Stability and thermodynamics of ligand‐free tin–gold clusters

The gaseous molecules AuSn, AuSn2, Au2Sn, Au2Sn2, and AuSn3 have been indentified in a mass spectrometric study of the Knudsen effusate from the condensed Au–Sn system. Third‐law enthalpies of the various reactions involving these species, and for the smaller clusters also second‐law enthalpies, were determined from the experimental equilibrium measurements and estimated thermodynamic functions. For the polyatomic molecules several different structures were considered. The dissociation energy D○0 of AuSn(g) was obtained as 252.6±7.2 kJ mol−1 and the heat of formation ΔH○f,298 was evaluated as 414.6±7.2 kJ mol−1. The atomization energies ΔH○a,0 and the standard heats of formation ΔH○f,298 for the polyatomic molecules, in kJ mol−1, are: AuSn2, 483.1±11.7 and 489.4±11.7; Au2Sn, 540.5±20.4 and 493.0±20.4; AuSn3, 788±28 and 477±28; Au2Sn2, 726±35 and 610±35.