Exploration of new chiral hybrid semiconducting palladium halide complexes: [(R)/(S)-2-Methylpiperazinediium]PdCl4

Abstract

Chiral organic-inorganic halogenometallate hybrids have attracted significant research interest in various fields from optoelectronic to photovoltaic devices. However, to this day the range of available chiral hybrid metal halides still remains limited. In this context, single crystals of organically templated chiral chloropalladate (II), [(R)/(S)-C5H14N2]PdCl4, have been synthesized. Each of the chiral molecular compound consists of (R) or (S)-2-methylpiperazinediium [C5H14N2]2+ cations and [PdCl4]2− anions. The complexes, [(R)/(S)-C5H14N2]PdCl4 crystallize in the chiral space group P212121 (No. 19), which exhibits the enantiomorphic crystal class 222 (D2). In the crystal structure, the [PdCl4]2− anions are linked to the organic cations through NH…Cl and CH…Cl hydrogen bonds to form cation-anion-cation molecular units. The incorporation of a protonated (R) or (S)-2-methylpiperazine cations into the same inorganic halide systems leads to similar properties. The thermal analysis, optical and electric properties of [(R)-C5H14N2]PdCl4 (1) compound have been studied. The title compound [(R)-C5H14N2]PdCl4 (1) reveals thermal stability up to ca. 450 K. Besides, [(R)-C5H14N2]PdCl4 (1) shows semiconducting behavior with an optical band gap of ∼3.64 eV. The electric properties are investigated and the equivalent circuit is chosen and confirms the contribution of the grain and grain boundaries. The values of AC conductivities (10−6 Ω−1cm−1) confirm the gap energy and the semiconducting character of the R enantiomer. The value of activation energy is determinated and shows the ionic conduction type. Such a chiral hybrid metal halide offers a viable strategy for the targeted design and synthesis of non-centrosymmetric metal halide materials for optoelectronic applications.