Two new silicate structures based on a rhodesite-type heteropolyhedral microporous framework

Two new members of the mero-plesiotype rhodesite series [Sr2Na2(Si8O19)center dot 4H(2)O, abbreviated as TR09; SrNa4-(Si8O19)center dot 4H(2)O, TR10] have been hydrothermally synthesized in Teflon-lined autoclaves at 503 K and structurally characterized using X-ray diffraction single-crystal data. The crystal structures were solved by direct methods and refined to R = 0.021 [TR09; 3317 reflections with I-o > 2 sigma(I-o)] and R = 0.033 [TR10; 5007 reflections with I-o > 2 sigma(I-o)]. Both structures are based on a rhodesite-type microporous heteropolyhedral framework, where two types of channels are within the double silicate layer that alternates with an 'octahedral' O sheet. The large Sr2+ cation constrains to the roughly ellipsoidal shape of the channels. The H2O molecules are located both in the O sheets and in the channels, where they are loosely hydrogen bonded. The crystal-chemical features that allow flexibility to the rhodesite-type microporous heteropolyhedral framework and make it interesting for possible technological applications are discussed.