The structure, they found, confirmed theories based on chemical analyses. For example, the barbell-shaped hydrogen molecule snuggles into the catalyst core. On being split, the negatively charged hydride attaches to the iron at the center of the catalyst; meanwhile, the positively charged proton attaches to a nitrogen atom across the catalytic core. The researchers expected this set-up, but no one had accurately characterized it in an actual structure before.
In this form, the hydride and proton form a type of bond uncommonly seen by scientists -- a dihydrogen bond. The energy-rich chemical bond between two hydrogen atoms in a molecule is called a covalent bond and is very strong. Another bond called a "hydrogen bond" is a weak one formed between a slightly positive hydrogen and another, slightly negative atom.
Hydrogen bonds stabilize the structure of molecules by tacking down chains as they fold over within a molecule or between two independent molecules. Hydrogen bonds are also key to water surface tension, ice's ability to float and even a snowflake's shape.
The dihydrogen bond seen in the structure is much stronger than a single hydrogen bond. Measuring the distance between atoms reveals how tight the bond is. The team found that the dihydrogen bond was much shorter than typical hydrogen bonds but longer than typical covalent bonds. In fact, the dihydrogen bond is the shortest of its type so far identified, the researchers report.
This unusually strong dihydrogen bond likely plays into how well the catalyst balances tearing the hydrogen molecule apart and putting it back together. This balance allows the catalyst to work efficiently.
"We're not too far from acceptable with its efficiency," said Bullock. "Now we just want to make it a little more efficient and f
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory