Hydrogen-Bond Nature Studied by X-ray and Neutron Structure Analyses of MeHPLN at Room Temperature

The hydrogen-bonded material, 5-methyl-9-hydroxyphenalenon (MeHPLN), was studied by X-ray and neutron diffraction experiments at room temperature in order to understand the hydrogen-bond nature and the relation between the hydrogen-bonds and phase transitions. We found that there are obvious discrepancies between the positions of the hydrogen atoms obtained by the X-ray data and the ones obtained by the neutron data. This result indicates that the centers of the electron cloud of the hydrogen atoms are off from the nuclear positions. The discrepancy is markedly seen in the hydrogen atoms participating in the hydrogen-bonds. That is, there are local electronic dipolemoments in the hydrogen-bond region.