Molecular boxes as storage containers forH2

All possible conformations of a ${\mathrm{H}}_2$ molecule inside the cubic water octamer ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8$ have been examined using ab initio molecular theory. Starting structures were based on the 14 geometries of the cubic water octamer. In all, optimizations were performed on 39 different ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8·{\mathrm{H}}_2$ structures in order to determine which conformers could contain ${\mathrm{H}}_2$ and which ones would release it. Of the 39 optimizations performed, nine resulted in structures with the ${\mathrm{H}}_2$ contained within the molecular water box. Vibrational frequency analyses were used to determine that five of these nine were minima of the ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8·{\mathrm{H}}_2$ potential-energy surface. An analysis of these structures from the perspective of relative and order of stability and hydrogen bonding was performed. From this analysis, we find a set of hydrogen-bonding topologies that contribute to stabilizing and destabilizing the ${\left({\mathrm{H}}_2\mathrm{O}\right)}_8·{\mathrm{H}}_2$ cage system.