Abstract

Two new members of the mero-plesiotype rhodesite series (KCa2Na[Si8O19]·5H2O, abbreviated as TR03; a 6.5850, b 23.776, c 7.0250 Å; Pn21m; and KNa3Sr[Si8O19] ·4.3H2O, TR04; a 6.5699, b 23.7225, c 7.0225 Å, β 91.81°; P21/m) have been hydrothermally synthesized in Teflon-lined autoclaves at 200–230 °C and structurally characterized using X-ray diffraction single-crystal data (Bruker-AXS Smart Apex diffractometer equipped with a CCD area detector, MoKα radiation). The crystal structures were solved by direct methods and refined to R = 0.090 [TR03; 2634 reflections with Io > 2σ(Io); {010} twinning by merohedry] and R = 0.062 [TR04; 4535 reflections with Io > 2s(Io)]. Both structures are based on a rhodesite-type porous heteropolyhedral framework, where two types of channels (effective width about 3.5 Å in the widest channel) cross the double silicate layer. They show specific “octahedral” O layers that are discussed with particular reference to delhayelite and hydrodelhayelite. TR03 can be considered a Na-bearing hydrodelhayelite; this extra cation resides in the O layer and connects two edge-sharing rows of Ca-octahedra that, instead, are isolated in hydrodelhayelite. A further increase of the number of cations pfu leads to a fully occupied O layer, as found in delhayelite and TR04. The H2O molecules are hosted both in the channels and in the O layer; bond lengths and Raman spectra show that they are loosely hydrogen bonded. The structural features that support the wide range of chemical compositions found in the rhodesite series are discussed.

You do not currently have access to this article.