DOI: https://doi.org/10.55373/mjchem.v28i5.13

Keywords: Thiosemicarbazide, HOMO-LUMO, crystal structure, polymer electrolyte, conductivity

Abstract

Thiosemicarbazides are valued for their biological activities and versatile applications, with nitrogen and sulfur donor atoms offering new potential in polymer electrolyte studies. The main goal of this research is to synthesize and characterize 4-(3-bromophenyl) thiosemicarbazide and investigate its conductivity. 4-(3-bromophenyl)thiosemicarbazide was prepared by reacting 3-bromophenyl isothiocyanate with hydrazine hydrate and was successfully synthesized in 89% yield. CHNS analysis confirmed its high purity with <1% deviation from theoretical values. FTIR (cm⁻¹): 3275, 3146 [ν(N-H)]; 1632 [δ(NH₂) + ν(C=C)ₐᵣ]; 1571 [ν(C=C)ₐᵣ]; 1524 [δ(N-H)]; 1211 [ν(C=S)]; 1076 [ν(C-N)]; 763 [γ(C-H)ₐᵣ]; 696 [ν(C-Br)]. ¹³C NMR displayed signals at 180 ppm (C=S) and 121–141 ppm (aromatic carbons), confirming the proposed structure. UV-Vis spectra showed absorption at 270 and 212 nm, assigned to π→π* and n→σ* transitions, respectively. Thermogravimetric analysis revealed a multi-step decomposition, indicating its thermal stability. Single-crystal XRD revealed a monoclinic crystal system (space group P2₁/n) with unit cell parameters a = 6.2948(4) Å, α = 90°; b = 28.1751(18) Å, β = 99.168(2)°; c = 10.8098(7) Å, γ = 90°, revealing intermolecular N–H··S and N–H··Br hydrogen bonds, and C–H··π and N–H··π interactions. The UV-Vis Tauc plot gave a band gap of 5.36 eV, while DFT calculated 4.92 eV, indicating a wide-band-gap electronic structure. EIS measurements indicated an ionic conductivity of 8.87 × 10⁻⁵ S cm⁻¹ at room temperature for the sample containing 10 wt% additive. Upon incorporation of 5 wt% 2,6-pyridinedicarboxylic acid, the conductivity increased by 8.3-fold to 7.32 × 10⁻⁴ S cm⁻¹ at room temperature, reaching a maximum of 8.60 × 10⁻⁴ S cm⁻¹ at 50 °C, beyond which thermal degradation effects reduce conductivity. Temperature-dependent studies revealed non-Arrhenius behavior, with conductivity peaking at 50°C (8.60 × 10⁻⁴ S cm⁻¹) and declining at higher temperatures, consistent with a negative apparent activation energy (E_a = −2.21 kJ/mol) arising from thermal degradation effects that dominate above 50°C. Thus, the material shows great potential as a conductive additive for polymer electrolyte-based energy storage applications, with tunable ionic transport properties within its operational temperature window (<50°C).