The Lever redox potential parameterization model is extended to half-sandwich type complexes bearing polydentate boron-based or carbon-based scorpionate-type or pi-aromatic (benzene or p-cymene) ligands, allowing to estimate the electrochemical E-L ligand parameter of a diversity of such polytopal ligands which, thus, are ordered according to their electron-donor character and compared with other ligands. Partial E-L values assigned to each metal ligated arm (2-electron-donor) of the scorpionate ligand (i.e., pyrazolyl, indazolyl or carboxylate groups) and to each unsaturated C=C moiety of pi-benzene (or pi-p-cymene) are also proposed. The studied scorpionate ligands comprise the following basic ones and derivatives: tris(pyrazol-1-yl or indazol-1-yl)borate, tris(pyrazol-1-yl)methane and bis(pyrazol-1-yl)acetic acid. (C) 2012 Elsevier Ltd. All rights reserved.