Controlling thermal stability and volatility of organogold(I) compounds for vapour deposition with complementary ligand design
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Atomic layer deposition (ALD) of gold is being studied by multiple research groups, but to date no process using non-energetic oxidizing co-reactants has been demonstrated. In order to access milder co-reactants, precursors with higher thermal stability are required. We set out to uncover how structure and bonding affect the stability and volatility of a family of twelve organogold(I) complexes with a combined X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and density functional theory (DFT) calculations. Small, unsubstituted phosphonium ylide ligands bind more strongly to Au(I) than their silyl-substituted analogues, but their utility suffers due to their high thermal reactivity. Pentafluorophenyl (PFP–) is introduced as a new, very electronegative ligand for gold vapour deposition precursors, and it was found that the penalty to volatility due to pi-stacking and other intermolecular interactions in the solid state is overshadowed by dramatic improvements to the kinetic and thermodynamic stability of complexes of this ligand. Aurophilic interactions are observed for only one compound in this group. We introduce a new figure of merit to compare and rank the suitability of these complexes as precursors for vapour deposition. Finally, DFT calculations on four compounds that have high figures of merit show a linear correlation between the gold-coordinative ligand bond dissociation energies and the observed decomposition points, substantiating this design strategy.