When atoms combine to form compounds, they must follow certain bonding and valence rules. For this reason, many compounds simply cannot exist. But there are some compounds that, although they follow the bonding and valence rules, still are thought to not exist because they have unstable structures. Scientists call these compounds "impossible compounds." Nevertheless, some of these impossible compounds have actually been fabricated (for example, single sheets of graphene were once considered impossible compounds). In a new study, scientists have synthesized another one of these impossible compounds -- periodic mesoporous hydridosilica -- which can transform into a photoluminescent material at high temperatures.
The researchers, led by Professor Geoffrey Ozin of the Chemistry Department at the University of Toronto, along with coauthors from institutions in Canada, China, Turkey, and Germany, have published their study in a recent issue of the Journal of the American Chemical Society.
Like graphene, periodic mesoporous hydridosilica (meso-HSiO1.5) consists of a honeycomb-like lattice structure. Theoretically, the structure should be so thermodynamically unstable that the mesopores (the holes in the honeycomb) should immediately collapse into a denser form, HSiO1.5, upon the removal of the template on which the material was synthesized.
In their study, the researchers synthesized the mesoporous material on an aqueous acid-catalyzed template. When they removed the template, they discovered that the impossible material remains stable up to 300 °C. The researchers attribute the stability to hydrogen bonding effects and steric effects, the latter of which are related to the distance between atoms. Together, these effects contribute to the material’s mechanical stability by making the mesopores resistant to collapse upon removal of the template.
“The prevailing view for more than 50 years in the massive field of micro-, meso-, or macroporous materials is that a four-coordinate, three-connected open framework material (called disrupted frameworks) should be thermodynamically unstable with respect to collapse of the porosity and therefore should not exist,” Ozin told PhysOrg.com. ...
via Chemists fabricate 'impossible' material.