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

Abstract

Abstract Here, we show that in a supramolecular system with more than 20 building blocks forming large icosahedral M 12 L 8 metal–organic cages (MOCs), using the instant synthesis method, it is possible to kinetically trap and control the formation of interlocking M 12 L 8 nanocages, giving rare M 12 L 8 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 M 12 L 8 poly-[n]-catenane single crystal X-ray diffraction (SC-XRD) structure including nitrobenzene (1) indicates strong guest binding with the large M 12 L 8 cage (i.e., internal volume ca. 2600 Å3), allowing its structural resolution. Conversely, slow self-assembly (5 days) leads to a mixture of the M 12 L 8 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 M 12 L 8 poly-[n]-catenane (a1′), but not coordination polymers, selectively in 15 min. The dynamic behavior of the M 12 L 8 poly-[n]-catenanes demonstrated by the amorphous-to-crystalline transformation upon the uptake of ortho-, meta- and para-xylenes shows the potential of M 12 L 8 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 M 12 L 8 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 M 12 L 8 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.