The co-crystallisation of benzene-1,3,5-tris(methylenephosphonic acid) [C9H15O9P3] 1 with guanidinium chloride [CH6N3]Cl, yields compound 2 that possesses the following composition [CH6N3]3 [C9H13O9P3] [C9H14O9P3]. The crystal structure of this supramolecular material, which possesses six crystallographically inequivalent phosphorus atoms, is reported. The packing of this 3D-supramolecular arrangement reveals the presence of 33 hydrogen bonds engaging the couples phosphonic acid-guanidinium and phosphonic acid-phosphonic acid. Solid-State MAS NMR of the sensitive 31P nucleus in this supramolecular arrangement is used in order to develop alternative analytical method to get information on supra-molecular assemblies. 31P through-space single quantum – double quantum correlation experiments have been performed leading to two possible assignments of the 6 crystallographic P sites to the corresponding resonances in the 1D 31P MAS NMR spectrum.