Cu(1+) in HKUST-1: selective gas adsorption in the presence of water.

Spectroscopic evidence for an enhanced binding of Nitric Oxide (NO) to metal centers with lower oxidation states (open Cu(1+) sites) in Cu3(btc)2 (HKUST-1) is presented. The Cu(1+) sites created by thermal treatment or X-ray exposure exhibit a preferential adsorption of NO compared to H2O. This phenomenon demonstrates the potential use of MOFs with lower oxidation state metal centers for selective gas separation.