Kinetic trapping of 2,4,6-tris(4-pyridyl)benzene and ZnI₂ into M₁₂L₈ poly-[n]-catenanes using solution and...

Here, we show that in a supramolecular system with more than 20 building blocks forming large icosahedral M₁₂L₈ metal-organic cages (MOCs), using the instant synthesis method, it is possible to kinetically trap and control the formation of interlocking M₁₂L₈ nanocages, giving rare M₁₂L₈ TPB-ZnI₂ poly-[n]-catenane. The catenanes are obtained in a one-pot reaction, selectively as amorphous (a1) or crystalline states, as demonstrated by powder X-ray diffraction (powder XRD), thermogravimetric (TG) analysis and ¹H NMR. The 300 K M₁₂L₈ poly-[n]-catenane single crystal X-ray diffraction (SC-XRD) structure including nitrobenzene (1) indicates strong guest binding with the large M₁₂L₈ cage (i.e., internal volume ca. 2600 ų), allowing its structural resolution. Conversely, slow self-assembly (5 days) leads to a mixture of the M₁₂L₈ poly-[n]-catenane and a new TPB-ZnI₂ (2) coordination polymer (i.e., thermodynamic product), as revealed by SC-XRD. The neat grinding solid-state synthesis also yields amorphous M₁₂L₈ poly-[n]-catenane (a1'), but not coordination polymers, selectively in 15 min. The dynamic behavior of the M₁₂L₈ poly-[n]-catenanes demonstrated by the amorphous-to-crystalline transformation upon the uptake of ortho-, meta- and para-xylenes shows the potential of M₁₂L₈ poly-[n]-catenanes as functional materials in molecular separation. Finally, combining SC-XRD of 1 and DFT calculations specific for the solid-state, the role of the guests in the stability of the 1D chains of M₁₂L₈ nanocages is reported. Energy interactions such as interaction energies (E), lattice energies (E*), host-guest energies (E_host-guest) and guest-guest energies (E_guest-guest) were analysed considering the X-ray structure with and without the nitrobenzene guest. Not only the synthetic control achieved in the synthesis of the M₁₂L₈ MOCs but also their dynamic behavior either in the crystalline or amorphous phase are sufficient to raise scientific interest in areas ranging from fundamental to applied sides of chemistry and material sciences.