Investigation of the Reduced High-Potential Iron-Sulfur Protein from Chromatium vinosum and Relevant Model Compounds: A Unified Picture of the Electronic Structure of [Fe4S4]^2+ Systems through Magnetic and Optical Studies

Magnetization measurements and variable temperature optical spectroscopy have been used to investigate, within the 4-300 K temperature range, the electronic structure of the reduced high-potential iron protein (HiPIP) from Chromatium vinosum and the model compounds (Cat)2[Fe4S4(SR)4], where RS- = 2,4,6-triisopropylphenylthiolate (1), 2,6-diphenylphenylthiolate (2), diphenylmethylthiolate (3), 2,4,6-triisopropylbenzylthiolate (4, 4ʹ), 2,4,6triphenylbenzylthiolate (5, 5ʹ), 2,4,6-tri-tert-butylbenzylthiolate (6), and Cat+ = +NEt4 (1, 2, 3, 4ʹ, 5ʹ, 6), +PPh4 (4, 5).