STRUCTURAL, SPECTROSCOPIC AND REDOX CHARACTERIZATION OF THE SOLUBLE COMPLEXES [M(SC(6)H(4)NR(2))(4)](2-) AND THE EFFECTS OF N-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-S HYDROGEN-BONDS

The complex [(C2H5)(4)N]Na[Fe(SC6H4NH2-2)(4)] (1) has been synthesized in order to study the influence of ligand hydrogen bonding on the red ox potential of monomeric iron-sulfur complexes. Compound 1 crystalliz es in space group P2(1)/c, with a = 11.747(4), b = 25.058(5), c = 12.3 01(3) Angstrom, beta = 106.22(2)degrees and Z = 4. The related cobalt complex [(C2H5)(4)N](2)[Co(SC6H4NH2-2)(4)] (2) was also synthesized an d found to crystallize in space group Peen with a = 12.544(3), b = 13. 920(3), c = 24.646(15) Angstrom and Z = 4. The average M-S bond length is 2.341(1) Angstrom in 1 and 2.295(2) Angstrom in 2. The electronic absorption spectrum of 2 is consistent with an equilibrium between the respective tetrahedral and pseudo-octahedral complexes [Co(SC6H4NH2-2 )(4)](2-) and [Co(SC6H4NH2-2)(3)](-). The proton NMR spectra of 1 and 2 in saturated CD,CN solutions show unusually broad, isotropically shi fted ligand proton signals, indicative of exchange broadening. This re sult is consistent with the occurrence of [M(SC6H4NH2-2)(4)](2-) compl ex anions in equilibrium with species that could not be identified by H-1 NMR. The cyclic voltammetry data for 1, 12.0 mM in CH3CN, show two irreversible redox waves with E(ox) at -0.50 and -0.25 V, respectivel y, relative to SCE. The peak at -0.50 V is a likely candidate for the redox couple of the complex [Fe(SC6H4NH2-2)(4)](2-). The peak at -0.25 V probably belongs to a pseudo-octahedral iron complex.