New class of neutral paramagnetic binuclear sulfur-containing iron nitrosyl complexes

Neutral paramagnetic binuclear iron nitrosyl complexes, whose structures and properties differ from those of the known Roussin"s red salt esters, were synthesized for the first time. The iron nitrosyl complexes Fe₂(₂-SR)₂(NO)₄]·nH₂O (¹-S, ¹-N; n = 1 or 2; R is 5-amino-1,2,4-triazol-3-yl (1), 1,2,4-triazol-3-yl (2), 1-methyltetrazol-5-yl (3), or benzothiazol-2-yl (4)) were prepared by the exchange reactions of Na₂Fe₂(S₂O₃)₂(NO)₄ with heterocyclic thiols. According to the results of X-ray diffraction analysis, complex 1 has a centrosymmetrical dimeric structure in which the iron atoms are linked through the -N—C—S structural fragment. Each Fe atom is bound to the N atom of one ligand and the S atom of another ligand. The isomer shifts of complexes 1—4 have virtually equal values (_Fe = 0.291(1)—0.304(1) mm s^–1 at T = 85 K), which are twice as large as _Fe for Roussin"s red salt esters. The iron atoms in complexes 1—4 have the low-spin configuration d⁷ (Fe⁺). The ESR spectra of polycrystalline powders of complexes 1—4 consist of a single Lorentzian line with g = 2.032 and a width of 6—10 mT. The temperature dependence of the magnetic susceptibility of complex 1 in the temperature range of 80—300 K is adequately described by the Curie—Weiss law with 8 K; the effective magnetic moment per iron atom is 1.85 B.