Stabilization of High-Valent FeIVS6-Cores by Dithiocarbamate(1-) and 1,2-Dithiolate(2-) Ligands in Octahedral [FeIV(Et2dtc)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, Mossbauer 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-tetniazacyclotetradecane), 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 incates a low-spin d(4) configuration. DFT calculations at the B3LYP level support this electronic structure and exclude the presence of a ligand pi radical coordinated to an intermediate-spin ferric ion. Mossbauer 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.