A Strategy for the Analysis of Chiral Polyoxotungstates by Multinuclear (31P,183W) NMR Spectroscopy Applied to the Assignment of the183W NMR Spectra of α1-[P2W17O61]10-and α1-[YbP2W17O61]7-

Abstract

This paper describes the complete assignment of the ¹⁸³W NMR spectra of the chiral polyoxometalates α₁-[P₂W₁₇O₆₁]^10- and α₁-[YbP₂W₁₇O₆₁]^7- in aqueous solution. These spectra display each 17 lines of equal intensity with a relatively narrow chemical shift distribution. The identification of signals is based on selective ³¹P−¹⁸³W decoupling and recognition of particular sets of coupling constants for tungsten atoms around the lacunary site. Further assignment is obtained by ¹⁸³W 2D-COSY NMR experiments. We demonstrate herewith a new way for the unambiguous assignment of ¹⁸³W NMR spectra of polyoxotungstates without any symmetry elements or tungsten atoms in special positions. This way relies on the correlation of the magnitude of ²J_W-W coupling constants with the geometry of oxo-bridges in polyoxotungstates. These results open the way to monitor interaction sites of chiral polyoxotungstates with organic ligands.