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 Ci 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.
Highlights
Scheme 1 Dianin's compound and structural variants
The first indication that this packing might not, represent a unique clathrate potential energy minimum came from the reported unit cell dimensions[10] of the EtOH clathrate of 3, which showed relative to the expected dimensions, c essentially remained unchanged but a effectively doubled with a = 57.42(1) Å and c = 10.871(1) Å; all attempts to solve this structure were unsuccessful owing to the fact that only X-ray photographic data were available at that time
In 2009 Jacobs and co-workers[14] published the structure of the ethylenediamine clathrate of compound 1 which interestingly demonstrated a unit cell which was doubled in a relative to the archetypal Dianin's cell which contained two distinct unit types wherein one unit contained neutral guest molecules and the second contained partially ionised guests
Summary
Scheme 1 Dianin's compound and structural variants. PaperCrystEngComm form isomorphous, not in all cases isostructural, host lattices which are analogous to those of 1 and 2, invariably with Z′(host) = 1.
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