Liu Tianyu, Holzapfel Noah P, Woodward Patrick M
Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210, USA.
IUCrJ. 2023 Jul 1;10(Pt 4):385-396. doi: 10.1107/S2052252523003743.
A symmetry mode analysis yields 47 symmetrically distinct patterns of octahedral tilting in hybrid organic-inorganic layered perovskites that adopt the n = 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 the a/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 the a and/or b axes 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 the a and/or b axes and θ-tilts (rotations) about the c axis. 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 Pb or Sn, favorable hydrogen bonding interactions can also be achieved by distortions of the octahedra in combination with θ-tilts.
对称模式分析得出了47种对称不同的八面体倾斜模式，这些模式存在于采用n = 1的Ruddlesden-Popper（RP）结构的有机-无机杂化层状钙钛矿中。将属于该家族的化合物的晶体结构与对称分析的预测结果进行了比较。在140种独特结构中，约88%的结构对称性与仅基于八面体倾斜所预期的对称性一致，而其余化合物具有进一步降低对称性的额外结构特征，例如庞大有机阳离子的不对称堆积、金属中心八面体的畸变或无机层的偏移，该偏移偏离了与RP结构相关的a/2 + b/2偏移。实际化合物的结构在各种倾斜系统中呈非均匀分布，47种倾斜系统中仅出现了9种。未发现关于未畸变母体结构的a和/或b轴的同相ψ倾斜的例子，而在另一个极端情况下，约66%的已知结构具有关于a和/或b轴的异相φ倾斜以及关于c轴的θ倾斜（旋转）的组合。后一种组合导致了有利的氢键相互作用，从而在无机层中容纳化学性质不等价的卤离子。在一些化合物中，主要是那些含有Pb或Sn的化合物，八面体畸变与θ倾斜相结合也可以实现有利的氢键相互作用。
