Influence of Steric and Electronic Properties of the Defect Site, Lanthanide Ionic Radii, and Solution Conditions on the Composition of Lanthanide(III) α₁-P₂W₁₇O₆₁^10- Polyoxometalates

Abstract

This study identifies the principles that govern the formation and stability of Ln complexes of the (alpha(1)-P(2)W(17)O(61))(10-) isomer. The conditional stability constants for the stepwise formation equilibria, K(1cond) and K(2cond), determined by (31)P NMR spectroscopy, show that the high log K(1cond)/log K(2cond) ratio predicts the stabilization of the 1:1 Ln/ (alpha(1)-P(2)W(17)O(61))(10-) species. The value of log K(1cond) increases as the Ln series is traversed, consistent with the high charge/size requirement of the basic alpha(1) defect site. The conditional stability constants, K(2), are very low and are highly dependent on the countercations in the buffer. The source of the instability is understood from the crystal structures of the early-mid lanthanide analogues, where the close contact of the (alpha(1)-P(2)W(17)O(61))(10-) units result in severe steric encumbrance. The electronic properties of the alpha(1) defect along with the lanthanide ionic radii and countercation composition are important parameters that need to be considered for a rational synthesis of lanthanide polyoxometalates.

Chirality in Polyoxometalate Chemistry

“…Francesconi examined the speciation of lanthanide complexes of [α 1 ‐P 2 W 17 O 61 ] 10– in depth to develop their luminescence properties. [α 1 ‐P 2 W 17 O 61 ] 10– and lanthanide ions Ln 3+ form predominantly 1:1 POM/Ln complexes, in particular, with later, smaller lanthanides 117. This behavior was further confirmed in organic solution during a collaboration of our groups 118.…”

Chemoselective Catalysis with Organosoluble Lewis Acidic Polyoxotungstates

“…We have already shown that no leaching from the POM/Yb complex took place. Previous work indicated that the complexation constants for the Ln complexes of POMs in water are extremely high9c and are presumably higher in less polar organic solvents.…”

Sensing the Chirality of Dawson Lanthanide Polyoxometalates [α1‐LnP2W17O61]7− by Multinuclear NMR Spectroscopy

“…[33] We decided to follow this approach and recorded the spectra of a series of complexes {a 1 The largest chiral differentiation is obtained for {a 1 -Yb}, which may be attributable to larger paramagnetic shift of the complex. [42] Consequently, this complex was chosen for subsequent studies.…”