A conformational polymorph of Ph3PAu[SC(OEt)=NPh] featuring an intramolecular Au•••π interaction

A conformational polymorph, form beta, for Ph3PAu[SC(OEt)=NPh] has been characterised. Like the original structure (form alpha), the molecule features a linear P-Au-S geometry. The difference between molecular structures rests with the relative disposition of the thiolate ligand which places the N-bound aryl ring in close proximity to the gold centre (form beta) rather than the oxygen atom (form alpha). Density functional theory calculations show the molecule with the Au center dot center dot center dot pi interaction is more stable by 5.2 kcal/mol than the one with the Au center dot center dot center dot O contact. The molecular packing of both forms are stabilised by C-H center dot center dot center dot O and C-H center dot center dot center dot pi interactions which make approximately the same contribution to the overall Hirshfeld surfaces. However, key indicators, e.g. crystal packing efficiency and density, and the computational results suggest form beta is the thermodynamically favoured form.