Pseudo-polymorphism of a camphor α-cyclodextrin complex

Crystalline products of vapor diffusion of an alcoholic solution of 1R ,4R-camphor into an aqueous solution of alpha-cyclodextrin were prepared and subjected to X-ray structure analysis. Two different forms were obtained: a dimeric cavity formed by head-to-head association of cyclodextrin (phase A), and a complex set of monomeric cavities (phase B). Both contain camphor molecules orientationally disordered inside cavities. The structures are solvated by mixtures of water and ethanol. The structures significantly differ in chemical stabilities. Whilst phase A is relatively stable with respect to guest desorption, phase B rapidly reacts to change of its chemical envi-ronment manifested by cracking of crystals in solution. The phenomenon has been recorded and a short movie is included in the supplementary data.

Automated summary

Crystalline products of 1R, 4R-camphor vapor diffusion into an aqueous solution of alpha-cyclodextrin were prepared and analyzed by X-ray structure analysis. Two different forms, a dimeric cavity (phase A) and a complex set of monomeric cavities (phase B), were obtained. Both structures contained camphor molecules that were disordered. Additionally, the structures were solvated by mixtures of water and ethanol. The chemical stabilities of the two structures differed significantly, with phase A being relatively stable and phase B reacting rapidly to changes in its chemical environment, leading to cracking of crystals in solution.