a somehow rigid coordination environment. However, a strong quenching of their luminescence is unavoidable in aqueous environments.Many different types of crystal structure of ternary lanthanide complexes with aromatic acids and nitrogen-containing ligands, which show an intense fluorescent character and whose crystals are stable in air, were obtained. Aromatic carboxylic acids provide chelated carboxylates having the capability of more coordinated oxygen atoms, such that higher coordination numbers can be obtained by decreasing molar ratio of ligands, resulting in the dimer or coordination polymer [13][14][15][16].1 This article was submitted by the authors in English.In addition, we can also achieve a molecular assembly of ternary or quaternary lanthanide complex systems with ligands as molecular fragments [17][18][19][20]. Recently, a hydrothermal method has become a fascinating reaction technology to be used in the synthesis of coordination compounds, which can realize some novel structural lanthanide complexes comparing to the general solution evaporation [21,22].In this paper, we report the hydrothermal synthesis of a novel luminescent quaternary dimeric complex [ Tb ( BAA ) 2 ( Phen )( NO 3 )] 2 ( I ) with the assembly of benzoyl acetic acid (BAA), 1,10-phenanthroline and terbium nitrate. The detailed crystal structure and photophysical properties are presented in detail. EXPERIMENTALAll reagents were of analytical grade and used without further purification, except for stock hydrated terbium nitrates prepared by the reaction of lanthanide oxides Tb 4 O 7 and nitric acid.Compound I was prepared by mixing hydrated terbium nitrates, benzoyl acetic acid, and 1,10-phenanthroline in a molar ratio 2 : 3 : 2 in deionized water, and its pH was controlled in a range of 3-4 with a 0.2 mol/l NaOH solution. Stirring of the mixture for 2 h gave a white precipitate, which in succession was placed in a 25 ml Teflon-lined reactor and heated at 433 K in an oven for 3 days. Yellow columnar crystals that formed were studied by X-ray diffraction analysis at room temperatur...