[en] The air-free reaction of FeCl2 and H4dobdc (dobdc4- = 2,5-dioxido-1,4- benzenedicarboxylate) in a mixture of DMF and methanol affords Fe2(dobdc), a metal-organic framework isostructural to M2(dobdc) (M = Mg2+, Mn2+, Co2+, Ni2+, Zn2+). The desolvated form of this material has a BET surface area of 1360 m2/g and features 1-D hexagonal pores lined with coordinatively unsaturated Fe2+ cations. O2 adsorption isotherms indicate Fe2(dobdc) irreversibly binds oxygen at 298 K at a capacity over 0.10 mass fraction, corresponding to the adsorption of one O2 molecule per two framework Fe2+ cations. Remarkably, O2 uptake is reversible and the capacity increases two-fold to 0.19 mass fraction at 211 K. Powder neutron diffraction and IR spectroscopy indicate that in both scenarios O2 is coordinated side-on to the iron centers as superoxide at low temperatures and peroxide at room temperature, an observation that is confirmed by Mössbauer spectroscopy. Ideal adsorbed solution theory calculations reveal that Fe2(dobdc) is a promising material for the separation of O2 from air at temperatures well above those currently used in industrial settings.