Crystal structure of theβ-clathrate form of 4-p-hydroxyphenyl-2,2,4-trimethylselenachroman

Abstract

In contrast top-hydroxyphenyl-2,2,4-trimethylchroman, Dianin's compound (1), or itsthia analogue2, the title seleno-ether has been found to form two crystallographically distinct types of clathrate. In the first-discovered form, the α-modification of as yet undefined structure, the rhombohedral unit cell (R$\bar 3$, a = 57.42(1) Å, c = 10.817(1) Å, [from EtOH]) has approximately four times the volume of that found in the clathrates of1 or2 and contains 72 host molecules. Recrystallisation of the selena-host fromn-hexane, however, produces another type of rhombohedral crystal: theβ-modification has space group R$\bar 3$, witha=28.225(2)Å,c=10.859(1)Å, and 18 host molecules in the unit cell. A detailed X-ray study of this latter inclusion compound (host-guest ratio 6:1) has established its true clathrate nature; the disorderedn-hexane guest, showing electron density consistent with an extended planar zig-zag conformation, is found threading the hour glass-shaped cavity's central constriction.