X-ray and neutron structure analysis of MeHPLN in the low temperature phase

Structure analyses of 5-Methyl-9-hydroxyphenalenon(C14H10O2, MeHPLN) in the low temperature phase were performed by X-ray and neutron scattering experiments. It is found that the space croup is P2(1)/c with a super cell (a x 2b x c) and there are two types of molecules in the unit cell. In one of the independent molecules, hydrogen atoms in hydrogen-bond region occupy two sites as same as in the room temperature phase. On the other hand, in another independent molecules, hydrogen atoms in hydrogen-bond region clearly show ordering feature. In these ordered hydrogen atoms, there are obvious discrepancy beween electron and nuclear distribution, and hence static electrical dipolemoments exist in hydorgen-bond region with an antiferroelectric ordering.