Most molecular materials don’t conduct electricity well because the electrons in them can’t travel around easily. Materials that do conduct have pathways for their electrons, formed by overlapping atomic orbitals–the space where electrons usually stay–between molecules. In order to increase the conductivity of a molecular crystal, Nickel 5,6-dihydro-1,4-dithiin-2,3-dithiolate, we used high pressure to squeeze the molecules together.
This work was an international collaboration with some really talented scientists in the RIKEN institute, Japan, Kumamoto University, Japan, and Diamond Light Source synchrotron, UK.
Hengbo and Reizo at RIKEN made the molecular crystals and measured their conductivity under high pressure. They did this by attaching tiny wires to the crystal inside a Diamond Anvil Cell (DAC)–a device that generates pressure larger than found at the bottom of the ocean. They found that, whilst normally the crystal didn’t conduct electricity at all, when it was squeezed its conductivity increased dramatically.
In order to understand why, we used X-ray diffraction to work out the crystal structure–where the atoms are and how they are bonded together. Aided by Chloe and Mark, we fired intense X-ray beams produced at Diamond Light Source through our crystal in the DAC and measure how they scattered. From the scattering, we could show for the first time that the molecules got closer and closer together under pressure.
The final piece in the puzzle came from Takao at Kumamoto, who used theoretical calculations based on the X-ray crystal structures to work out the changes in orbital interactions. And the calculations showed that the orbitals between the molecules indeed overlapped more and more with pressure, explaining why the crystals’ conductivity got higher.
A link to the paper can be found here. It’s Open Access, meaning anyone can read it for free!
Thanks and well done to Hengbo, Takao, Chloe, Reizo and Mark!
Yeung Research Group at UoB 