Jozef Hodyl PhD Thesis - Theses - Flinders University

contains two hydroxy groups in the ortho position, it would appear that more thanone such non-classical hydrogen bond is possible.As the relative magnitude of the binding constants, obtained in DMSO-d 6 , for thehydroxybenzoate guests is the inverse of those obtained in 20% aqueous dioxane, 129,166 and suggested by percent inclusion values obtained in H 2 O with the silica boundmacrocyclic receptor 94, 1 H NMR monitored titration experiments were alsoconducted with receptor 49 in CD 3 OD. This is a solvent with hydrogen bondacceptor and donor properties more closely related to those of H 2 O. It wasanticipated that in CD 3 OD the same trend as seen in 20% aqueous dioxane withreceptor 29 might be observed. However, as may be seen in Table 3.2 this was notthe case. It would appear that the presence of water is an essential criterion for thetrend observed with receptors 29 and 94 to occur.A speculative explanation for this phenomenon can be extracted from the crystalstructure of an o-hydroxybenzoate guest included in the cavity of ∆-[Cd(Sthpc12)](ClO4 ) 2.0.5H 2 O as shown in Figure 6.2. 97Figure 6.2 Crystal structure showing the interaction of an intramolecularly H-bonded o-hydroxybenzoate guest H-bonded to hydroxyl groups of ∆-[Cd(Sthpc12)](ClO4 ) 2.0.5H 2 O. H-bonds are in dashed lines. H atoms and perchlorate areomitted for clarity. O9 is the water molecule atom. 97100