CENTC researchers find gases react inside single crystals

A newly synthesized family of molecular single crystals has two remarkable capabilities, reported in this week's Nature by CENTC researchers Prof. Maurice Brookhart (Univ. Of North Carolina) and graduate student Zheng Huang (now a post-doctoral fellow at Univ. Of Illinois, Urbana-Champaign). Members of the molecular family can exchange small gaseous ligands for others, while retaining their integrity as single crystals; and some of the family members can act as selective catalysts for the hydrogenation of ethylene gas.
Maurice Brookhart and colleagues synthesized an organometallic compound, [Ir]-N₂, in which a reactive iridium atom, supported by an organic 'pincer' ligand, binds a nitrogen molecule. Crystallizing this compound from a toluene solution yields single crystals, in which the [Ir]-N₂ molecules are stacked around channels containing toluene molecules.

Exposing the [Ir]-N₂ crystals to other small-molecule gases, such as carbon monoxide, ammonia or ethylene, results in solid-state transformations to analogous compounds in which each of these gases replaces nitrogen. The authors show that these transformations take place by direct exchange reactions inside the intact crystals, rather than by ligand loss followed by uptake. The gaseous ligands evidently enter the crystals via the toluene-containing channels, which exclude entry by all but the smallest molecules.

Three of the compounds also function as hydrogenation catalysts for ethylene and propylene, with a strong selectivity for the smaller gas when reactions are prevented from occurring at or near the crystal surfaces. This appears to be the first demonstration of a selective catalytic reaction occurring inside an organometallic crystal.

Read the full article: Huang, Z.; White, P. S.; Brookhart, M. “Ligand Exchanges and Selective Catalytic Hydrogenation in Molecular Single Crystals”, Nature, 2010, 465, 598-601.
DOI: http://dx.doi.org/10.1038/nature09085