Complexation of Np(V) with pyridine monocarboxylates: a spectrophotometric study

The stability constants for the complexes formed by Neptunyl ion with pyridine monocarboxylates namely picolinic, nicotinic and isonicotinic acids were studied by spectrophotometry technique at 298 K in 0.1 M NaClO₄ medium. The log β determined for complexes ML and ML₂ of Neptunyl with picolinic acid were 2.96 ± 0.04 and 5.67 ± 0.08, with nicotinic acid were 1.34 ± 0.09 and 1.65 ± 0.12 and with isonicotinic acid were 1.52 ± 0.04 and 3.29 ± 0.06 respectively. The higher value of log β and red shift observed in the spectra for NpO₂⁺ picolinate complexes indicates the participation of nitrogen atom in the complexation through chelation whereas in the other two ligands binding is through carboxylate group only. (author)