Isostructural bridging diferrous chalcogenide cores [Fe(μ-E)Fe] (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 [(pyrpyrr)Fe(OEt)] (1-OEt) (pyrpyrr = 3,5-Bu-bis(pyrrolyl)pyridine) with phosphine chalcogenide reagents E = PR results in the neutral phosphine chalcogenide adduct series [(pyrpyrr)Fe(EPR)] (E = O, S, Se; R = Ph; E = Te; R = Bu) (1-E) without any electron transfer, whereas treatment of the anionic starting material [K][(pyrpyrr)Fe(μ-N)] (2-N) with the appropriate chalcogenide transfer source yields cleanly the isostructural ferrous bridging mono-chalcogenide ate complexes [K][(pyrpyrr)Fe(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 H NMR, UV-Vis electronic absorbtion, and Fe Mössbauer. The spin-state and degree of communication between the two ferrous ions were probed SQUID magnetometry, where it was found that all iron centers were high-spin ( = 2) Fe, with magnetic exchange coupling between the Fe 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.