"MoCl₃(dme)" Revisited: Improved Synthesis, Characterization, and X-ray and Electronic Structures

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• The precursor "MoCl3(dme)" (dme = 1,2-dimethoxyethane) is crucial for midvalent molybdenum chemistry, especially for Mo-Mo triple bonds.
• The precise structural identity of "MoCl3(dme)" has remained elusive for over fifty years.

Purpose of the Study:

• To establish a convenient, large-scale synthesis for "MoCl3(dme)".
• To definitively determine the structure of the molybdenum precursor.
• To explore the utility of organosilanes as reducing agents in inorganic synthesis.

Main Methods:

• Reduction of trans-MoCl4(Et2O)2 in dme using dimethylphenylsilane (Me2PhSiH).
• Isolation and purification of the product, Mo2Cl6(dme)2.
• X-ray crystallography for structural determination.
• Gouy method and SQUID magnetometry for magnetic property analysis.
• Density functional theory (DFT) calculations for electronic structure analysis.

Main Results:

• A high-yield (∼90%) synthesis of khaki Mo2Cl6(dme)2 was developed using dimethylphenylsilane.
• Two distinct crystal morphologies were identified, both belonging to the P21/n space group, revealing an edge-shared bioctahedral structure with a Mo-Mo bond length of approximately 2.8 Å.
• The bulk material was found to be diamagnetic.
• DFT calculations indicated a σ2π2δ*2 ground state with diamagnetism arising from a singlet diradical electronic configuration.

Conclusions:

• The structure of "MoCl3(dme)" has been definitively assigned.
• Dimethylphenylsilane is presented as an effective and convenient reducing agent for inorganic synthesis.
• The study provides insights into the electronic structure and bonding of midvalent molybdenum dimers.