Disorder determined by high-resolution powder diffraction: structure of pentamethylcyclopentadienyllithium

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Crystallography

Background:

• Alkali metal organometallic compounds are crucial in various chemical applications.
• Pentamethylcyclopentadienyl (Cp*) ligands are widely used due to their steric bulk and electronic properties.
• Understanding the solid-state structure of these compounds provides insights into their bonding and reactivity.

Purpose of the Study:

• To determine the crystal structure of pentamethylcyclopentadienyllithium (LiCp*).
• To investigate the structural features, including disorder and chain formation, in LiCp*.
• To characterize the first solid-state structure of a Lewis-base-free alkali metal Cp* compound.

Main Methods:

• High-resolution powder X-ray diffraction data collection.
• Structural modeling using the Rietveld refinement technique.
• Structure determination and disorder analysis via the Maximum Entropy Method (MEM).

Main Results:

• Pentamethylcyclopentadienyllithium (LiCp*) crystallizes in space group R3m.
• The compound forms polymeric 'multidecker' chains along the c-axis.
• Pentamethylcyclopentadienyl anions exhibit coplanarity and threefold rotational disorder, with MEM revealing additional symmetry.

Conclusions:

• The crystal structure of LiCp* has been successfully elucidated.
• The study confirms the polymeric nature and rotational disorder of LiCp* in the solid state.
• This work provides the foundational solid-state structural data for Lewis-base-free alkali metal Cp* complexes.