Structural and physico-chemical characterization of hybrid materials based on globular quinuclidinium cation derivatives and tetrachloridocobaltate(ii) anions

Abstract

The present study explores the effect of local symmetry breaking of globular cations on the formation and properties of hybrid organic–inorganic materials based on tetrahalometallate anions. To this end, a crystal engineering approach was employed to design and synthesize three novel compounds, namely (quinuclidinium)₂[CoCl₄] (A), ((R,S)-3-aminoquinuclidinium)[CoCl₄] (B) and ((R)-(−)-3-hydroxyquinuclidinium)₂[CoCl₄] (C). The thermal, structural, magnetic and electrical properties of these compounds were investigated using a comprehensive array of characterization techniques, including differential scanning calorimetry, single crystal X-ray diffraction, variable temperature synchrotron X-ray powder diffraction, and powder and single crystal neutron diffraction. Our results demonstrate that compounds A and C exhibit a structural phase transition above 322 and 340 K, respectively, resulting in a mesophase-like state featured by a sharp dielectric anomaly, which is attributed to the molecular dynamics of the organic cations in their rotational state. Moreover, compound C also displays an additional crystal phase transition at around 200 K as a result of the formation of a superstructure along the c-axis direction. On the other hand, compound B shows a possible diffusion phenomenon around 350 K related to dielectric permittivity changes. In terms of magnetic behaviour, all the compounds present antiferromagnetic interactions between tetrachloridocobaltate anions without long-range magnetic ordering down to 2 K. Overall, this study provides valuable insights at the molecular level into the impact of local symmetry breaking of the quinuclidinium cation in combination with the synergistic effect of the tetrachloridocobaltate anion on the structural, magnetic and dielectric properties, thus contributing to the progress of cutting-edge functional hybrid organic–inorganic materials.