Correlated structural, vibrational and dielectric properties of the [(C4H9)4N]2CoBr4 compound: origin of low-frequency polarization

Abstract

Organic–inorganic hybrid materials based on divalent metal halides constitute versatile platforms for tuning their physicochemical properties, with potential applications in optoelectronics, energy storage, and dielectric devices. Here, we present the first synthesis and complete characterization of [(C₄H₉)₄N]₂CoBr₄, a novel halogenocobaltate(II) compound. Hirshfeld surface analysis and single-crystal X-ray diffraction reveal a monoclinic structure composed of layered tetrabutylammonium cations and tetrahedral [CoBr₄]²⁻ units stabilized by strong C–H⋯Br interactions. The integrity of the organic and inorganic components is verified by vibrational spectroscopy (FT-IR and Raman). DSC analysis revealed the existence of two phase transitions at 335 K and 345 K. Electrical and dielectric tests, performed between 313 K and 353 K, demonstrated a phase transition around T = 338 K, as well as non-Debye relaxation processes, thermally activated charge transport, and semiconducting properties. At low frequencies, the dielectric permittivity reaches exceptionally high values (ε′ ≈ 10⁵), highlighting the strong dielectric response of this material and its potential relevance for functional dielectric and energy-storage applications. This study expands the family of functional halogenocobaltates(II) and provides valuable insights into the structure–property relationships that govern hybrid materials.