Tuning Decomposition Temperature: A Structural Study of Ligand Directed Bonding and Fluxionality.

Area of Science:

• Materials Chemistry
• Organometallic Chemistry
• Chemical Synthesis

Background:

• Developing low-temperature decomposing aluminum precursors is crucial for advanced material synthesis.
• Existing precursors often require high temperatures, limiting their application.
• Tailoring ligand structure offers a pathway to control precursor decomposition properties.

Purpose of the Study:

• To design and synthesize novel, easy-to-handle aluminum precursors with decomposition temperatures below 200°C.
• To investigate the relationship between ligand structure, compound fluxionality, and thermal decomposition behavior.
• To assess the viability of these compounds as precursors for material applications.

Main Methods:

• Synthesis of aluminum compounds with systematically varied thiourea ligands.
• Structural characterization using Single Crystal X-ray Diffraction (SCXRD).
• Solution dynamics studied via Nuclear Magnetic Resonance (NMR) spectroscopy (¹H, ¹³C, variable temperature ¹H NMR).
• Mass Spectrometry (MS) and Elemental Analysis (EA) for compound characterization.
• Density Functional Theory (DFT) calculations to elucidate bonding.
• Tandem MS to understand decomposition pathways.

Main Results:

• Eight thiourea ligands with varying steric bulk were synthesized and reacted with aluminum sources.
• Three families of aluminum compounds were formed: Al(Lˣ)₃, MeAl(Lˣ)₂, and EtAl(Lˣ)₂.
• Highly sterically hindered compounds exhibited significant fluxionality and longer Al-N bonds, leading to lower decomposition temperatures (<200°C).
• Solution-state dynamics correlated with solid-state behavior and decomposition profiles.
• DFT calculations provided insights into observed bonding modes.

Conclusions:

• Ligand design and structural control are effective strategies for creating low-temperature aluminum precursors.
• Fluxionality in aluminum compounds directly influences their thermal decomposition onset.
• The synthesized compounds show promise as viable precursors for applications requiring low-temperature processing.