A Strategy for the Analysis of Chiral Polyoxotungstates by Multinuclear (~(31)P,~(183)W)NMR Spectroscopy Applied to the Assignment of the ~(183)W NMR Spectra of alpha_1-[P_2W_(17)O_(61)]~(10-)and alpha_1-[YbP_2W_(17)O_(61)]~(7-)

摘要

This paper describes the complete assignment of the ~(183)W NMR spectra of the chiral polyoxometalates alpha_1-[P_2W_(17)O_(61)]~(10-)and alpha_1-[YbP_2W_(17)O_(61)]~(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 ~(31)p-~(183)W decoupling and recognition of particular sets of coupling constants for tungsten atoms around the lacunary site.Further assignment is obtained by ~(183)W 2D-COSY NMR experiments.We demonstrate herewith a new way for the unambiguous assignment of ~(183)W 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.