"We were studying agostic bonds ... " said the chemist. ... While chemists have studied these bonds in chemicals in liquid form, no one had crystallized one chemical with multiple forms of its agostic bonds. And no one expected different forms to give rise to different colors.
Bonds come in many varieties in molecules. They string atoms together, sometimes forming a trunk and branches of atoms like a tree. But the trunk and branches of chemicals often fold up into a more compact shape, requiring additional weaker bonds to hold the shape in place. An agostic bond is one of these additional bonds, a shape-holder. They occur between a metal and a distant carbon-hydrogen bond along some chain, folding the chain back to the metal and pinning it there.
In the lab, the researcher's flask of chemicals held a molybdenum-containing molecule that turned the solution violet. The researcher added another liquid to coax the molybdenum complex to crystallize, just as salt crystallizes from seawater to form flakes at the seashore. Some crystals formed at the bottom of the flask and others formed near the top of the violet solution.
Oddly, the crystals were two different colors.
Orange crystals formed at the bottom of the flask and blue above. If the reseasrcher dissolved either the orange or blue crystals in a fresh flask of the original solvent, the violet color returned, with the same properties as the original violet solution.
Bron, lees meer:
E. F. van der Eide, et al.: Isolation of Two Agostic Isomers of an Organometallic Cation: Different Structures and Colors
Veranderd door confusie, 07 augustus 2013 - 18:41