In Cat1 the three negative hydrazine ligands ) are all equatorial as shown in Figure , whereas the neutral ligands are 2,4-dihydroimidazoles. The ligand that makes the single largest contribution to the protonation energy is the negative ligand (ligand 4), trans to the equatorial neutral ligand (ligand 6), followed by ligands 6, 7 (the axial ligand), 5, and 3. Changing ligand 4 to an NH - 2 increases the protonation energy from -6.2 to +1.3 kcal/mol. Changing both ligands 4 and 6 increases the protonation energy further to +5.8 kcal/mol, and the protonation energy remains positive for all other substitutions as shown in Figure . While this analysis points towards ligand 4 as the main reason for the exergonic protonation energy, it should be noted that the ligand-effects can be significantly non-additive as shown in Figure .