We find complexes for which the protonation energy is negative for both four-and fiveligand complexes, but for the former the structures deviate significantly from the ideal trigonal bipyramidal geometry. Through analysis of three of the 5-ligand complexes we identify a (negative) ligand which makes the single largest contribution, but the analysis is complicated by large non-additive effects. We do show that in addition to the metal ligand interactions, the ligand-ligand interactions also contribute to the low protonation energies by small structural distortions.