Structure study of BrHPLN by X-ray and neutron diffraction

An antiferroelectric material with an isolated hydrogen bond, 5-bromo-9-hydroxyphenalenon, was structurally investigated by means of X-ray and neutron-diffraction methods at room temperature. It was found that the electron of the hydrogen atom in the hydrogen-bond region is in a disordered state, having three sites around the center of the hydrogen bond. We also found an obvious discrepancy between the electron density distribution and the nuclear density distribution. That is, the center of the electron cloud of the hydrogen atom is off set from the nuclear position. This result, together with the disordered feature, leads to a local disordered electronic dipole moment in the hydrogen-bond region, which is consistent with the result for 5-methyl-9-hydroxyphenalenon in its room-temperature phase.