Static disorder of dodecasil 3C. A single-crystal study with synchrotron radiation

New silica clathrate minerals that are isostructural with natural gas hydrates

“…At high temperatures, the space groups of melanophlogite and MTN-type clathrasil have the highest symmetries of Pm3 _ n and Fd3 _ m, respectively 29,30 . They undergo symmetry-lowering on distortion of the frameworks with a decrease in temperature or an increase in pressure 26,29,31 .…”

The Cubic/Tetragonal Phase Transition in D3C–THF: an Optical and X-ray Powder Diffraction Study

“…According to Salje (15), for the excess volume strain T all coupling terms KQL with m"1 and n the exponents in Eq. [5] are symmetry-allowed.…”

“…In D3C all-corner-connected SiO tetrahedra from pentagon-dodecahedra cages (face symbol [5]), which are face-connected in such a way that they build pseudohexagonal nets. A cubic close packing of these nets results in a second kind of cage, the hexadecahedra (face symbol [56]).…”

“…Structure-directing template molecules such as pyridine or trimethylamine are located in the [56] cages, whereas smaller molecules like CH and atoms like Kr, Xe, and Ar are usually located in the [5] cages. For the title compound, the template is tetrahydrofurane, (CH ) O (THF for short), which is located in the hexadecahedra cages.…”

“…The space group Fd3 m has been given for detemplated D3C (5). For the guest molecule pyridine, the D3C structure was described in the tetragonal space group I4 2d (6), whereas for pyrrolidine Fddd (8) and for tert-butylamine I4 /a (8) have been determined.…”