Mercury (II) compound with a quaternary phosphonium: X-ray structure, Hirshfeld surface analysis, optical band gap, and dielectric properties

A new bis(tetrabutylphosphonium) hexachlorodimercurate (II) [(C₄H₉)₄P]₂Hg₂Cl₆(1) was synthesized by slow evaporation method at room temperature and characterized by single-crystal X-ray diffraction (XRD), Hirshfeld surface analysis, UV–Vis spectroscopy, and complex impedance. The synthesized compound adopts the triclinic symmetry and crystallizes in the centrosymmetric space group P \(\overline{1}\) $\overline{1}$ with the following unit cell parameters: a = 11.877 (5) Å, b = 15.346 (6) Å, c = 15.417 (6) Å, α = 69.13 (2)°, β = 73.28 (2)°, and γ = 74.89 (2)°. The dimers [Hg₂Cl₆]²⁻ and the tetrabutylphosphonium cations [(C₄H₉)₄P]⁺ are related together by C–H⋯Cl hydrogen bonds and electrostatic interactions. The Hirshfeld surface analysis was used to discuss the strength of hydrogen bonds and to quantify the intermolecular contacts (two-dimensional (2D) fingerprint plots). The optical absorption measurement showed a semiconductor behavior with a band gap of approximately 3.26 eV. Moreover, the dielectric properties and ac conductivity have been investigated to explain the nature of the transport mechanism and relaxation process in our material.