Exit transition state of endohedral X@Si20H20 complexes (X=Li+, Na+, K+, Be2+, Mg2+)

The kinetic stability of endohedral X@Si20H20 complexes (X=Li+, Na+, K+, Be2+, Mg2+) has been studied at the B3LYP/6-31G* level of density functional theory (DFT). The transition states (TS) are investigated by the QST3 method of Gaussian 98 package and demonstrated with Intrinsic reaction coordinate (IRC). It is found that K+@Si20H20 cluster has the most stable structure kinetically, that the exit barrier heights (Hexit) for K+ expulsion from or insertion in the cage are 187.38 and 205.58 kcal/mol, respectively. However, the smallest Be2+ dication is not endohedrally encapsulated and the Be2+@Si20H20 cluster is expected to be the least stable structure kinetically. By comparison, other endohedral complexes have a moderate kinetic stability.