The nature of the Au–Rg bond in the [AuRg4]2+ (Rg=Ar, Kr and Xe) molecules

A topological analysis of the electron localisation function of the [AuRg4]2+ (Rg = Ar, Kr and Xe) molecules reveals the `closed-shellʹ nature of the Au–Rg binding, which is dominated by electrostatic interactions. A similar finding is obtained by means of the AIM method where the Laplacian of the electron density computed for the bond critical point of the Au–Rg linkage is positive and decreases from 0.163 [AuAr4]2+ to 0.087 [AuXe4]2+. A charge separation according to the Au+1.30[Ar+0.18]4, Au+1.19[Kr+0.20]4 and Au+0.29[Xe+0.43]4 formulas shows an increase of the positive charge on the rare-gas atom and accordingly decrease on the gold atom. The unpaired electron density is localised mainly on Au and the integrated spin density decreases from 0.28 e for [AuAr4]2+ to 0.16 e for [AuXe4]2+.