We report an ab initio molecular dynamics study of the hydration process in a model IRMOF material. At low water content (one molecule per unit cell), water physisorption is observed on the zinc cation but the free⇄bound equilibrium strongly favors the free state. This is consistent with the hydrophobic nature of the host matrix and its type-V isotherm observed in a classical Monte Carlo simulation. At higher loading, a water cluster can be formed at the Zn(4)O site and this is shown to stabilize the water-bound state. This structure rapidly transforms into a linker-displaced state, where water has fully displaced one arm of a linker and which corresponds to the loss of the material's fully ordered structure. Thus an overall hydrophobic MOF material can also become water unstable, a feature that has not been fully understood until now.

We present here a molecular simulation study of the adsorption of CO 2 in a family of IRMOF metalorganic frameworks with varying pore size and chemical nature, as controlled by the linker length and the strength of the MOF-CO 2 interactions. This extension of previous theoretical and experimental characterizations (Walton et al., J. Am. Chem. Soc. 2008, 130, 406-407) provides a coherent explanation and a generic framework to understand the presence or absence of step in the sorption isotherms, in terms of the effect of confinement on the liquid-gas phase diagram of the adsorbate. This branch of the phase diagram is calculated explicitly for CO2 @ IRMOFs, and compared to previous work on families of zeolites and other metal-organic frameworks.