Theoretical investigation of the noble gas molecular anions XAuNgX- and HAuNgX- (X = F, Cl, Br; Ng = Xe, Kr, Ar)

The geometries, atomic charge distributions, vibrational frequencies, and relative energies of the noble gas molecular anions XAuNgX(-) and HAuNgX(-) (X = F, Cl, Br; Ng = Xe, Kr, Ar) were investigated at the MP2 and CCSD(T) levels of theory. The Au-Ng bond length of X(H)AuNgX(-) is mainly dependent on the electronegative fragment bonded to the Au atom rather than on that bonded to the Ng atom. The presence of the right X- anion stabilizes the Au-Ng bond of X(H)AuNg. Based on the interatomic distances and atomic charge distributions, X(H)AuNgX(-) may be better described as X(H)AuNg center dot center dot center dot X- rather than as X(H)(-)center dot center dot center dot AuNgX. The MP2 calculations indicate that, for the Xe, Kr, and Ar molecular anion series, (i) X(H)AuNgX(-) is less stable than the global minimum X(H)AuX- + Ng by ca. 25-35, 33-48, and 37-57 kcal/mol, respectively, (ii) the reaction barriers are ca. 5-14, 3-9, and 2-5 kcal/mol, respectively, when the anion dissociates into X(H)AuX- + Ng through the bending transition state, and (iii) X(H)AuNgX(-) is more stable than the dissociation limit X(H)AuNg + X- by ca. 14-38, 11-30, and 9-25 kcal/mol, respectively.