###### Abstract  
The confined porous environment of metal organic frameworks (MOFs) is an attractive system for studying reaction mechanisms. Compared to flat oxide surfaces, MOFs have the key advantage that they exhibit a well-defined structure and present significantly fewer challenges in experimental characterization. As an example of an important reaction, we study here the dissociation of water--which plays a critical role in biology, chemistry, and materials science--in MOFs and show how the knowledge of the structure in this confined environment allows for an unprecedented level of understanding and control. In particular, combining in-situ infrared spectroscopy and first-principles calculations, we show that the water dissociation reaction can be selectively controlled inside Zn-MOF-74 by alcohol, through both chemical and physical interactions. Methanol is observed to speed up water dissociation by 25% to 100%, depending on the alcohol partial pressure. On the other hand, co-adsorption of isopropanol reduces the speed of the water reaction, due mostly to steric interactions. In addition, we also investigate the stability of the product state after the water dissociation has occurred and find that the presence of additional water significantly stabilizes the dissociated state. Our results show that precise control of reactions within nano-porous materials is possible, opening the way for advances in fields ranging from catalysis to electrochemistry and sensors. metal organic framework; reaction mechanism; confined environment 2018 8 270 2018 270 2018 27  
low external pressures. MOFs are networks of metal ions linked by organic ligands, forming a well-characterized cross-linked structure. Due to their porous nature, gas molecules can penetrate deeply into the MOF network [15] and experience adsorption forces that allow for significantly longer residence times than at surfaces under similar pressures and temperatures, thus fostering an environment much more conducive to trigger, observe, and study desired reactions. MOFs are already well studied for their high surface areas and nano-porous structure as they provide an ideal environment for many applications ranging from gas storage and separation to sensors and catalysis [16; 17; 18; 19; 20]. Amongst the vast amount of existing MOFs, MOF-74 is of great interest since it contains a high density of coordinately unsaturated metal centers (also called open metal sites) in metal-oxide pyramid clusters, which act as active adsorption sites for many small molecules such as H\({}_{2}\), CO, CO\({}_{2}\), NO, CH\({}_{4}\), and H\({}_{2}\)O [21; 22; 23; 24; 25; 26; 27; 28; 29]. In particular, Zn-MOF-74 exhibits a strong affinity to water, making it ideal for examining various water reaction mechanisms [30]. We have already studied the reaction of water molecules alone in Zn-MOF-74 [2; 3; 14; 31], finding direct evidence for water dissociation at only 150 \({}^{\circ}\)C--this was achieved through the use of D\({}_{2}\)O instead of H\({}_{2}\)O, observing a clear fingerprint peak at 970 cm\({}^{-1}\) that corresponds to a O-D bending vibration of OD groups formed upon deuteration of the organic linker [3]. The concerted action between open metal sites and linker phenolate group plays an essential role in breaking up water molecules since water molecule establish strong coordinative bond with metal center via its oxygen and hydrogen bonding interaction with nearby -C-O- moiety from organic linker. With an increase in temperature the water molecule dissociates into D and OD [3]. The OD binds to the open metal sites, while the D atom is transferred to the oxygen of phenolate group. The reaction with water (H\({}_{2}\)O) itself follows of course the same dissociation pathway, but the spectroscopic signature is impossible to detect with H\({}_{2}\)O as hydrogen blue shifts the peak outside the phonon gap of the MOF, where it strongly couples to many other modes.