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In the β-hydroquinone (β-HQ)-Xe crystal, the Xe guest is placed between two hexagonal rings of coupled [···O-H···O-](6) H-bonds. This clathrate is treated as the model for monitoring the H-bonding system with the Xe participation. Three kinds of isotope effects due to the H/D substitution in the [···O-H···O-](6) bonds are considered: (i) structural changes in the clathrate (X-ray diffraction), (ii) variations of (129)Xe NMR signal of the guest (CP MAS), and (iii) variations of selected vibrations of the host (IR). This study predicts subtle inclination of every other hydroxyl group of the [···O-H···O-](6) rings into the Xe atom and formation of six Xe···H-O pairs in every cage, the frequency shift of the γOH mode due to these contacts, -ΔγOH(Xe···H) > 74 cm(-1), as well as the enthalpy formation, -ΔH(Xe···H) > 6-8 kJ mol(-1). Our IR results reveal a tendency of the Xe atom to form the H-bond-like network inside its cage and much weaker Xe···D-O interactions in the H/D substituted crystal. The (129)Xe NMR results do not reflect this kind of interactions due to averaging of the (129)Xe shielding phenomena, probably. We also predict elongation of the O···O distances due to the β-HQ-Xe crystal heating and the Xe escape.

Up to now, three brucine hydrates are known, brucine di-, tetra-, and 5.25-hydrate. All of them were obtained from solutions containing the additive diethanolamine, adenosine, and urea, respectively. Studying the role of the additives on crystallization of the brucine hydrates, we obtained a new, kinetically favored brucine 3.86-hydrate. In crystals of brucine 3.86-hydrate, large 15- and 16-membered water clusters of cuboidal topology are encapsulated in cages formed between honeycomb-like brucine layers. Dehydration of the brucine hydrate leads to formation of the known anhydrous brucine, giving insight into a mechanism of the dehydration process, in which a shift of brucine ribbons in the honeycomb-like layers leads to an openining of channels and water release. A collapse of brucine layers after the water release results in formation of the common anhydrous brucine. The anhydrous brucine undergoes a phase transition at 249 K in the cooling mode and at 277 K in the heating mode. The phase transition is attributable to a huge shift of brucine corrugated layers in relation to each other. The phase transition for anhydrous brucine obtained by dehydration is accompanied by thermal effects one order larger than anhydrous brucine, obtained by crystallization from acetone solution.

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