Re-examination of the formation of dinitrosyl-iron complexes during reaction of S-nitrosothiols with Fe(II)

The reaction of S-nitrosothiol compounds with ferrous ions in solution has been investigated and the generated dinitrosyl-iron complexes have been characterized. During the reaction of S-nitrosocysteamine with Fe(II) in water solution in the presence of a twofold excess (with respect to iron) of cysteamine hydrochloride (CSH), an EPR-silent dinuclear iron complex (complex A of formula [Fe-2(RS)(2)(NO)(4)]) was formed as the major species and was characterized by FAB MS+, UV-Vis, NMR and IR spectroscopies. In the presence of a large excess of CSH (CSH/Fe(II) = 20:1), a green paramagnetic mononuclear complex (complex B of formula [Fe(RS)(2)(NO)(2)](-)) was formed. From EPR and UV-Vis data, and also on the basis of the few crystallographic structures known for similar complexes, complex B is proposed to display a distorted tetrahedral geometry (C-2 nu), approaching a trigonal bipyramid with a missing ligand, with the unpaired electron mainly localized on the d(z2), orbital of the iron characterized by a d(9) electronic configuration. (C) 2001 Elsevier Science B.V. All rights reserved.