Hexahomotrioxacalix[3]arenes, commonly called oxacalix[3]arenes, were first reported in 1962. Since then, their chemistry has been expanded to include numerous derivatives and complexes. This review describes the syntheses of the parent compounds, their derivatives, and their complexation behaviour towards cations. Extraction data are presented, as are crystal structures of the macrocycles and their complexes with guest species. Applications in fields as diverse as ion selective electrode modifiers, fluorescence sensors, fullerene separations and biomimetic chemistry are described.

The binding properties of the tetra(diethyl)amide (2) derived from p-tert-butyldihomooxacalix[4]arene, in the cone conformation, towards alkali, alkaline earth, transition (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) and heavy (Ag⁺, Cd²⁺, Hg²⁺ and Pb²⁺) metal cations have been established by extraction studies of metal picrates from an aqueous solution into dichloromethane, transport experiments with the same salts through a dichloromethane membrane and stability constant measurements in methanol. Results concerning the calorimetric study of Na⁺ and K⁺ complexes in methanol are presented. The affinity of 2 for some cations (Na⁺, K⁺, Ba²⁺, Ag⁺ and Zn²⁺) has been investigated by ¹H NMR spectrometry, as well. The results are compared to those obtained with the analogous calix[4]arene tetraamide derivative 3. Amide 2 displays a preference for the alkali cations (mainly Na⁺ and K⁺) in contrast to amide 3 that prefers the alkaline earth cations. Ag⁺ and Cd²⁺ soft Lewis acids are also strongly bound by both amides. ¹H NMR titrations confirm the formation of 1∶1 complexes between 2 and all cations studied, also suggesting that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. 2 shows transport rates that do not follow the same trends as the stability constants or extraction percentages; it can therefore be characterized as a selective receptor.