Synthesis, Characterization, and EPR Spectral Studies of the Multi-Metal Species (Fe(MS4)2)3– (M=Mo, W)
G. Delbert Friesen, John W. MacDonald, William E. Newton, William B. Euler, Brian M. Hoffman, Inorganic Chemistry, 1983, 22, 2202 – 2208
Abstract
The complexes [Et4N]3[Fe(MS4)2] (M = Mo, W) have been prepared by reaction of [Et4N]2MS4 with Fe(S2CNC5H5)2 in CH2Cl2 and routinely characterized by infrared and visible spectroscopy. Cyclic voltammetry studies show that, for M = Mo, only the 3–/4– couple is reversible but that, for M = W, 1–/2–, 2–/3–, and 3–/4– couples are observed. The complexes exhibit magnetic moments consistent with the presence of three unpaired electrons, prompting low-temperature electron paramagnetic resonance studies. Signals that are consistent with an S = 3/2 spin state are observed in a variety of solvents for both M = Mo and M = W, and the absence of high-field resonances is indicative of a relatively high value for the zero-field splitting parameter. Values of λ = E/D are estimated for all systems. The potential significance of the similarity of the EPR spectra of these complexes to those of the molybdenum-iron protein of nitrogenase and its cofactor are discussed.