Anion-directed assembly of a rectangular supramolecular cage in the solid state with electron-deficient phenoxylated oxacalix[2]arene[2]triazinew

Anion receptors bearing p electron-deficient arenes have attracted increasing interest during the past decade. The anion–p interaction between charge neutral electron-deficient aromatic rings, as predicted by theoreticians, has been evidenced experimentally both by solid state and solution investigations. For example, in the solid state, while weaks-interaction in which anions interact with p electron-deficient arenes such as, tetracyanobenzene, tetracyanopyrazine and 1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile, from the periphery of the aromatic rings has been shown, typical anion–p interaction in which an anion (halide) is located just over the triazine centroid of a macrocyclic oxacalix[2]arene[2]triazine host molecule has been observed. Despite the increasing number of examples of anion–p interactions being reported in the literature, it is worth addressing that as an emerging catalog of non-covalent bond interaction, the directing ability of anion–p interaction to induce the molecular assembly based on charge neutral electron deficient arenes has rarely been studied. As one of the typical macrocyclic molecules of heteracalixaromatics, a new generation of host molecules in supramolecular chemistry, the 1,3-alternate conformational oxacalix[2]arene[2]triazines have been shown to use their electron-deficient V-shaped cleft to interact with anions through anion–p interactions. Our previous study has demonstrated that the binding ability of tetraoxacalix[2]arene[2]triazines towards anions was affected remarkably by the electronic nature of the substituents on triazine rings. In other words, the anion–p interaction of triazine toward anions was regulated by the substituents. We have also demonstrated that anion–p interaction along with hydrogen bonds led to interesting self-assembled structures in the solid state. Our interest in directing the effect of anion–p interactions on molecular self-assembly has led us to the current study. To fine-tune the anion–p binding ability of triazine rings, and also to append potential p–p stacking moieties, phenoxy and perfluorophenoxy substituents are introduced into triazine rings of oxacalix[2]arene[2]triazine. We were delighted to find out that chloride–p interaction along with lone-pair electron–p interaction, hydrogen bonding and p–p stacking induced the hexameric assembly of the parent macrocycle into a rectangular supramolecular cage in the solid state. To synthesize the target macrocyclic molecules, we first carried out aromatic nucleophilic substitution reaction starting from parent dichloro-substituted oxacalix[2]arene[2]triazine 1 with pentafluorophenol 2 and phenol. The reaction between 1 and 2 proceeded efficiently in the presence of K2CO3 in acetonitrile at room temperature, giving 5b almost quantitatively. However, similar reaction using phenol as a nucleophilic agent yielded unfortunately a trace amount of desired product 5a. A one-pot protocol with resorcinol 3 and 2,4-dichloro-6phenoxy-1,3,5-triazine 4 (see ESIw for synthesis of 4) as the starting materials was then employed, which gave successfully 5a in 39% yield (Scheme 1). The structures of all the synthesized compounds were established on the basis of their spectroscopic data and microanalysis