Faculty of Chemistry, Wrocław University, 50-383 Wrocław, Joliot Curie 14, Poland.
J Phys Chem A. 2012 Mar 29;116(12):3206-14. doi: 10.1021/jp210670k. Epub 2012 Mar 16.
In the β-hydroquinone (β-HQ)-Xe crystal, the Xe guest is placed between two hexagonal rings of coupled ···O-H···O- 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- 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- 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.
在β-对苯二酚（β-HQ）-氙晶体中，氙客体位于两个耦合的[···O-H···O-]（6）氢键的六元环之间。该包合物被视为监测氙参与的氢键系统的模型。考虑了由于[···O-H···O-]（6）键中的 H/D 取代而产生的三种同位素效应：（i）包合物的结构变化（X 射线衍射），（ii）客体的（129）Xe NMR 信号的变化（CP MAS），以及（iii）主体的选定振动的变化（IR）。这项研究预测了[···O-H···O-]（6）环中每个羟基的微妙倾斜，以及每个笼中形成六个 Xe···H-O 对，由于这些接触导致γOH 模式的频率位移，-ΔγOH（Xe···H）>74cm-1，以及焓形成，-ΔH（Xe···H）>6-8kJmol-1。我们的 IR 结果表明氙原子在其笼内形成氢键样网络的趋势，以及在 H/D 取代晶体中氙···D-O 相互作用较弱。（129）Xe NMR 结果可能由于（129）Xe 屏蔽现象的平均化而不反映这种相互作用。我们还预测由于β-HQ-氙晶体加热和氙逸出，O···O 距离会延长。
