Conformational Control of Oxacalix[3]arene[3]triazine with Anion-π Interactions

Oxacalix[3]arene[3]triazine 1 bearing three electron-deficient triazine rings was designed as a molecular model to probe the effect of anion complexation on the conformation. Owing to the intrinsic nature of bridging oxygen atoms, the flexibility arising from the six aromatic units in the macrocycle, and unique intermolecular interactions, 1 gave a tight-waisted 1,3,5-alternate conformation in the solid state. Dramatic conformational changes of 1 after binding with halide anions were revealed by X-ray crystallography. The 1:3 complexation of 1 and chloride ([1 center dot 3Cl(-)]) led to a pyramidal conformation as a result of cooperative anion-pi interaction and weak hydrogen bonding. In contrast, 1 binding with two bromides forms a 1:2 complex, and the conformation of macrocycle produced is a C-3-symmetric 1,3,5-alternate one.