Gradual Release of Strongly Bound Nitric Oxide from Fe2(NO)2(dobdc)

An iron(II)-based metal-organic framework featuring coordinatively-unsaturated redox-active metal cation sites, Fe2(dobdc) (dobdc4– = 1,4-dioxido-2,5-benzenedicarboxylate), is shown to strongly bind ni-tric oxide at 298 K. Adsorption isotherms indicate an adsorption capacity greater than 16 wt %, corre-sponding to the adsorption of one NO molecule per iron center. Infrared, UV-vis, and Mössbauer spec-troscopies, together with magnetic susceptibility da-ta, confirm the strong binding is a result of electron transfer from the FeII sites to form FeIII-NO– adducts. Consistent with these results, powder neutron dif-fraction experiments indicate that NO is bound to the iron centers of the framework with an Fe–NO separation of 1.77(1) Å and an Fe–N–O angle of 150.9(5)°. The nitric oxide-containing material, Fe2(NO)2(dobdc), steadily releases bound NO under humid conditions over the course of more than 10 days, suggesting it, and potential future iron(II) based metal-organic frameworks, are good candidates for certain biomedical applications.