The relations between (1)H and (31)P nuclei are investigated by multinuclear and multidimensional nuclear magnetic resonance (NMR) spectroscopy in order to obtain structural information along the transformation of the thorium phosphate hydrogen phosphate hydrate (TPHPH) into the thorium phosphate diphosphate (TPD) when heating. The raw sample obtained at 120 degrees C was heated at 300, 400, 600, 800 or 1100 degrees C and then studied at room temperature. Single acquisition on (1)H and (31)P nuclei, cross-polarization (CP) at the magical angle spinning, Lee-Golburg homonuclear decoupling in two-dimensional experiments, rotational echo double resonance (REDOR and CP-REDOR) and heteronuclear correlation (HETCOR) were performed. These experiments contribute to evidence the differences between the raw sample and that heated. Indeed, above 300 degrees C, hydrogen phosphate groups (HPO(4)) are completely condensed as diphosphate entities (P(2)O(7)). These results confirm that the TPHPH is successively transformed into a low-temperature form of the TPD (called alpha-TPD), then into its well-known beta-form above 950 degrees C.