Density functional theory meta-GGA + U study of water incorporation in the metal-organic framework material Cu-BTC
Eric Cockayne1, Eric B Nelson1
1Materials Measurement Science Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Abstract:
Water absorption in the metal-organic framework (MOF) material Cu-BTC, up to a concentration of 3.5 H2O per Cu ion, is studied via density functional theory at the meta-GGA + U level. The stable arrangements of water molecules show chains of hydrogen-bonded water molecules and a tendency to form closed cages at high concentration. Water clusters are stabilized primarily by a combination of water-water hydrogen bonding and Cu-water oxygen interactions. Stability is further enhanced by van der Waals interactions, electric field enhancement of water-water bonding, and hydrogen bonding of water to framework oxygens. We hypothesize that the tendency to form such stable clusters explains the particularly strong affinity of water to Cu-BTC and related MOFs with exposed metal sites.
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