Self-assembly and host-guest chemistry of a 3.5-nm coordination nanotube

Upon complexation with Pd(II) ions, precisely designed strandlike ligands with two tris(3,5-pyridine) units at both terminals were assembled, with the aid of a linear template molecule, into a discrete tubular complex with a length of 3.5 nm. The high stability and the well-defined structure of the coordination nanotube were revealed by NMR spectroscopy, cold-spray ionization MS, and single-crystal X-ray analysis. Guest lengths were discriminated by the tube: When the association of strandlike guest molecules, in which two biphenylene units are linked with an (OCH2CH2)n linker, were compared, the tube selectively recognized an appropriate guest whose length was comparable to that of the tube. Tetrathiafulvalene (TTF)-terminated linear guests were directly oxidized to TTF2+ in the tube, but reduced stepwise via TTF+ outside the tube.