Domasevitch Kostiantyn V, Senchyk Ganna A, Krautscheid Harald
Inorganic Chemistry Department, National Taras Shevchenko University of Kyiv, Volodymyrska Str. 64/13, 01601 Kyiv, Ukraine.
Institute of Inorganic Chemistry, Leipzig University, Johannisallee 29, D-04103 Leipzig, Germany.
Acta Crystallogr C Struct Chem. 2020 Jun 1;76(Pt 6):598-604. doi: 10.1107/S2053229620006762. Epub 2020 May 22.
Molecular crystals exhibiting polar symmetry are important paradigms for developing new electrooptical materials. Though accessing bulk polarity still presents a significant challenge, in some cases it may be rationalized as being associated with the specific molecular shapes and symmetries and subtle features of supramolecular interactions. In the crystal structure of 3,5,7-trinitro-1-azaadamantane, CHNO, the polar symmetry of the molecular arrangement is a result of complementary prerequisites, namely the C symmetry of the molecules is suited to the generation of polar stacks and the inherent asymmetry of the principal supramolecular bonding, as is provided by NO(lone pair)...NO(π-hole) interactions. These bonds arrange the molecules into a trigonal network. In spite of the apparent simplicity, the structure comprises three unique molecules (Z' = 1/3 + 1/3 + 1/3), two of which are donors and acceptors of three N...O interactions and the third being primarily important for weak C-H...O hydrogen bonding. These distinct structural roles agree with the results of Hirshfeld surface analysis. A set of weak C-H...O and C-H...N hydrogen bonds yields three kinds of stacks. The orientation of the stacks is identical and therefore the polarity of each molecule contributes additively to the net dipole moment of the crystal. This suggests a special potential of asymmetric NO(lone pair)...NO(π-hole) interactions for the supramolecular synthesis of acentric materials.
具有极性对称性的分子晶体是开发新型电光材料的重要范例。尽管实现体相极性仍然面临重大挑战，但在某些情况下，可以合理地认为这与特定的分子形状、对称性以及超分子相互作用的微妙特征有关。在3,5,7-三硝基-1-氮杂金刚烷（CHNO）的晶体结构中，分子排列的极性对称性是互补先决条件的结果，即分子的C对称性适合形成极性堆积，以及主要超分子键合的固有不对称性，如由NO（孤对）...NO（π-空穴）相互作用所提供的。这些键将分子排列成三角网络。尽管看似简单，但该结构包含三个独特的分子（Z' = 1/3 + 1/3 + 1/3），其中两个是三个N...O相互作用的供体和受体，第三个主要对弱C-H...O氢键起重要作用。这些不同的结构作用与 Hirshfeld 表面分析的结果一致。一组弱的C-H...O和C-H...N氢键产生三种堆积。堆积的取向相同，因此每个分子的极性对晶体的净偶极矩有累加贡献。这表明不对称的NO（孤对）...NO（π-空穴）相互作用在非中心材料的超分子合成中具有特殊潜力。
