Résumé
With through space and through bond experiments in two-dimensional NMR we analyze the transformation from the thorium phosphate-hydrogen phosphate hydrate (TPHPH) to the
β form of the thorium phosphate diphosphate (
β-TPD) in relation with the phosphorus networks. These techniques are complementary: the through space coupling gives an insight on the dipolar phosphorus networks while the through bond coupling is particularly efficient in the detection of the P
2O
7 groups. With these experiments we show that in a first step, by heating the precursor TPHPH above 250
°C, it transforms into an
α form of TPD. This transformation is due to the complete condensation of hydrogen phosphate groups HPO
4 into P
2O
7 entities. By heating
α-TPD above 950
°C it transforms into its well-known
β form. The
α form is characterized by a hygroscopic behavior: some water molecules are present near the P
2O
7 groups that makes non-equivalent their phosphorus nuclei. PO
4 dipolar networks are always present in the
α form. The main effect of these PO
4 and P
2O
7 units is to give the system a channel structure and the water enters in them.