Trivalent lanthanide lacunary phosphomolybdate complexes: a structural and spectroscopic study across the series [Ln(PMo11O39)2]11−

Abstract

We report the syntheses and crystal structures of (NH₄)₁₁[Ln^III(PMo₁₁O₃₉)₂]·xH₂O (where Ln = every trivalent lanthanide cation except promethium) in which two lacunary [PMo₁₁O₃₉]⁷⁻ anions sandwich an 8-coordinate Ln^III cation to yield the complex anion, [Ln^III(PMo₁₁O₃₉)₂]¹¹⁻. The 14 salts crystallise in two different space groups, C2/c or P, but the Ln^III containing anions are isostructural across the whole series, a very rare example of such a complete study. Solid state and solution ³¹P NMR, Raman and IR spectroscopies have been used to prove the stability of [Ln(PMo₁₁O₃₉)₂]¹¹⁻ in aqueous solution. As expected, the Ln^III cation contracts across the series and the Ln–O bond distances decrease uniformly. Interestingly, the splitting in the ν_P–O mode within the [PMo₁₁O₃₉]⁷⁻ unit increases uniformly across the series, which we attribute to the stronger interaction with the smaller, higher charge density Ln^III cation as the series is traversed. For the ³¹P NMR measurements a direct comparison of Lanthanide Induced (paramagnetic) Shift could be made with the analogous [P(W₁₁O₃₉)₂]¹¹⁻ complexes.