To better understand the unique Co-PN bonding situation in 2, DFT studies were performed. The calculated energies of the frontier orbitals are shown in Fig 5A . Consistent with the trigonal planar symmetry surrounding the Co center in 2 and the magnetometry data, the orbitals of d parentage split into a 2-2-1 pattern with two sets of doubly degenerate orbitals; the orbital of dz 2 parentage is lowest in energy and doubly occupied. The remaining four singly occupied orbitals each exhibit substantial Co-N π* character (Fig ). This can be understood by considering an idealized D3h arrangement of three terminal PN ligands (Fig ). In addition to the three N-based symmetryadapted linear combinations (SALCs) that provide σbonding interactions with the central Co center, six Nbased SALCs are available for additional π-bonding interactions. The A2′′ and A2′ combinations do not possess the appropriate symmetry to overlap with d orbitals, but the remaining four SALCs can interact with each orbital comprising the two degenerate e sets (i.e. dxz, dyz, dxy and dx 2 - y 2 ). This bonding situation contrasts that found for related multidentate amide-based ligand architectures, such as (TAML) -or (TREN) suggest that the PNs contribute to a larger ligand field than amides, as indicated by the higher energy charge transfer transitions in 2 (Fig S30 and); a more detailed discussion can be found in the supporting information.