Structural characterization, thermal analysis, electric and dielectric properties of a novel organic-inorganic hybrid compound based on iron fluoride

•A novel hybrid compound, formulated as (H2Piper)4[(FeF6)2FeF5(H2O)(H2O)4], has been synthesized by hydrothermal method.•The thermal studies of the title compound show the presence of two-phase transitions.•The phase transitions are confirmed by the electrical and dielectric study.•The ac conductivity frequency dependence is analyzed by Jonscher's universal power law. [Display omitted] A novel organic–inorganic hybrid compound based on iron fluoride, formulated as (H2Piper)4[(FeF6)2FeF5(H2O)(H2O)4] (Piper = Piperazine), C1, has been synthesized through hydrothermal method and characterized by X-ray single-crystal diffraction, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and dielectric measurements. Single-crystal X-ray study demonstrated that C1 crystallizes in P1̅ space group with lattice parameters: a = 12.5535(5) Å, b = 12.8715(4) Å, c = 22.2774(8) Å, α = 92.321(3)°, β = 95.957 (3)°, γ = 91.946(3)°, V = 3574.6 Å3 and Z = 4. In the molecular arrangement, [FeF6]3- and [FeF5(H2O)]2- anions are connected to [H2Piper]2+ cations and free water molecules through hydrogen bonds (O–H⋅⋅⋅F and N–H⋅⋅⋅F) generating 3D network. Thermal analysis (DSC and TG) of C1 confirmed the presence of two phase transitions as well as the temperature of the decomposition of the hybrid material. The complex impedance of C1 was investigated in the temperature range 410–530 K and in the frequency range 200–2.106 Hz. Additionally, an electrical equivalent circuit was reported to explain the impedance results. The variation of the dc and ac conductivity corroborated two phase transitions of the title compound. Furthermore, the frequency dependence of alternative current (ac) conductivity was interpreted in terms of Jonscher's law. The alternative current (ac) electrical conduction in C1 material was accounted for in terms of two processes that can be assigned to the hopping transport mechanism (CBH and NSPT model). The temperature dependences of dielectric permittivity indicated a relaxation process and highlighted the good protonic conduction of this material.