A series of (thiophenolato)iron(II) complexes, [Fe(TPA)(SAr)](+) (1, Ar = C6H2-2,4,6-Me(3); 2, Ar = C6H4-4-Me; 3, Ar = C6H5; 4, Ar = C6H4-4-Cl), where TPA is tris(2-pyridylmethyl)amine, have been synthesized as models for the isopenicillin N synthase-substrate complex, and [Fe(TPA)(SC6H2-2,4,6-Me(3))](+) (1) has been crystallographically characterized. Complex 1 crystallizes in the monoclinic system, space group P2(1)/a, with cell dimensions a = 14.454(6) Angstrom, b = 9.403(6) Angstrom, c = 21.046(3) Angstrom, beta = 105.43(2)degrees, and Z = 4. The iron(II) center is in a trigonal bipyramidal coordination environment with three pyridine nitrogens forming the equatorial plane and the amine nitrogen and S from the thiophenol occupying the apical positions. The average Fe-N-py distance is 2.126 Angstrom, Fe-N-amine is 2.250(3) Angstrom, and Fe-S is 2.345(1) Angstrom. Complexes 1-4 react with NO at low temperature to form NO adducts. These NO complexes exhibit S-to-Fe charge transfer bands in the visible spectra which are not present in the visible spectrum of [Fe(TPA)(O2CCH3)(NO)](+). They also exhibit S = 3/2 EPR spectra that have higher rhombicity (E/D = 0.041) than that of the acetate analogue (E/D = 0). These effects are attributed to the presence of the thiolate ligand and are analogous to those observed for the enzyme system. Exposure of 1-4 to air at low temperature generates metastable green species corresponding to the one-electron-oxidized iron(III) derivatives. The iron(III) complexes decompose to (mu-oxo)diiron(III) complexes and disulfides under air upon warming to room temperature.