The monolayer structure of 1,2-bis(4-pyridyl)ethylene physisorbed on a graphite surface

Abstract

The crystalline monolayer of 1,2-bis(4-pyridyl)ethylene physisorbed on a graphite surface at 0.44 monolayers coverage has been observed and characterized by synchrotron X-ray diffraction and differential scanning calorimetry. The experimentally determined monolayer structure has p2 symmetry with lattice parameters a = 17.77 Å, b = 13.69 Å and ν = 39.7°. The unit cell contains two molecules, which are oriented in a plane parallel to the surface. It is proposed that the molecules are arranged such that they are able to form a weak C–H ··· N hydrogen bond between pyridine groups. The monolayer melts at 414 K, which is unusually close to the bulk melting point for a sub-monolayer coverage system. This molecule is chiral when adsorbed on the surface, but both isomers appear in the unit cell leading to no overall chirality in the monolayer.

Keywords:

• monolayer
• synchrotron
• physisorption
• 1,2-bis(4-pyridyl)ethylene
• graphite

Acknowledgements

We thank the BP Institute, Diamond Light Source and the University of Cambridge for financial support and facilities. Thanks also go to Chiu Tang, Stephen Thompson and the other staff at DLS for beam time and technical support, and to Bob Thomas for helpful discussions. AYB would like to acknowledge EPSRC for funding. The Herchel Smith fund is acknowledged for a research fellowship (TF). This work was carried out with the support of the Diamond Light Source.