Ultrafast Water H-Bond Rearrangement in a Metal-Organic Framework Probed by Femtosecond Time-Resolved Infrared Spectroscopy

We investigated thewater H-bond network and its dynamics in Ni2Cl2BTDD, a prototypical MOF for atmospheric waterharvesting, using linear and ultrafast IR spectroscopy. Utilizingisotopic labeling and infrared spectroscopy, we found that water formsan extensive H-bonding network in Ni2Cl2BTDD.Further investigation with ultrafast spectroscopy revealed that watercan reorient in a confined cone up to similar to 50 degrees within 1.3ps. This large angle reorientation indicates H-bond rearrangement,similar to bulk water. Thus, although the water H-bond network isconfined in Ni2Cl2BTDD, different from otherconfined systems, H-bond rearrangement is not hindered. The picosecondH-bond rearrangement in Ni2Cl2BTDD corroboratesits reversibility with minimal hysteresis in water sorption.