n-Propylammonium dihydrogenphosphate, C3H7NH3+.-H2PO4-, crystals are ferroe
lastic at room temperature. The phase transition into the prototypic phase
takes place at approximately 378 K. All atoms except two H atoms are linked
by the lost symmetry operations derived from the prototypic space group P2
/b2(1)/n2(1)/a. Each of these two different H atoms is involved in an asymm
etric hydrogen bond between an oxygen pair. Ferroelastic switching is conco
mitant with jumps of these H atoms from the donor to the acceptor O atoms.
The compound belongs to the structural family of n-alkylammonium dihydrogen
phosphate and in particular to the structure type of pentylammonium dihydro
genphosphate, which differs by localization of alternating layers from the
rest of the known alkylammonium dihydrogenphosphates. The crystal was sligh
tly twinned; the proportion of the minor domain was approximately 3.5%.