Molecular mechanics calculations indicate that the closure, with the preservation of two H-2 guests inside C-70 host, of the recently synthesized fullerene complex having the cage with a hole, can prove very difficult. C-76 of D-2 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 C-80. These results and the analysis of spatial relationships for the recently published semiempirical quantum calculations for 24H(2)@C-60 cast doubts in the reliability of low level quantum calculations for supramolecular systems. (c) 2005 Elsevier B.V. All rights reserved.