The analysis of the natural bond orbitals (NBO) provides explanations for the distribution of atomic charges (see Table , Supporting Information). The N2 and N5 atoms are important for forming the chelate conformation, while the N3 and occasionally N4 atoms are important for the bridging mode. When the chelating conformation is stable, N2 and N5 atoms possess higher charges in this conformation than in the bridge conformation. When the bridging conformation is stable, the N3 and N4 atoms possess higher charges in the bridge conformation than in the chelate conformation. A higher charge on nitrogen atoms near the metal cation accounts for better charge neutralization in different conformations, building up their stabilities. To inspect -backdonation to the ligand, we compared the frequencies of the normal mode possessing the same symmetry as the LUMO orbital of the ligand 5a (Figure in the Supporting Information) and found that the ligand is not a good -acceptor as opposed to previous studies , which is reflected in a subtle change in the vibration frequency (Table , Supporting Information).