Bottom-up realization of a porous metal-organic nanotubular assembly

Nanotubes are generally prepared from their constituent elements at high temperatures, and thus it is difficult to control their size, shape and electronic states. One useful approach for synthesizing well-defined nanostructures involves the use of building blocks such as metal ions and organic molecules. Here, we show the successful creation of an assembly of infinite square prism-shaped metal-organic nanotubes obtained from the simple polymerization of a square-shaped metal-organic frame. The constituent nanotube has a one-dimensional (1D) channel with a window size of 5.9×5.9 Å2, and can adsorb water (H2O) and alcohol vapours, whereas N2 and CO2 do not adhere. It consists of four 1D covalent chains that constitute a unique electronic structure of 'charge-density wave (CDW) quartets' on crystallization. Moreover, exchanging structural components and guest molecules enables us to control its semiconductive bandgap. These findings demonstrate the possibility of bottom-up construction of new porous nanotubes, where their degrees of freedom in both pore space and framework can be used.