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

We report the syntheses and crystal structures of (NH4)(11)[Ln(III)(PMo11O39)(2)]center dot xH(2)O(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 (1) over bar, 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 P-31 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 nu(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 P-31 NMR measurements a direct comparison of Lanthanide Induced (paramagnetic) Shift could be made with the analogous [P(W11O39)(2)](11-) complexes.