Microporous Solid Traps Alkanes

A new type of designed material containing pores lined with methyl groups has been shown by Fran??ois P. Gabba?? and his research group at Texas A&M University to reversibly adsorb simple alkanes at room temperature (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200602440). The materials could become the basis of a class of materials useful for separating or storing volatile hydrocarbons, the researchers note.

Materials with columnar pore structures that can trap alkanes have been made before, Gabbaï adds, but the pores of those materials typically are lined with aromatic groups. The methyl-lined material, which appears to be the first microporous solid with an alkylated interior, traps hydrocarbons by strong van der Waals attractions, the researchers believe.

Gabbaï and coworkers Thomas J. Taylor and Vladimir I. Bakhmutov made the material by mixing a tris(alkynyl)benzene compound, [(CH₃)₃SiCC]₃C₆H₃, with a trimeric perfluorophenylene-mercury complex, (HgC₆F₄)₃. These molecules aggregate into extended stacks via interactions of the mercury atoms with the benzene ring and CC bonds of the alkynyl compound to form a honeycomb structure with the silyl methyl groups pointing into the pores.

The team measured adsorption and desorption rates for alkanes ranging from methyl to n-hexane, with n-butane reaching the highest uptake of 2.9 wt % of the microporous solid. The alkanes can be desorbed under vacuum without any structural changes to the starting material.

The Texas researchers have "cleverly engineered" a microporous crystalline solid lined with trimethylsilyl groups, comments Jerry L. Atwood of the University of Missouri, Columbia. "The remarkable, versatile ability of these new materials to sorb alkanes is an exciting development. Although sorptive capacity is low with this generation of sorbents, applications in gas separation may well be developed."