Beschreibung:
<jats:p>The present article is devoted to the characterization of the structural phase transitions of the [CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>][Co(COOH)<jats:sub>3</jats:sub>] (<jats:bold>1</jats:bold>) perovskite-like metal–organic compound through variable-temperature single-crystal neutron diffraction. At room temperature, compound<jats:bold>1</jats:bold>crystallizes in the orthorhombic space group<jats:italic>Pnma</jats:italic>(phase<jats:bold>I</jats:bold>). A decrease in temperature gives rise to a first phase transition from the space group<jats:italic>Pnma</jats:italic>to an incommensurate phase (phase<jats:bold>II</jats:bold>) at approximately 128 K. At about 96 K, this incommensurate phase evolves into a second phase with a sharp change in the modulation vector (phase<jats:bold>III</jats:bold>). At lower temperatures (<jats:italic>ca</jats:italic>78 K), the crystal structure again becomes commensurate and can be described in the monoclinic space group<jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>n</jats:italic>(phase<jats:bold>IV</jats:bold>). Although phases<jats:bold>I</jats:bold>and<jats:bold>IV</jats:bold>have been reported previously [Boča<jats:italic>et al.</jats:italic>(2004).<jats:italic>Acta Cryst.</jats:italic>C<jats:bold>60</jats:bold>, m631–m633; Gómez-Aguirre<jats:italic>et al.</jats:italic>(2016).<jats:italic>J. Am. Chem. Soc.</jats:italic><jats:bold>138</jats:bold>, 1122–1125; Mazzuca<jats:italic>et al.</jats:italic>(2018).<jats:italic>Chem. Eur. J.</jats:italic><jats:bold>24</jats:bold>, 388–399], phases<jats:bold>III</jats:bold>and<jats:bold>IV</jats:bold>corresponding to the<jats:italic>Pnma</jats:italic>(00γ)0<jats:italic>s</jats:italic>0 space group have not yet been described. These phase transitions involve not only the occurrence of small distortions in the three-dimensional anionic [Co(HCOO)<jats:sub>3</jats:sub>]<jats:sup>−</jats:sup>framework, but also the reorganization of the [CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>]<jats:sup>+</jats:sup>counter-ions in the cavities of the structure, which gives rise to an alteration of the hydrogen-bonded network, modifying the electrical properties of compound<jats:bold>1</jats:bold>.</jats:p>