Following an isosymmetric phase transition by changes in bond lengths and anisotropic displacement parameters: the case of meta-carboxyphenylammonium phosphite.

Crystal structure studies in the 100-345 K temperature range were performed to relate the molecular structure changes of meta-carboxyphenylammonium phosphite (m-CPAMP) to its first-order phase transition at T(c) = 246 (2) K. Thermal displacement parameters and most bond distances show an abrupt jump at the transition. Such a structural change is related to collective effects leading to competition between intra- and intermolecular interactions.