Noble Gas Encapsulated Endohedral Zintl Ions Ng@Pb122- and Ng@Sn122- (Ng = He, Ne, Ar, and Kr): A Theoretical Investigation

The stability of the molecular cage clusters formed by noble gas (Ng) encapsulation in negatively charged Zintl ions like Pb(12)(2-)and Sn(12)(2-)has been investigated through density functional theory and ab initio molecular dynamics simulation studies. The computed structural parameters, energetics, and natural charge values along with the simulation results suggest that they are thermodynamically unstable with respect to dissociation into the respective Ng atom and the parent cage; however, most of these endohedral Zintl clusters are kinetically stable. He@Pb-12(2-), He@Sn-12(2-), Ne@Pb-12(2-), Ne@Sn-12(2-), and H-2 encapsulated Pb(12)(2-)and Sn(12)(2-)clusters preserve their structural integrity throughout the simulation even at 700 K, while Ar@Sn-12(2-), He-2@Pb-12(2-), Ar@Pb-12(2-), and Kr@Pb(12)(2-)are found to retain their structures only at lower temperatures of 150, 500, 500, and 77 K, respectively. Among all of the Ng atom encapsulated clusters, Kr@Sn(12)(2-)is found to be the least stable as the encapsulated Kr atom comes out from the cage, even at 20 K. These results suggest that the stability of these endohedral clusters is truly dependent on the size of the encapsulated atom. Despite high positive electron affinity values of the Ng atoms, the computed NPA results reveal that they gain electrons when encapsulated in an electron -rich cluster. These meager negative charges developed on the Ng atoms indicate a weak van der Waals interaction between the noble gas atoms and the cage atoms, thus making plumbaspherene (Pb-12(2-)) and stannaspherene (Sn-12(2-)) as possible molecular devices to store noble gases. The effect of countercation(s) has been found to be insignificant on the structural parameters and calculated properties of the Ng@Pb(12)(2-)and Ng@Sn-12(2-) Zintl ions. However, it is important to note that unlike the Ng atom encapsulated doubly charged Zintl ions, which are only kinetically stable, the r salt of the Ng atom encapsulated negatively charged Zintl ions is found to be thermodynamically stable. Therefore, our results would incite further studies into the experimental methods through which these molecular carriers for noble gas atoms can be produced.