Metal-polyhydride molecules are compact inside a fullerene cage

Quantum chemical calculations show that metal-hydride molecules are more compact when they are placed inside a fullerene cage than when they are isolated molecules. The metalhydrogen bond distance in ZrH₄ becomes 0.15 Å shorter when it is placed inside a C₆₀ cage. Metal-polyhydride molecules with a large number of H atoms such as ScH ₁₅ and ZrH₁₆, which are not bound as isolated molecules, are predicted to be bound inside a fullerene cage. It is also shown that two TiH₁₆ clusters are bound inside a bicapped (9,0) carbon nanotube. Possible ways to make metal-hydrides inside C₆₀ and nanotubes are suggested.