Spectroscopic characterization and the coordination behavior of isonicotinamide with lanthanide ions

The coordination of amide groups to metal ions is important because it may be involved in the interactions between metal ions and proteins. The synthesis and characterization of nine novel lanthanide–isonicotinamide (ina) complexes, including LaCl3, PrCl3, NdCl3, SmCl3, EuCl3, GdCl3, TbCl3, ErCl3 and PrBr3 complexes are reported. The structures of these complexes in the solid state have been characterized by X-ray single crystal diffraction, FTIR, FIR, THz and Luminescence spectroscopy. Isonicotinamide has only one coordination mode in four structures as O-monodentate ligand to coordinate to metal ions, but four kinds of topological structures are observed for lanthanide–isonicotinamide complexes, including LnCl3⋅(C6H6N2O)2⋅4H2O (La, Pr, Nd and Sm), EuCl3⋅(C6H6N2O)2⋅7H2O, LnCl3⋅(C6H6N2O)2⋅6H2O (Gd, Tb and Er) and PrBr3⋅(C6H6N2O)2⋅7H2O. Chloride ions can coordinate to metal ions or hydrogen-bonded. FTIR spectra indicate the formation of four kinds of lanthanide–ina complexes, the extensive hydrogen bond networks after complexation and the coordinations and the changes of the conformation of the ligand. FIR and THz spectra also confirm the formation of lanthanide ion–ina complexes. Luminescence spectra of Eu and Tb-ina complexes have the characteristics of Eu and Tb ions.