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 (Cu2L2Br2)-L-I (1) and (Cu2L2I2)-L-I (3) that were transformed into tetranuclear assemblies (Cu4L2Br4)-L-I (2) and (Cu4L2I4)-L-I (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 (Cu2L2Cl4)-L-II (5), which crystallised as cage [(Cu2L4)-L-II(-Cl)](3+) (6) in the presence of MeOH. Two chemical signalsintroduction of CuCl2 and addition of CH(3)CNregenerated macrocycle 5. Coordination of L to Cu(OTf) yielded macrocycle (Cu2L2)-L-I(OTf)(2) (7) that also crystallised as cage 6 upon oxidation in CHCl3.