Crystal structure and Hirshfeld surface analysis of the elusive trichlorobis(diethyl ether)oxomolybdenum(V)

Synthesis, characterization, X-ray and electronic structures of diethyl ether and 1,2-dimethoxyethane adducts of molybdenum(IV) chloride and tungsten(IV) chloride

The bis(diethyl ether) and 1,2-dimethoxyethane (dme) adducts of molybdenum(IV) chloride and tungsten(IV) chloride are valuable starting materials for a variety of synthetic inorganic and organometallic reactions. Despite the broad utility and extensive use of these 6-coordinate complexes, their syntheses remain unoptimized, and their characterization incomplete after more than three decades. While exploring the ligand exchange behaviour of trans-MoCl₄(OEt₂)₂, we obtained single crystals of this red-orange complex and subsequently compared its structural parameters with those of the recently reported trans-WCl₄(OEt₂)₂. Significantly improved procedures for both MoCl₄(dme) and WCl₄(dme) were developed, and X-ray diffraction data were obtained and analysed. The magnetic properties of the dme adducts were probed, both with Gouy and SQUID magnetometry measurements. The magnetic moment of WCl₄(dme) was smaller than that of MoCl₄(dme), an observation that we attribute to the greater spin-orbit coupling of tungsten. Electronic structure studies were also conducted to probe the preferential trans configuration of the diethyl ether adducts and to assign the UV-Vis spectra of the dme adducts.

"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 trans-MoCl₄(Et₂O)₂ dissolved in dme can be cleanly reduced with dimethylphenylsilane, Me₂PhSiH, to provide khaki Mo₂Cl₆(dme)₂ in ∼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 P2₁/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 Å. The bulk material is diamagnetic as determined by both the Gouy method and SQUID magnetometry. Density functional theory calculations suggest a σ²π²δ*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.