Isostructural synthesis of porous metal-organic nanotubes.

Employment of semirigid double-hinged di-1,2,4-triazoles has led to the synthesis of an isostructural series of metal-organic nanotubes (MONTs). The ditriazole ligands adopt a syn conformation between rigid metal chains while an appropriate anion choice provides a "capping" of the metal ions, leading to MONT formation. This approach of utilizing a variety of both semirigid ligands and metals is the first general methodology to prepare this class of 1D nanomaterial. The local geometry at the metal center depends on the metal ion employed, with Cu(I) centers adopting a tetrahedral geometry, Ag(I) centers adopting a seesaw geometry, and Cu(II) centers adopting a square-pyramidal geometry upon MONT synthesis. The pore size of the MONTs is adjusted by changing the central portion of the double-hinged ligand, allowing for a predictable method to control the pore width of the MONT. The adsorption properties of MONTs as a function of pore size revealed selective uptake of CO2 and CH4, with copper MONTs exhibiting the highest uptake. In the case of the silver MONTs, an increase in pore width improves both gas uptake and selectivity.