The coordination of lanthanide ions with picolinamide. The influence of different anions

Abstract

Four kinds of coordination structures formed by lanthanide–picolinamide complexes, including [La(C₆H₆N₂O)₂(H₂O)₅]Cl₃ (La–pa, Pr–pa, Nd–pa, Sm–pa and Gd–pa), [Er(C₆H₆N₂O)₂ (H₂O)₄]Cl₃(H₂O) (Er–pa), [Pr(C₆H₆N₂O)₂(H₂O)₅]Br₃ (PrBr–pa) and [Nd(C₆H₆N₂O)₃(NO₃)₂] (C₆H₆N₂O)(NO₃) (NdN–pa) are reported. The crystal structures in the solid state vary with the change of anions and lanthanide ions as revealed by X-ray single crystal diffraction, FTIR, Raman, FIR and THz spectroscopy. In these crystal structures, the pyridyl nitrogen and carbonyl oxygen of picolinamide are coordinated to metal ions to form a five-membered ring structure or are hydrogen-bonded. The results indicate the differences in the coordination of different lanthanide ions (the Er ion is special for its small atomic radius), the changes of hydrogen bonds and the conformation of the ligands induced by complexation, and the influence of different anions. When nitrate ions are involved in the coordination structure, the coordination number of lanthanide ions is higher. Chloride and bromine ions do not coordinate to metal ions, so lanthanide bromine and lanthanide chloride–pa complexes have similar structures. The results provide models for the coordination structures of lanthanide ions with ligands that have amide groups.