Synthesis, structures and characterisations of truly homoleptic acetonitrile Ln³⁺ complexes in solid state and in solution

Total halide abstraction from LnCl₃ by Ag[Al(OC(CF₃)₃)₄]/CH₃CN has been confirmed for a series of lanthanide metal ions by the structural characterization of [Ln(CH₃CN)_n][Al(OC(CF₃)₃)₄]₃ (n = 9, Ln³⁺ = Nd, Eu, Gd, Dy; n = 8, Ln³⁺ = Tm) complexes. Evidence for the very low coordinating ability of the [Al(OC(CF₃)₃)₄]⁻ anion towards Ln³⁺ ions is provided in the solid state (X-ray, IR and Raman spectroscopy) and in anhydrous acetonitrile solution (conductivity, EPR and NMR measurements). In the solid state homoleptic nine-coordinated acetonitrile species are characteristic for lanthanides for the beginning (Nd) and the middle (Eu, Gd, Dy) of the Ln series, with a mono-capped square antiprismatic arrangement of the N donor atoms around the metal centres; while for those from the end of the series (Tm) eight-coordinated species are representative with a square antiprismatic arrangement. In anhydrous acetonitrile solution, conductivity measurements revealed 3:1 electrolyte types for all compounds. EPR and ¹⁹F NMR line broadening measurements attest lanthanide complexes free of any coordinating [Al(OC(CF₃)₃)₄]⁻ anion.