Intrazeolitic chemistry creates new molecules

For the past several decades, Karl Seff of the University of Hawaii and his coworkers have been conducting intrazeolitic chemistry in which they use X-ray crystallography to watch what happens inside the tiny pores of zeolites as they are heated or chemically treated. Put another way, Seff says, “it’s doing chemistry in a 1-nm test tube.” The research has paid off with observations that could be helpful in understanding how the industrially important catalysts and sorbents work, as well as with the discovery of a few unexpected new molecules (J. Phys. Chem. C 2016, DOI: 10.1021/acs.jpcc.5b11490). The Seff team’s work has centered on the synthetic sodium aluminosilicates known as zeolites A and X in which some sodium ions are replaced by silver ions. In one observation, the researchers noticed that the crystallinity of the material waxes and wanes depending on the dynamics of oxygen atoms in the zeolite framework and the presence of O₂. Furthermore, the team observed formation of quantum-dot-like silver halide clusters and octahedral Ag₆ clusters within the pores under various conditions. Seff notes that Ag₆ is the smallest possible single crystal of silver that can form. When passing ammonia through the silver-exchanged zeolites, the researchers observed formation of unprecedented bent N₃H₅ and cyclic N₃H₃. And with methanol, they saw cyclic C₃H₃O₃³⁺—a new molecule that is electronically equivalent to benzene. Seff cautions that this menagerie of molecules may only be spotted within the pores of zeolites and be impossible to isolate outside those confines.