A new supramolecular semiconductor palladium(ii) complex [(CH3)3N(CH2)3Br]2Pd2Cl6: structural study, optical and electrical properties

Abstract

Hybrid organic–inorganic lead-free halide materials have attracted widespread attention due to their applications in the field of optoelectronics. Herein, we synthesized a new binuclear Pd(II) complex templated by 3-bromopropyltrimethylammonium, which undergoes a high-temperature phase transition at about 428 K. Differential scanning calorimetry confirmed this reversible transformation with a large heat hysteresis of 65 K, which depicts a typical first-order phase transition in the compound. The X-ray crystal structure reveals that this material is composed of anionic dimers and organic cations. The complex, [(CH₃)₃N(CH₂)₃Br]₂Pd₂Cl₆, crystallizes in the monoclinic system, space group P2₁/c. The inorganic layer, built up by two crystallographically independent [Pd₂Cl₆]²⁻ dimer units, is connected to the [(CH₃)₃N(CH₂)₃Br]⁺ organic cations through C–H···Cl hydrogen bonds, which lead to a 3D supramolecular architecture. Each Pd atom is coordinated to two bridging Cl atoms in a slightly distorted square planar geometry. Furthermore, experimental results confirm the semiconducting behavior of [(CH₃)₃N(CH₂)₃Br]₂Pd₂Cl₆ with an optical bandgap of ∼2.2 eV. The electric properties were investigated in detail with the study of impedance and AC conductivity. Based on the Elliot theory, the conduction mechanism was deduced with two models: the overlapping polaron model (OLPT) is the right model describing the conduction in phase I, and the correlated barrier hopping model (CBH) describes the conduction in phase II.