Transformations in Chemically Responsive Copper-Calixarene Architectures

Self-assembly of bis-picolyl-appended calix[4]arene (L) with Cu^I or Cu^II salts resulted in a collection of multinuclear architectures capable of expressing structural reconfigurations in response to various chemical stimuli: addition of copper salt, solvents, or oxidation. Coordination of L to CuX (X=Br, I) selectively yielded dinuclear macrocycles Cu^I₂ L₂ Br₂ (1) and Cu^I₂ L₂ I₂ (3) that were transformed into tetranuclear assemblies Cu^I₄ L₂ Br₄ (2) and Cu^I₄ L₂ I₄ (4) upon further addition of CuX. These supramolecules persist as robust and discrete entities in solution that display red emission; notably, 4 exhibits luminescence thermochromism. Assembly of L with CuCl₂ produced macrocycle Cu^II₂ L₂ Cl₄ (5), which crystallised as cage [Cu^II₂ L₄ (μ-Cl)]³⁺ (6) in the presence of MeOH. Two chemical signals-introduction of CuCl₂ and addition of CH₃ CN-regenerated macrocycle 5. Coordination of L to Cu(OTf) yielded macrocycle Cu^I₂ L₂ (OTf)₂ (7) that also crystallised as cage 6 upon oxidation in CHCl₃ .