Theoretical prediction of the host of Helium: (HSiO3/2)n (n = 4, 6, 8) POSS material

Abstract

Polyhedral oligomeric silsesquioxanes (POSS, i.e. (RSiO3/2)n) material is a polyhedral structure with hollow cage shape, which is able to hold other atoms including noble gas atoms. Here, we predict the Hem@(HSiO3/2)n clathrate compounds, (n = 4, 6, 8; the m value can be 1∼6 according to the size of the cage). The (HSiO3/2)6 cage can hold two He atoms at the same time and the He-He bond in He2@(HSiO3/2)6 belongs to partial covalent bond, whose value is 1.348 Å. The desorption energy barriers of the two He atoms in He2@(HSiO3/2)6 escaping from the cage is 56.9 and 21.8 kcal mol−1. Additionally, stacking the (HSiO3/2)6 and (HSiO3/2)8 cages can get Si3(m+1)O3(2m+1)H6 triangular prism cage and Si4(m+1)O4(2m+1)H8 quadrangle prism cage (m = 1∼4), which can also be used as a carrier for storing He atoms. Moreover, Ng@(HSiO3/2)n (Ng = Ne, Ar, Kr, Xe; n = 6, 8) clathrate compounds have also be predicted. Interestingly, the dissociation products of Kr@(HSiO3/2)6 and Xe@(HSiO3/2)6 are not Ng atom escaping from the cage but be a part of the framework of the new cage.