, Volume 52, Issue 8, pp 1702-1708

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

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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 [Fe22-SR)2(NO)4nH2O (η1-S, η1-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 μ-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 (δFe = 0.291(1)—0.304(1) mm s–1 at T = 85 K), which are twice as large as δFe 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 θ ≈ 8 K; the effective magnetic moment per iron atom is 1.85 μB.