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Inspired by natural systems, metal-organic cages with well-defined shapes and cavities can be tuned for different guest-binding functions. Here, we report the construction of two types of cage frameworks: an M II 12 L 8 (M = Zn II and Co II ) pseudo -cuboctahedral architecture 1 and a rarer M II 9 L 8 (M = Zn II and Co II ) pseudo -Johnson-solid-type ( J 51 ) framework 2 . Both structures form from the same boron-containing triamine subcomponent, and each one incorporates hexacoordinate metal vertices chelated by only two bidentate pyridyl(imine) arms. Such vertices provide the cages with the flexibility required to form lower-symmetry architectures, and they also facilitate reversible disassembly in response to fluoride. These cages were also shown to respond to other chemical stimuli enabling transformation between cage structures. Cage 1 bound different guest molecules, including the anticancer drug paclitaxel, C -methylcalix4resorcinarene, and tetraphenylborates. The release of paclitaxel by 1 was stimulated by fluoride or chloride, highlighting the potential for applications in natural product separation and drug delivery.
Yang et al. (Fri,) studied this question.