183W INADEQUATE 2D NMR spectroscopy of hetero arsenato-phosphato-tungstate P(V)/As(V) substitution in Dawson-type α-[As(x)P(2-x)W18O62]6- (x = 0-2) and α-[H4As(y)P(1-y)W18O62]7- (y = 0, 1).
The Dawson-type arsenato-phosphato-tungstate α-[AsPW18O62](6-) has been prepared and unambiguously identified for the first time. A comparative study including the four other already known compounds, the symmetric α-[X2W18O62](6-) and unsymmetric α-[H4XW18O62](7-) for X = P(V), As(V), has been performed by spectroscopic (183)W and (31)P NMR. 2-D (183)W INADEQUATE experiments were systematically employed to unequivocally verify structures, assign all resonances, and determine precisely (2)JW-O-W scalar couplings. The effects of P/As substitutions, generating unsymmetric structures, on the NMR observables δW-183, δP-31, (2)JW-O-W, and (2)JW-O-P are discussed in relation to their bond length and bond angle alteration. General trends with respect to NMR parameter variations have been found when filling central cavities with P or As atoms, with less pronounced effects for As than for P. In addition, NMR characterization of three other isomers, i.e., β-[X2W18O62](6-) and γ-[As2W18O62](6-), were also provided for comparison. The present NMR results could serve as representative reference data for understanding the relationship between structure and NMR observables in polyoxotungstates.
Tectospin, Institut Lavoisier de Versailles , 78035 Versailles Cedex, France.
Mohamed
M
Haouas
Israël-Martyr
IM
Mbomekallé
Neus
N
Vila
Pedro
P
de Oliveira
Francis
F
Taulelle