Synthesis and characterization of new lanthanide complexes with hexadentate hydrazonic ligands

In this paper, we report the synthesis and the characterization of a novel series of lanthanide (III) complexes with two potentially hexadentate ligands.The ligands contain a rigid phenanthroline moiety and two flexible hydrazonic arms with different donor atom sets (NNN′N′OO and NNN′N′N″N″, respectively for H2L1 (2,9-diformylphenanthroline)bis(benzoyl)hydrazone and H2L2 (2,9-diformylphenanthroline)bis(2-pyridyl)hydrazone).Both nitrate and acetate complexes of H2L1 with La, Eu, Gd, and Tb were prepared and fully characterized, and the X-ray crystal structure of the complex [Eu(HL1)(CH3 COO)2] · 5H2O is presented.The stability constants of the equilibria Ln3+ + H2L1 = [Ln(H2L1)]3+ and Ln3+ + (L1)2− = [Ln(L1)]+ (Ln = La(III), Eu(III), Gd(III), and Tb(III)) are determined by UV spectrophotometric titrations in DMSO at t = 25 °C. The nitrate complexes of H2L2 with La, Eu, Gd and Tb were also synthesized, and the X-ray crystal structures of [La(H2L2)(NO3)2(H2O)](NO3), [Eu(H2L2)(NO3)2](NO3) and [Tb(H2 L2)(NO3)2](NO3) are discussed.