Comparative investigation of polyhedral water cages of (H2O)n (n=20, 24, and 28) encaging CH4 and SF6 as guest molecules

Abstract

Endohedral complexes of X@( H2O)n (n = 20, 24, and 28) fused with guest molecules (X = CH4 and SF6) are computationally analyzed with respect to geometric and energetics by use of B3LYP, B3LYP-D, and M062X methods with 6-311++G(d, p) and cc-PVQZ basis sets. The interaction energies (IEs) of the endohedral CH4@(H2O) n and SF6@(H2O) n complexes represent a clear preference for the latter forms, except for X@(H2O)(20); the SF6@(H2O)(20) is less stable than the CH4@(H2O)(20), unlike the larger complexes, X@(H2O)(24) and X@(H2O)(28). Based on the relative stability of the SF6 guest molecule in larger cages which is consistent with experimental Raman findings, possible structures of SF6@(H2O) n are examined. Our study, in which B3LYP-D and M06-2X methods were employed to elucidate the non-bonding characteristics properly, proposes that CH4 and SF6 molecules exist stably in (H2O) n without noticeable destruction of the cages. However, the X@(H2O)(20) complex expands considerably upon the insertion of the guest molecule in the cage. (C) 2014 Elsevier B.V. All rights reserved.