Crystal Growth, Structural Characterization of a Novel Semiconductor Promising Iron(III) Chloride-Based Coordination Complex: A Potential Low-Bandgap Material for Improved Solar Cell Performance

In this work, we demonstrate a novel mononuclear complex with remarkable electrical and dielectric properties formulated as [Fe-(HPDC)-(H₂O)-Cl₂] (<b>HM2</b>) (H₂PDC = 2,6-Pyridinedicarboxylic acid) prepared using the slow evaporation method conducted at ambient temperature. Single-crystal X-ray diffraction was applied to precisely explore the compound's structural characteristics. At room temperature, The <b>HM2</b> structure crystallizes in the monoclinic crystal system and belongs to the <i>P</i>2₁/<i>c</i> space group, as defined by the following lattice parameters: <i>a</i> = 6.3930(7) Å, <i>b</i> = 17.284(2) Å, <i>c</i> = 9.8074(9) Å, β = 105.945(11)°, <i>V</i> = 1042.0(2) ų and <i>D</i> _<i>x</i> = 1.975 g.cm^-3. The stability of the structure is preserved through noncovalent interactions such as O-H···O and O-H···Cl bonds. Hirshfeld surface analysis along with 2D fingerprint plots provide extended visualization, highlighting the most significant interactions as O···H/H···O and Cl···H/H···Cl contacts. Furthermore, the spectroscopic examination was performed using both infrared (IR) and Raman methods to explore the vibrational characteristics associated with organic and inorganic parts, confirming the hybrid nature of the title compound. The compound exhibits broad absorption across the visible spectrum with an optical band gap of 1.8 eV, indicating its semiconducting properties and efficient absorption of sunlight at various wavelengths. The electronic band structure and density of states (DOS) for the <b>HM2</b> compound were computed, revealing a band gap energy of 1.8 eV. These properties are critical in solar energy conversion devices and photovoltaic technology. Systematic characterizations, including differential scanning calorimetry (DSC) and electrical measurements, found that no phase transitions occurred between 300 and 453 K, which is sensitive for potential thermally resilient fields. A thorough analysis of the electric and dielectric properties revealed a low dielectric loss at high frequencies and a significant dielectric constant at lower frequencies. These findings underline their excellent dielectric potential, especially for electronic devices and battery applications.