Axial Perturbation of Intermediate Spin (S=3/2) Iron(III) Complexes with Square Pyramidal N₄X Coordination: Solid State Structures and Electronic Properties

The combination of planar‐directing, strong‐field [N 4 ] ligands with a weak axial field component is known to stabilize five‐coordinate iron(III) complexes in otherwise uncommon spin states. In this work, a series of axially perturbed iron(III) complexes of an [N 4 ] macrocyclic ligand of the Jäger type, [Fe( L )X] (with X: Cl, Br, I, NCS) gave intermediate‐spin ground states with axially steered admixture of the high‐spin state, S =3/2; 5/2. The nature of the electronic ground‐state as deduced from SQUID magnetometry, 57 Fe Mössbauer spectroscopy in the solid, and 1 H NMR and EPR spectroscopies in (frozen) solutions was discussed in the light of the solid‐state structures, which were obtained from single‐crystal X‐ray diffraction. A DFT‐based protocol was established to quantify the axial field effects and, by including relevant [N4] systems, predict the differential equatorial ligand field components.