An unprecedented Dianin clathrate structure with Z′(host) = 16

Abstract

The structure of the iso-propanol clathrate of 4-p-hydroxyphenyl 2,2,4-trimethylthiachroman, the direct thia-analogue of Dianin's compound, has been studied by single-crystal X-ray diffraction as a function of temperature from 371 K down to 90 K. The standard Dianin unit cell, observed at high temperature, undergoes two sequential commensurate thermal phase transformations which results at low temperature in a unit cell with 16 times the original volume and with Z′(host) = 16 and Z = 288, the space group R being retained. This ultimate unit cell with a quadrupled a-axis has a = 111.7910(5) Å and c = 10.8568(1) Å and the crystal packing now features not only the prototypal [OH]₆ hexamer host unit but also novel hydrogen-bonded octameric host–guest units with respective symmetries C_i and C₁. In addition it has been established that the corresponding achiral selena-Dianin's clathrate and the polar chiral quasiracemic iso-propanol clathrate, space group R3, formed from R-Dianin's and S-thia-Dianin's components also exhibit novel related temperature-dependant behaviour.