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

摘要

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 ?, b = 13.69 ? 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.