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Hybrid n = 1 Ruddlesden-Popper perovskites with aromatic ammonium cations like benzylammonium (BzA) and phenethylammonium (PEA) have been shown to adopt polar structures and exhibit ferroelectricity, but many of the examples discovered thus far contain either Pb or Cd. Here, we describe the synthesis and structural characteriza-tion of four layered halide double perovskites: (BzA)4AgBiBr8, (PEA)4AgBiBr8, (BzA)4AgInCl8, and (PEA)4AgInCl8. In all four compounds the inorganic layers exhibit a chessboard ordering of Ag+ and Bi3+/In3+ and the layers stack in a coherent pattern that maintains the ordering over three-dimensional space. The octahedra sur-rounding Ag+ show a large axial compression, which results in much shorter bonds to the terminal halide ions than to the bridging halide ions, whereas the bismuth- and indium-centered octahedra show only small distortions. There appears to be a competition between polar distortions of the octahedra and octahedral tilting, both of which can optimize hydrogen bonding interactions between the ammonium cations and the inorganic layers. Unlike the Pb- or Cd-containing analogs, the double perovskites seem to favor patterns of octahedral tilting that suppress po-lar ordering of the organic cations. The packing of the organic cations depends on both their conformational flexi-bility and the lateral dimensions of the inorganic layer. These forces favor intra-layer edge-to-face interaction be-tween aromatic rings in the three of the four compounds. The lone exception is (PEA)4AgBiBr8, which forms weak inter-layer edge-to-face interactions between aromatic rings and slip-stacked packing within each organic layer.
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Understanding structural distortions in hybrid layered perovskites with the n = 1 Ruddlesden–Popper structure
A symmetry mode analysis yields 47 symmetrically distinct patterns of octahedral tilting in hybrid organic–inorganic layered perovskites that adopt then= 1 Ruddlesden–Popper (RP) structure. The crystal structures of compounds belonging to this family are compared with the predictions of the symmetry analysis. Approximately 88% of the 140 unique structures have symmetries that agree with those expected based on octahedral tilting alone, while the remaining compounds have additional structural features that further lower the symmetry, such as asymmetric packing of bulky organic cations, distortions of metal-centered octahedra or a shift of the inorganic layers that deviates from thea/2 +b/2 shift associated with the RP structure. The structures of real compounds are heterogeneously distributed amongst the various tilt systems, with only 9 of the 47 tilt systems represented. No examples of in-phase ψ-tilts about theaand/orbaxes of the undistorted parent structure were found, while at the other extreme ∼66% of the known structures possess a combination of out-of-phase ϕ-tilts about theaand/orbaxes and θ-tilts (rotations) about thecaxis. The latter combination leads to favorable hydrogen bonding interactions that accommodate the chemically inequivalent halide ions within the inorganic layers. In some compounds, primarily those that contain either Pb2+or Sn2+, favorable hydrogen bonding interactions can also be achieved by distortions of the octahedra in combination with θ-tilts.
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- Award ID(s):
- 2003793
- PAR ID:
- 10507667
- Publisher / Repository:
- International Unioni of Crystallography
- Date Published:
- Journal Name:
- IUCrJ
- Volume:
- 10
- Issue:
- 4
- ISSN:
- 2052-2525
- Page Range / eLocation ID:
- 385 to 396
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1107/S2052252523003743
