The reactivity of NbX5 (XÂ =Â F, Cl) with lactons, lactams, and the synthesis of the first nucleobase-containing niobium complex

► The family of coordination compounds of NbX5 (X = F, Cl) with oxygen donor ligands has been enlarged. ► The first example of nucleobase-containing niobium complex is presented. ► The ligand-to-reactant molar ratio and the nature of the ligand determine the product of the reaction. ► Dimerization of ε-caprolactam occurs in the reaction between NbCl5 and excess ε-caprolactam.