| Abstract
| - The N-protonated bismercaptoethanediazacyclooctane serves as a bidentate dithiolate ligandto oxidized Fe(NO)2 of Enemark−Feltam notation, E−F {Fe(NO)2},9 mimicking Cys−X−Cys binding ofFe(NO)2 to proteins or thio-biomolecules. The neutral compound is characterized by the well-known g =2.03 EPR signal which is a hallmark of dinitrosyl iron complexes, DNIC's. The Fe(NO)2 unit can be removedfrom the chelate by excess PhS-, producing (PhS)2Fe(NO)2-. Transfer of NO from Fe(H+bme-daco)(NO)2(ν(NO) = 1740, 1696 cm-1) to FeII of [(bme-daco)Fe]2 yields the five-coordinate, square-pyramidal N2S2Fe(NO) (ν(NO) = 1649 cm-1), where NO is in the apical position. Its isotropic EPR signal at g = 2.05 isconsistent with E−F {Fe(NO)}7 formulation. In excess NO, Roussin's red ester-type molecules are formedas dinuclear or tetranuclear species, {(μ-SRS)[Fe2(NO)4]}n (n =1, 2). These well-characterized moleculesfurnish reference points for positions and patterns in ν(NO) vibrational spectroscopy expected to be usefulfor in vivo studies of NO degradation of iron−sulfur clusters in ferredoxins.
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