Modeling complexes of H2 molecules in fullerenes

Molecular mechanics calculations indicate that the closure, with the preservation of two H2 guests inside C70 host, of the recently synthesized fullerene complex having the cage with a hole, can prove very difficult. C76 of D2 symmetry seems to be the smallest fullerene for which the endohedral complex with two guest molecules can be obtained while that with three guests must be larger than C80. These results and the analysis of spatial relationships for the recently published semiempirical quantum calculations for 24H2@C60 cast doubts in the reliability of low level quantum calculations for supramolecular systems.