Isostructural bridging diferrous chalcogenide cores [Fe(II)(μ-E)Fe(II)] (E = O, S, Se, Te) with decreasing antiferromagnetic coupling down the chalcogenide series

Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems, but substitution with the heavier chalcogenides selenium and tellurium, however, is much rarer, with only a few examples reported to date. Here we show that treatment of the ferrous starting material [((tBu)pyrpyrr(2))Fe(OEt(2))] (1-OEt(2)) ((tBu)pyrpyrr(2) = 3,5-(t)Bu(2)-bis(pyrrolyl)pyridine) with phosphine chalcogenide reagents E = PR(3) results in the neutral phosphine chalcogenide adduct series [((tBu)pyrpyrr(2))Fe(EPR(3))] (E = O, S, Se; R = Ph; E = Te; R = (t)Bu) (1-E) without any electron transfer, whereas treatment of the anionic starting material [K](2)[((tBu)pyrpyrr(2))Fe(2)(μ-N(2))] (2-N(2)) with the appropriate chalcogenide transfer source yields cleanly the isostructural ferrous bridging mono-chalcogenide ate complexes [K](2)[((tBu)pyrpyrr(2))Fe(2)(μ-E)] (2-E) (E = O, S, Se, and Te) having significant deviation in the Fe–E–Fe bridge from linear in the case of E = O to more acute for the heaviest chalcogenide. All bridging chalcogenide complexes were analyzed using a variety of spectroscopic techniques, including (1)H NMR, UV-Vis electronic absorbtion, and (57)Fe Mössbauer. The spin-state and degree of communication between the two ferrous ions were probed via SQUID magnetometry, where it was found that all iron centers were high-spin (S = 2) Fe(II), with magnetic exchange coupling between the Fe(II) ions. Magnetic studies established that antiferromagnetic coupling between the ferrous ions decreases as the identity of the chalcogen is tuned from O to the heaviest congener Te.