Participation of Xenon Guest in Hydrogen Bond Network of β-Hydroquinone Crystal

In the beta-hydroquinone (beta-HQ)-Xe crystal, the Xe guest is placed between two hexagonal rings of coupled [center dot center dot center dot O-H center dot center dot center dot 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 [center dot center dot center dot O-H center dot center dot center dot O-](6) bonds are considered: (i) structural changes in the clathrate (X-ray diffraction), (ii) variations of Xe-129 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 [center dot center dot center dot O-H center dot center dot center dot O-](6) rings into the Xe atom and formation of six Xe center dot center dot center dot H-O pairs in every cage, the frequency shift of the gamma OH mode due to these contacts, -Delta gamma OH(Xe center dot center dot center dot H) > 74 cm(-1), as well as the enthalpy formation, -Delta H(Xe center dot center dot center dot 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 center dot center dot center dot D-O interactions in the H/D substituted crystal. The Xe-129 NMR results do not reflect this kind of interactions due to averaging of the Xe-129 shielding phenomena, probably. We also predict elongation of the O center dot center dot center dot O distances due to the beta-HQ-Xe crystal heating and the Xe escape.