The crystal structures of both compounds 1 and 2 are based on the centrosymetric hetero-polyanion [PMo12O40]
3 and consist of a-Keggin structure in which a central tetrahedron of PO4 is surrounded by twelve MoO6 octahedrons, arranged in four groups of three edge-shared octahedral Mo3O13 units. These groups are connected to one another by their vertices.