Nitric Oxide Adsorption in MIL-100(Al) MOF Studied by Solid-State NMR

Adsorption of nitric oxide (NO) in the metal-organic framework (MOF) MIL-100(Al) is studied by solid-state NMR. Owing to a modified synthesis, no extraframework benzenetricarboxylate is present on the cost of a small amount of extraframework Al(OH)(3) as evident from Al-27, H-1, as well as heteronuclear correlation spectra. Five-coordinated aluminum sites represent about 50% of the aluminum in a dehydrated sample, which remain open for adsorption. With increasing NO loading, a decrease of five-coordinated aluminum with a subsequent increase of six-coordinated aluminum site intensity is found. Additionally, H-1 spin-lattice relaxation time T-1 is decreasing with an increasing amount of NO, which also supports the NO interaction with the MOF because of the paramagnetism of NO. Fourier-transform infrared spectroscopy data further hint at Al-NO interactions.