The formation of the empty clathrate-hydrate structure is of prime interest in gas hydrate research. This phase can be obtained by pumping out the small guest molecules from the filled clathrate. The most promising starting material is H2-hydrate due to the small size of H2-molecules. The formation route of this phase will be established by in-situ diffraction using the HZB hydrogen pressurising system. This phase should have a negative thermal expansion, which we want to demonstrate experimentally by measuring its temperature-dependent lattice constant.