The question that arises is then: why do amide complexes 9 and 9-crown show evidence for a dz 2 ground state electronic structure while thiolate complexes 8 and 8-crown as well as ammonia complex 10 do not? First, we propose that the π-donating orbitals of the N(TMS)2 ligand in 9 exert a stronger destabilizing influence on the π-symmetry iron dxy and dyz orbitals than the thiolate donor in 8 and certainly more than the ammine donor in 10. Our proposition of a stronger interaction in 9 than 8 is tied to its structure, which shows a short Fe-N bond and a nearly 90° angle between the N(TMS)2 plane and the pincer plane, permitting excellent overlap between dxy and the N px orbital and the dyz and sp 2 -like orbitals aligned roughly along the N-Si bonds. This highly π-donating ligand field closes the energy gap between dz 2 and dxz/dyz in the typical square planar splitting pattern. This explanation alone does not account, however, for the extreme variability in the calculated Mössbauer parameters for 9 depending on whether there is a positive charge near iron. On the basis of our DFT results, we therefore also suggest that the dz 2 orbital can be further stabilized by the presence of a nearby positive charge. Though the complete description of the cation interaction with each of the d orbitals is not elucidated by our work, selective stabilization of the dz 2 orbital may be a result of its shape. A positive charge in the plane of the pincer could interact with the torus-shaped portion of the dz 2 orbital, and one along the z axis can interact with the lobes pointing above and below the pincer plane. The stabilizing interaction of charge with the lobes of dz 2 is illustrated by the comparison between the QRO energies of model A in Figure with optimized 9-crown (Figure ). Model A has positive charge with non-zero projections both onto the z axis and xy-plane while 9-crown has positive charge that is along the z axis. Accordingly, the dz 2 orbital is 0.35 eV lower in energy than the DOMO+1 in 9-crown versus model A.