Transitions in Solvate Crystals of a Tetraaryladamantane

Abstract

Obtaining high‐resolution structures of liquid compounds can be difficult. Encapsulating them in the lattice of a larger organic molecule acting as crystallization chaperone is one option to overcome this difficulty. Tetraaryladamantane ethers can play the role of chaperones, accommodating a range of different guest molecules in their crystals. How well ordered crystalline arrangements for molecules of different shape are achieved is not clear. Cases in which more than one structure is found may shed light on this phenomenon. Here we report low order cubic crystal structures of 1,3,5,7‐tetrakis(2,4‐dimethoxyphenyl)adamantane (TDA) encapsulating ortho‐xylene or cyclohexane, together with better ordered structures obtained after warming the crystals to 60 °C. Evidence for cubic crystal systems was also found for limonene, hexachlorobutadiene and eucalyptol, with a transition to a triclinic system for the former two, but no transition up to 70 °C for the latter. These findings indicate that some solvate structures of TDA can readily undergo structural transitions to less solvated, better ordered systems. Crystals obtained by rapid thermal crystallization may be kinetically trapped states, and the transition to a solvate‐free crystal system appears to have a kinetic barrier that depends strongly on the structure of the liquid guest molecules encapsulated in the lattice.

A Fluorinated Chaperone Gives X‐ray Crystal Structures of Acyclic Natural Product Derivatives up to 338 Molecular Weight

“…200 °C below the mp of the chaperone, as for compounds like TDA and TEO. [20,22] This may give the molecules involved the ability to undergo translational and rotational movements required to find their positions in the crystal lattice before they are frozen in place. Finally, the fluoro substituent of TFM is smaller than the bromo substituent of TBro, another factor that may favor the encapsulation of larger analytes.…”

“…These are 1,3,5,7-tetrakis(2,4-dimethoxyphenyl)adamantane (TDA), [20,21] 1,3,5,7-tetrakis(2,4diethoxyphenyl)adamantane (TEO) [22] and 1,3,5,7-tetrakis(2bromo-4-methoxyphenyl)adamantane (TBro). [15] All three have specific advantages, such as ease of use, as no solvent screening is required for crystallization, and small quantities of just a few milligrams required for crystallization, but the known TAAs also have drawbacks.…”