Electronic insights into aminoquinoline-based PN^HN ligands: protonation state dictates geometry while coordination environment dictates N–H acidity and bond strength

The acidity and bond dissociation free energy of the secondary amine of a P–NH–N tridentate ligand on rhodium(i) and iron(ii) is measured. The amide ligand is planar on rhodium(i) and on cobalt(ii) and in the iron complex with a mer configuration.