Kinetic Trapping of 2,4,6-Tris(4-pyridyl)benzene and ZnI 2 into M 12 L 8 poly-[n]-catenanes using unconventional self-assembling processes

Abstract

Here we show that in a supramolecular system with more than 20 building blocks forming the 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 the rare M12L8 TPB-ZnI2 poly-[n]-catenane. The catenanes are obtained in one-pot reaction, selectively as amorphous (a1) or crystalline states as demonstrated by powder X-ray diffraction (powder XRD), thermogravimetrical (TG) analysis and 1H NMR. The 300 K M12L8 poly-[n]-catenane single crystal X-ray diffraction (SC-XRD) structure including nitrobenzene (1), indicates a strong guest binding with the large M12L8 cage (i.e., internal volume ca. 2700 Å3) allowing its structural resolution. Conversely, slow self-assembly (5 days) leads 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 the amorphous M12L8 poly-[n]-catenane (a2), but not coordination polymers, selectively in 15 mins. 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 are reported. Energy interactions such as interaction energies (E), the lattice energies (E*), the host-guest energies (Ehost-guest) and the guest-guest energies (Eguest-guest) have been analysed considering the X-ray structure with and without 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 the scientific interest in areas ranging from fundamental to the applied sides of chemistry and material sciences.