Two aluminotriphosphates with closely related intersecting tunnel structures involving tetrahedral “AlP” chains and layers: AAl3(P3O10)2, A=Rb, Cs

Two new aluminotriphosphates, RbAl3(P3O10)2 and CsAl3(P3O10)2, were synthesized by solid-state reaction. They crystallize in non-centrosymmetric space groups: C2221 with image, image, image, image for RbAl3(P3O10)2 and C2ce with image, image, image, image for CsAl3(P3O10)2. Their 3D frameworks, built up of corner sharing P3O10 groups, AlO4 tetrahedra and AlO6 octahedra, exhibit several remarkable features. The AlO4 tetrahedra and P3O10 groups are directly associated through the corners, forming helical columns in the Rb-phase and “helicoid” layers in the Cs-phase. The simultaneous presence of AlO4 and AlO6 species, rather rare in phosphates, leads to the formation of closely related [Al3P6O24]∞ layers in both structures, which differ by their stacking mode. The presence of intersecting tunnels running along 〈110〉 and [001] directions, with Rb+ and Cs+ sitting at the intersections, shows the opened character of these two structures.