Role of the Organic Cation in 2D Chiral Hybrid Palladium Chloride Materials

We report a series of new chiral and achiral organic-inorganic hybrid palladium chlorides and explore the influence of subtle changes to the organic cation on the structural, electronic, and chiroptical properties. These materials are (C₄H₁₀N)₂PdCl₄ ((C₄H₁₀N)⁺ = pyrrolidinium), R/S/racemic-(C₄H₉FN)₂PdCl₄ ((C₄H₉FN)⁺ = 3-fluoropyrrolidinium), and R/S/racemic-(C₅H₁₂N)₂PdCl₄ ((C₅H₁₂N)⁺ = 3-methylpyrrolidinium). R/S-(C₄H₉FN)₂PdCl₄ and R/S-(C₅H₁₂N)₂PdCl₄ are chiral metal halides, while (C₄H₁₀N)₂PdCl₄ and the racemic materials are achiral. Structurally, these materials are distorted Ruddlesden-Popper phase 2D perovskites. Pd²⁺ sits at the center of a distorted octahedron with four nearly identical 2.3 Å Pd-Cl bonds and two long (3.7-4.2 Å) Pd-Cl contacts. The long Pd-Cl contacts cause these materials to exhibit quasi-zero-dimensional electronic behavior with limited electronic coupling between Pd atoms. R- and S-(C₄H₉FN)₂PdCl₄ show appreciable circular dichroism signals, whereas R- and S-(C₅H₁₂N)₂PdCl₄ do not. We hypothesize that this difference originates from much stronger interactions between (C₄H₉FN)⁺ cations and the inorganic framework in R/S-(C₄H₉FN)₂PdCl₄ than in R/S-(C₅H₁₂N)₂PdCl₄, which is consistent with our observation that the R and S cations occupy distinct positions in racemic (C₄H₉FN)₂PdCl₄ but form a solid solution in racemic (C₅H₁₂N)₂PdCl₄. Our results highlight how small differences in the cation greatly affect the structural, electronic, and chiroptical properties of palladium(II) chloride materials.