Guest binding is governed by multiple stimuli in low-symmetry metal-organic cages containing bis-pyridyl(imine) vertices

Abstract

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^II₁₂L₈ (M = Zn^II and Co^II) pseudo-cuboctahedral architecture 1 and a rarer M^II₉L₈ (M = Zn^II and Co^II) pseudo-Johnson-solid-type (J₅₁) 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-methylcalix[4]resorcinarene, 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.