Semiconducting Clathrates Meet Gas Hydrates: Xe24[Sn136]

Semiconducting group 14 clathrates are inorganic host-guest materials with a close structural relationship to gas hydrates. Here we utilize this inherent structural relationship to derive a new class of porous semiconductor materials: noble gas filled group 14 clathrates (Ngx[M136], Ng = Ar, Kr, Xe and M = Si, Ge, Sn). We have carried out highlevel quantum chemical studies using periodic Local-MP2 (LMP2) and dispersion-corrected density functional methods (DFT-B3LYP-D) to properly describe the dispersive host-guest interactions. The adsorption of noble gas atoms within clathrate-II framework turned out to be energetically clearly favourable for several host-guest systems. For the energetically most favourable noble gas filled clathrate, Xe24[Sn136], the adsorption energy is –52 kJ/mol/guest at the LMP2/TZVPP level of theory, corresponding to –9.2 kJ/mol/Sn atom. Considering that a hypothetical guestfree Sn clathrate-II host framework is only 2.6 kJ/mol/Sn less stable than diamond-like α-Sn, the stabilization resulting from the noble gas adsorption is very significant.