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

High Resolution Image Download MS PowerPoint Slide 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 (C 4 H 10 N) 2 PdCl 4 ((C 4 H 10 N) + = pyrrolidinium), R/S/racemic-(C 4 H 9 FN) 2 PdCl 4 ((C 4 H 9 FN) + = 3-fluoropyrrolidinium), and R/S/racemic-(C 5 H 12 N) 2 PdCl 4 ((C 5 H 12 N) + = 3-methylpyrrolidinium). R/S-(C 4 H 9 FN) 2 PdCl 4 and R/S-(C 5 H 12 N) 2 PdCl 4 are chiral metal halides, while (C 4 H 10 N) 2 PdCl 4 and the racemic materials are achiral. Structurally, these materials are distorted Ruddlesden–Popper phase 2D perovskites. Pd 2+ 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-(C 4 H 9 FN) 2 PdCl 4 show appreciable circular dichroism signals, whereas R- and S-(C 5 H 12 N) 2 PdCl 4 do not. We hypothesize that this difference originates from much stronger interactions between (C 4 H 9 FN) + cations and the inorganic framework in R/S-(C 4 H 9 FN) 2 PdCl 4 than in R/S-(C 5 H 12 N) 2 PdCl 4, which is consistent with our observation that the R and S cations occupy distinct positions in racemic (C 4 H 9 FN) 2 PdCl 4 but form a solid solution in racemic (C 5 H 12 N) 2 PdCl 4 . Our results highlight how small differences in the cation greatly affect the structural, electronic, and chiroptical properties of palladium(II) chloride materials.