Abstract The structural and bonding properties of Bi Ac complexes with cyclen-based chelating ligands have been studied using relativistic DFT calculations in conjunction TZ2P all-electron basis sets. Besides the parent cyclen ligand, study has covered its extensions pyridine-type (L py ), carboxylate (DOTA, DOTPA), picolinate (MeDO2PA) phosphonate (DOTMP) pendant arms. effect ring size probed ...