Syntheses, characterisation, and computational studies of tungsten hexafluoride adducts with pyridine and its derivatives

A Computational Study on Closed-Shell Molecular Hexafluorides MF6 (M=S, Se, Te, Po, Xe, Rn, Cr, Mo, W, U) - Molecular Structure, Anharmonic Frequency Calculations, and Prediction of the NdF6 Molecule

Quantum chemical methods were used to study the molecular structure and anharmonic IR spectra of the experimentally known closed-shell molecular hexafluorides MF₆ (M=S, Se, Te, Xe, Mo, W, U). First, the molecular structures and harmonic frequencies were investigated using Density Functional Theory (DFT) with all-electron basis sets and explicitly considering the influence of spin-orbit coupling. Second, anharmonic frequencies and IR intensities were calculated with the CCSD(T) coupled cluster method and compared, where available, with IR spectra recorded by us. These comparisons showed satisfactory results. The anharmonic IR spectra provide means for identifying experimentally too little studied or unknown MF₆ molecules with M=Cr, Po, Rn. To the best of our knowledge, we predict the NdF₆ molecule for the first time and show it to be a true local minimum on the potential energy surface. We used intrinsic bond orbital (IBO) analyses to characterize the bonding situation in comparison with the UF₆ molecule.

Stabilisation of [WV F4 ]+ by N- and P-Donor Ligands: Second-Order Jahn-Teller Effects in Octacoordinate d1 Complexes

The first isolated examples of cationic fluoridotungsten(V) complexes are reported as octacoordinate [WF₄ (L)₄ ]⁺ (L=C₅ H₅ N, P(CH₃ )₃ ). The [WF₄ (NC₅ H₅ )₄ ]⁺ cation is synthesised as its [O₃ SCF₃ ]^- salt upon reaction of WF₅ (NC₅ H₅ )₂ with [(CH₃ )₃ Si(NC₅ H₅ )][O₃ SCF₃ ] in excess C₅ H₅ N, whereas [WF₄ {P(CH₃ )₃ }₄ ]⁺ is accessed directly from WF₆ upon reaction with (CH₃ )₃ SiO₃ SCF₃ and excess P(CH₃ )₃ . These salts were characterised by X-ray crystallography and Raman spectroscopy in the solid state. New geometry indices for octacoordinate complexes (τ₈ and τ₈ ') are introduced, allowing for the facile differentiation of trigonal-dodecahedral (TD) and square-antiprismatic (SA) geometries. This has disambiguated the SA geometries of [WF₄ (L)₄ ]⁺ and the geometries of a series of previously reported d⁰ and d¹ MA₄ B₄ complexes. Computational (DFT-B3LYP) studies of [WF₄ (PH₃ )₄ ]^2+/+ and related model systems demonstrate the occurrence of a second-order Jahn-Teller (SOJT) distortion from TD in d⁰ complexes to SA in d¹ complexes, with the degree of SOJT stabilisation being most significant in 5d complexes containing fluorido ligands and monodentate neutral donors.

Stabilisation of [WF5 ]+ and WF5 by Pyridine: Facile Access to [WF5 (NC5 H5 )3 ]+ and WF5 (NC5 H5 )2

The enhanced reactivity of [WF₅ ]⁺ over WF₆ has been exploited to access a neutral derivative of elusive WF₅ . The reaction of WF₆ (NC₅ H₅ )₂ with [(CH₃ )₃ Si(NC₅ H₅ )][O₃ SCF₃ ] in CH₂ Cl₂ results in quantitative formation of trigonal-dodecahedral [WF₅ (NC₅ H₅ )₃ ]⁺ , which has been characterised as its [O₃ SCF₃ ]^- salt by Raman spectroscopy in the solid state and variable-temperature NMR spectroscopy in solution. The salt is susceptible to slow decomposition in solution at ambient temperature via dissociation of a pyridyl ligand, and the resultant [WF₅ (NC₅ H₅ )₂ ]⁺ is reduced to WF₅ (NC₅ H₅ )₂ in the presence of excess C₅ H₅ N, as determined by ¹⁹ F NMR spectroscopy. Pentagonal-bipyramidal WF₅ (NC₅ H₅ )₂ was isolated and characterised by X-ray crystallography and Raman spectroscopy in the solid state, representing the first unambiguously characterised WF₅ adduct, as well as the first heptacoordinate adduct of a transition-metal pentafluoride. DFT-B3LYP methods have been used to investigate the reduction of [WF₅ (NC₅ H₅ )₂ ]⁺ to WF₅ (NC₅ H₅ )₂ , supporting a two-electron reduction of W^VI to W^IV by nucleophilic attack and diprotonation of a pyridyl ligand in the presence of free C₅ H₅ N, followed by comproportionation to W^V .