Na4Ge7O16 center dot 6 H2O and Na2.6Rb0.8H0.6Ge7O16 center dot 6 H2O refined from powder synchrotron X-ray diffraction data

Stirring the microporous germanate Ag4Ge7O16 . 6 H2O in aqueous sodium chlo ride solution leads to a fully-ion-exchanged product Na4Ge7O16 . 6 H2O, spa ce group R3m, Z = 1 with a = 7.759(3) Angstrom, alpha = 89.08(2)degrees, V = 466.9 Angstrom (3). Similar treatment of Rb3HGe7O16 . 3 H2O yields a part ially-ion-exchanged material, Na4-x-yRbxHyGe7O16 . n H2O, (x = 0.80(4), y a pproximate to 0.6, n approximate to 6), with a = 7.759(5) Angstrom, alpha = 89.53(4)degrees, V = 467.0 Angstrom (3). The disordered structures have be en refined using the Rietveld method from powder synchrotron X-ray diffract ion data. The relationship between the structures of the two materials is d iscussed.