We investigated the
water H-bond network and its dynamics in Ni2Cl2BTDD, a prototypical MOF for atmospheric water
harvesting, using linear and ultrafast IR spectroscopy. Utilizing
isotopic labeling and infrared spectroscopy, we found that water forms
an extensive H-bonding network in Ni2Cl2BTDD.
Further investigation with ultrafast spectroscopy revealed that water
can reorient in a confined cone up to ∼50° within 1.3
ps. This large angle reorientation indicates H-bond rearrangement,
similar to bulk water. Thus, although the water H-bond network is
confined in Ni2Cl2BTDD, different from other
confined systems, H-bond rearrangement is not hindered. The picosecond
H-bond rearrangement in Ni2Cl2BTDD corroborates
its reversibility with minimal hysteresis in water sorption.