Neutral Adducts of Molybdenum Hexafluoride: Structure and Bonding in MoF₆(NC₅H₅) and MoF₆(NC₅H₅)₂

The first Lewis acid base adducts of MoF₆ and an organic base have been synthesized, i. e., MoF₆(NC₅H₅) and MoF₆(NC₅H₅)₂. These adducts are structurally characterized with X-ray crystallography, showing that both adducts adopt capped trigonal prismatic structures. The MoF₆(NC₅H₅) and MoF₆(NC₅H₅)₂ adducts are fluxional on the NMR time scale at room temperature. Two different fluorine environments could be resolved by ¹⁹F NMR spectroscopy at -80 °C for the 1 : 2 adduct, MoF₆(NC₅H₅)₂, whereas MoF₆(NC₅H₅) remains fluxional at that temperature. Density functional theory (DFT) calculations aide the assignment of the infrared and Raman spectra. Natural Bond Order and Molecular Electrostatic Potential analyses elucidate the structures and properties of the MoF₆ pyridine adducts. Regions of significantly higher molecular electrostatic potential, i. e., σ-holes, in trigonal prismatic compared to octahedral MoF₆ rationalize the capped trigonal prismatic geometry of the adducts. Whereas MoF₆(NC₅H₅) is stable at room temperature under exclusion of moisture, MoF₆(NC₅H₅)₂ decomposes at 60 °C in pyridine solvent, and the solid slowly decomposes at room temperature after 24 h.