Controlling the Thermal Stability and Volatility of Organogold(I) Compounds for Vapor Deposition with Complementary Ligand Design

Abstract

Atomic layer deposition (ALD) of gold is being studied by multiple research groups, but to date no process using non‐energetic 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) compounds using a combination of techniques: X‐ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and density functional theory (DFT). Small, unsubstituted phosphonium ylide ligands bind more strongly to Au(I) than their silyl‐substituted analogues, but the utility of both these ligands suffers due to their poor volatility and substantial thermal decomposition. Pentafluorophenyl (C6F5) is introduced as a new, very electronegative ligand for gold vapor deposition precursors, and it was found that the disadvantage to volatility due to π‐stacking and other intermolecular interactions in the solid state was overshadowed by dramatic improvements to kinetic and thermodynamic stability. We introduce a new figure of merit to compare and rank the suitability of these and other complexes as precursors for vapor 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 temperatures, highlighting and justifying this design strategy.

A Rare Low‐Spin CoIV Bis(β‐silyldiamide) with High Thermal Stability: Steric Enforcement of a Doublet Configuration

“…TGA can also be used to efficiently estimate vapor pressure by employing the Langmuir equation, and the temperature at which 1 displays 1 torr of vapor pressure was estimated with a Clausius-Clapeyron model to be (150.4 AE 0.1) 8C (Figure 6 b). [20] DSC revealed the melting point to be 143 8C and the onset of decomposition (defined as 5 % of the maximum of the first exothermic event) [21] to be 197 8C. The "thermal range" between the 1 torr vapor pressure temperature and the decomposition temperature is often a practical and reliable benchmark of a compounds practicality as an ALD precursor.…”

“…We applied our recently developed "Figure of merit" s that takes key parameters such as thermal range, vapor pressure, and extent of decomposition during TGA into account to quantitatively compare precursors (Table S2). [21,24] A positive (s = À2) where the weak performance of the latter originates from its low volatility. Therefore, 1 was not only competitive with successfully applied Co II precursors but, to the best of our knowledge, represents the only known potential Co IV precursor candidate.…”

“…To contextualize the performance of 1, we subjected two recently reported Co II precursors to thermal analysis: namely CoCl 2 (TMEDA) and Co(DAD) 2 (DAD= tert ‐butyldiazadienyl) (see the Supporting Inforamtion). We applied our recently developed “Figure of merit” σ that takes key parameters such as thermal range, vapor pressure, and extent of decomposition during TGA into account to quantitatively compare precursors (Table S2) . A positive Figure of merit indicates the suitability of a precursor while negative indicates a poor candidate.…”

Ein seltenes Low‐Spin‐CoIV‐Bis(β‐silyldiamid) mit hoher thermischer Stabilität: Sterische Erzwingung einer Dublettkonfiguration

“…Wir nutzten unser kürzlich entwickeltes "Gütemaß" s, das Schlüsselparameter wie den Nutzbereich, den Dampfdruck und das Ausmaß an Zersetzung während einer TGA für einen quantitativen Vergleich berücksichtigt (Tabelle S2). [21,24] Ein positiver Wert impliziert die Eignung einer Vorstufe, ein negativer das Gegenteil. Mit s = 35 ordnet sich 1 zwischen [Co(DAD) 2 ] (s = 64) und [CoCl 2 (TMEDA)] ein (s = À2), wobei das schlechte Resultat des Letztgenannten auf seiner geringen Flüchtigkeit beruht.…”

“…Um die Kennzahlen von 1 in einen geeigneten Kontext zu setzen, unterzogen wir zwei jüngst publizierte Co II ‐Vorstufen derselben Analyse: CoCl 2 (TMEDA) und Co(DAD) 2 (DAD= tert ‐Butyldiazadienyl; siehe Hintergrundinformationen). Wir nutzten unser kürzlich entwickeltes “Gütemaß” σ , das Schlüsselparameter wie den Nutzbereich, den Dampfdruck und das Ausmaß an Zersetzung während einer TGA für einen quantitativen Vergleich berücksichtigt (Tabelle S2) . Ein positiver Wert impliziert die Eignung einer Vorstufe, ein negativer das Gegenteil.…”