Different crystal structure and photophysical properties of lanthanide complexes with 5-bromonicotinic acid

Five novel lanthanide (Eu3+ (1), Tb3+ (2), Sm3+ (3), Dy3+ (4) and Gd3+ (5)) complexes with 5-Bromonicotinic acid (5-Brnic) were synthesized and two of them (Tb3+, Sm3+) were characterized by X-ray diffraction. The results reveal that {[Tb(5-Brnic)3(H2O)3]·H2O}n (2) and [Sm(5-Brnic)3(H2O)2·H2O]2 (3) exhibit different coordination geometries and crystal structures. Complex 2 has a one-dimensional chain-like polymeric structure through the bridged 5-Brnic anions which links up two neighboring terbium ions, while Complex 3 forms a dimeric molecular structure. The lowest triplet state energy of 5-Brnic was determined to be 24 330 cm-1 corresponded to the 0-0 transition in the phosphorescence spectrum of its gadolinium complex at 411 nm. The strong luminescent emission intensities of these complexes indicated that the triplet state energy of 5-Brnic is suitable for the sensitization of luminescence of Eu3+, Tb3+, Sm3+ and Dy3+, especially for that of Tb3+ and Dy3+