Stabilization of High‐Valent Fe IV S 6 ‐Cores by Dithiocarbamate(1−) and 1,2‐Dithiolate(2−) Ligands in Octahedral [Fe IV (Et 2 dtc) 3− n (mnt) n ] ( n −1)− Complexes ( n =0, 1, 2, 3): A Spectroscopic and Density Functional Theory Computational Study

A detailed spectroscopic and quantum chemical analysis is presented to elucidate the electronic structures of the octahedral complexes [Fe(Et 2 dtc) 3− n (mnt) n ] n − ( 1 – 4 , n =3, 2, 1, 0) and their one‐electron oxidized analogues [Fe(Et 2 dtc) 3− n (mnt) n ] ( n −1)− ( 1 ox – 4 ox ); (mnt) 2− represents maleonitriledithiolate(2−) and (Et 2 dtc) 1− is the diethyldithiocarbamato(1−) ligand. By using X‐ray crystallography, Mössbauer spectroscopy, and Fe and S K‐edge X‐ray absorption spectroscopy (XAS) it is convincingly shown that, in contrast to our previous studies on [Fe(cyclam)(mnt)] 1+ (cyclam=1,4,8,11‐tetraazacyclotetradecane), the oxidation of 1 – 4 is metal‐centered yielding the genuine Fe IV complexes 1 ox – 4 ox . For the latter complexes, a spin ground state of S =1 has been established by magnetic susceptibility measurements, which indicates a low‐spin d 4 configuration. DFT calculations at the B3LYP level support this electronic structure and exclude the presence of a ligand π radical coordinated to an intermediate‐spin ferric ion. Mössbauer parameters and XAS spectra have been calculated to calibrate our computational results against the experiment. Finally, a simple ligand‐field approach is presented to correlate the structural features obtained from X‐ray crystallography (100 K) with the spectroscopic data.