To gain insight into the Fe-S bonding in 8-crown, which has iron(III) in the most biomimetic S3C coordination sphere, Fe K-edge X-ray absorption spectra were measured. The spectrum showed two pre-edge features at ca. 7112 and 7114 eV. TD-DFT calculations reproduced the pre-edge features of the experimental spectrum (Figure , bottom). Frontier quasi-restricted orbital (QRO) analysis showed three singly-occupied orbitals of primarily Fe 3d character with < 10% S 3p mixing and a LUMO composed of 39.3% Fe 3d character and 21.3% S 3p character (Figure , top). The greater covalency between the Fe and S ligands in the LUMO is responsible for its increased energy. Based on the QRO analysis, the first pre-edge feature at 7112 eV is assigned to excitations of Fe 1s electrons into the three nearly-degenerate singly-occupied orbitals, while the second feature at 7114 eV is assigned to an Fe 1s to LUMO excitation. As expected for iron in the +3 oxidation state, the large contributions of ligand S orbitals to the frontier QROs indicate a large degree of Fe-S bond covalency. These moments are consistent with a well-isolated S = 3/2 ground state. Note that in THF solution, thiolate complex 8 is in equilibrium with its THF adduct 7. At 298 K, the solid-state magnetic susceptibilities of 8, 9, and 10 show cMT of 1.4, 2.3, and 1.9 cm 3 K mol -1 , respectively, under a 5000 Oe applied field. These values are also consistent with an S = 3/2 ground state and little mixing of excited states (Figures ). To further evaluate the zero-field splitting (ZFS) parameters, we measured the low-temperature solution X-band EPR spectra in MeTHF and magnetization curves at ≤ 10 K under field strengths of 1 T to 7 T. The data were fit within the constraints of the usual spin Hamiltonian for an S = 3/2 spin system.