Novel tripod ligands for prickly self-assembled monolayers

Area of Science:

• Organometallic Chemistry
• Surface Science
• Materials Chemistry

Background:

• Tridentate thioether ligands offer unique coordination properties.
• Self-assembled monolayers (SAMs) are crucial for surface functionalization.
• Tungsten carbonyl complexes provide a stable scaffold for ligand studies.

Purpose of the Study:

• Synthesize novel tripodal thioether ligands: PhSi(CH2SMe)3 (1) and Ph-p-C6H4Si(CH2SMe)3 (2).
• Prepare and characterize tungsten carbonyl chelates using these ligands.
• Investigate the formation and properties of self-assembled monolayers (SAMs) on gold surfaces.

Main Methods:

• Synthesis of ligands 1 and 2.
• Preparation of tungsten carbonyl complexes fac-[W(kappa3-1)(CO)3] and fac-[W(kappa3-2)(CO)3].
• Characterization using single-crystal X-ray diffraction.
• In situ studies of SAM formation via second harmonic generation (SHG) and ellipsometry.
• Ex situ analysis of SAMs using high-resolution X-ray photoelectron spectroscopy (HRXPS), Fourier transform infrared reflection absorption spectroscopy (FTIRRAS), and scanning tunneling microscopy (STM).

Main Results:

• Successful synthesis and characterization of ligands 1 and 2 and their tungsten complexes.
• Observation of a two-stepped SAM formation process: rapid adsorption followed by slow ordering.
• Evidence of dense packing of tripodal anchors and lower density of biphenyl groups on gold surfaces.
• Identification of three distinct sulfur binding states in HRXPS analysis, including thiolate and coordination types.

Conclusions:

• The synthesized tripodal thioether ligands are effective for fabricating ordered SAMs on gold.
• The film formation on gold is a complex process involving initial adsorption and subsequent molecular ordering.
• Surface analysis techniques confirm dense packing and reveal diverse sulfur bonding interactions at the interface.