Bonding descriptions were obtained from the DFT-optimized structures. The electronic structures of 1 and 2 are similar, with minor variations due to ligand differences. The highest energy occupied valence MOs consist of Cl 3p, Co 3d and P 3p levels, which are intermixed and spread over a range of occupied MOs (Figure ). Co-based orbitals also weakly overlap with the Cl 3s (and O 2p and O 2s in 2) levels. The unoccupied valence MOs contain two sets of contributions. The first set of vacant MOs consists of Co 3d orbitals with t2 symmetry, which are singly-occupied. Second, the π* MOs on the PNNP ring system overlap with occupied Co 3d levels. This is a back-bonding interaction, which leads to a small percentage of Co 3d character mixed into the PNNP π* system, with an orbital energy higher than the Co 3d t2 vacant orbitals.