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

MoCl3 (dme) (dme = 1,2-dimethoxyethane) is an important precursor for midvalent molybdenum chemistry, particularly for triply Mo-Mo bonded compounds of the type Mo2X6 (X = bulky anionic ligand). However, its exact structural identity has been obscure for more than 50 years. In search of a convenient, large-scale synthesis, we have found that transMoCl(4)(Et2O)(2) dissolved in dme can be cleanly reduced with dimethylphenylsilane, Me2PhSiH, to provide khaki Mo2Cl6 (dme)(2) in similar to 90% yield. If the reduction is performed on a small scale, single crystals suitable for X-ray crystallography can be obtained. Two different crystal morphologies were identified, each belonging to the P2(1)/n space group, but with slightly different unit cell constants. The refined structure of each form is an edge-shared bioctahedron with overall C-i symmetry and metal-metal separations on the order of 2.8 angstrom. The bulk material is diamagnetic as determined by both the Gouy method and SQUID magnetometry. Density functional theory calculations suggest sigma(6)pi(2)delta*(2) ground state for the dimer with the diamagnetism arising from a singlet diradical broken symmetry electronic configuration. In addition to a definitive structural assignment for MoCl3(dme), this work highlights the utility of organosilanes as easy to handle, alternative reductants for inorganic synthesis.

Automated summary

A convenient large-scale synthesis method for Mo2Cl6(dme)2 has been found, providing single crystals suitable for X-ray crystallography. The refined structures of two crystal morphologies show an edge-shared bioctahedron with C-i symmetry, with metal-metal separations of approximately 2.8 angstrom, exhibiting diamagnetic properties.