Two tripodal ligands, bis(2-benzimidazolylmethyl)(2-pyridylmethyl)amine (L1) and bis(2-pyridylmethyl)(2-benzimidazolylmethyl)amine (L2), were synthesized. With the third chromophoric ligand antipyrine (Antipy), three series of lanthanide(III) complexes were prepared: [LnL1(Antipy)3](ClO4)3 (series A), [LnL1(Antipy)Cl(H2O)2] Cl2(H2O)2 (series B), and [LnL2(NO3)3] (series C). The nitrate salt of the free ligand H2L1·(NO3)2 and six complexes were structurally characterized: Pr3+A, Y3+A, Eu3+B, Eu3+C, Gd3+C and Tb3+C, in which the two A and three C complexes are isomorphous. Crystallographic studies showed that tripodal ligands L1 and L2 exhibited a tripodal coordination mode and formed 1:1 complexes with all lanthanide metal ions. The coordination numbers of the lanthanide metal ions for the A, B, and C complexes were 7, 8, and 10, respectively. Conductivity studies on the B and C complexes in methanol showed that, in the former, the coordinated Cl- dissociated to give 3:1 electrolytes and, in the latter, two coordinated NO3- ions dissociated to give 2:1 electrolytes. Detailed photophysical studies have been performed on the free ligands and their Gd(III), Eu(III), and Tb(III) complexes in several solvents. The results show a wide range in the emission properties of the complexes, which could be rationalized in terms of the coordination situation, the 3LC level of the complexes, and the subtle variations in the steric properties of the ligands. In particular the Eu3+A and Tb3+A complexes, in which the central metal ions were wholly coordinated by chromophoric ligands of one L1 and three antipyrine molecules, had relatively higher emission quantum yields than their corresponding B and C complexes.
Scopus Subject Areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry