Structure and Properties of Acidic Protons in Anhydrous Dodecatungstophosphoric Acid, H3PW12O40, As Studied by Solid-State 1H, 2H NMR, and 1H−31P Sedor NMR

Abstract

The binding position and the electronic properties of acidic proton in anhydrous dodecatungstophosphoric acid, H3PW12O40, were studied by means of 1H, 2H NMR, and 1H−31P spin−echo double resonance (SEDOR) NMR techniques. 1H broad line NMR spectrum showed a bell-type resonance line shape with 4.7 kHz line width and MAS NMR spectrum has a single resonance peak, suggesting that the hetero-polyanion PW12O403- provides a single site to the acidic proton. 2H NMR spectrum leads to the quadrupole coupling constant (QCC) of 210 kHz and the asymmetry parameter of the electric-field-gradient tensor (η) of 0.15. The value of QCC suggests that the deuterons are bonded to oxygen atoms in the hetero-polyanion very rigidly, and that any motion of the hetero-polyanion does not take place. A remarkable decay of the 1H−31P SEDOR signal was observed, due to the dipolar interaction between the central 31P and three protons strongly bonded to the hetero-polyanion. The P−H distance was evaluated by simulating the decay behavior...