Budzianowski Armand, Petřiček Vaclav, Katrusiak Andrzej
National Centre for Nuclear Research, Andrzeja Sołtana 7, Otwock, Świerk 05-400, Poland.
Institute of Physics; Department of Structure Analysis, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, Prague 6 16253, Czech Republic.
IUCrJ. 2022 Jul 16;9(Pt 5):544-550. doi: 10.1107/S2052252522006406. eCollection 2022 Sep 1.
The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH]HOBr (where [dabcoH] = 1,4-di-aza-bicyclo-[2.2.2]octane dication) correspond to the general formula characteristic of perovskites. In enantiomorphic trigonal polymorph α of [dabcoH]HOBr , the corner-sharing [HO]Br octahedra combine into a 3D framework embedding [dabcoH] dications in pseudo-cubic cages. In the more dense polymorph β, the face-sharing [HO]Br octahedra form 1D polyanionic columns separated by [dabcoH] dications. These different topologies correlate with different crystal fields around the cations and their different disorder types: orientational disorders of [dabcoH] dications and HO cations in polymorph α and positional disorder of [HO] cations in polymorph β. The orientational disorder increases the lengths of OH⋯Br hydrogen bonds in polymorph α, but NH⋯Br distances of ordered dabcoH dications are longer in polymorph β. The presence of polar [HO] cations in [dabcoH]HOBr polymorphs offers additional polarizability of the centres compared with analogous metal-free [dabcoH][NH]Br perovskite.
一种新型无金属且无铵的化合物[dabcoH]HOBr（其中[dabcoH] = 1,4 - 二氮杂双环-[2.2.2]辛烷二价阳离子）的结构和化学计量对应于钙钛矿的通式。在[dabcoH]HOBr的对映体三方多晶型α中，共角的[HO]Br八面体结合形成一个三维框架，将[dabcoH]二价阳离子嵌入伪立方笼中。在密度更大的多晶型β中，共面的[HO]Br八面体形成由[dabcoH]二价阳离子隔开的一维聚阴离子柱。这些不同的拓扑结构与阳离子周围不同的晶体场及其不同的无序类型相关：多晶型α中[dabcoH]二价阳离子和HO阳离子的取向无序以及多晶型β中[HO]阳离子的位置无序。取向无序增加了多晶型α中OH⋯Br氢键的长度，但有序的dabcoH二价阳离子的NH⋯Br距离在多晶型β中更长。与类似的无金属[dabcoH][NH]Br钙钛矿相比，[dabcoH]HOBr多晶型中极性[HO]阳离子的存在提供了额外的中心极化率。
