Zarychta Bartosz, Zaleski Jacek, Kyzioł Janusz, Daszkiewicz Zdzisław, Jelsch Christian
Faculty of Chemistry, University of Opole, Poland.
Acta Crystallogr B. 2011 Jun;67(Pt 3):250-62. doi: 10.1107/S0108768111013140. Epub 2011 May 14.
Nitramines and related N-nitro compounds have attracted significant attention owing to their use in rocket fuel and as explosives. The charge density of 1-nitroindoline was determined experimentally and from theoretical calculations. Electron-density refinements were performed using the multipolar atom formalism. In order to design the ideal restraint strategy for the charge-density parameters, R-free analyses were performed involving a series of comprehensive refinements. Different weights were applied to the charge-density restraints, namely the similarity between chemically equivalent atoms and local symmetry. Additionally, isotropic thermal motion and an anisotropic model calculated by rigid-body analysis were tested on H atoms. The restraint weights which resulted in the lowest values of the averaged R-free factors and the anisotropic H-atom model were considered to yield the best charge density and were used in the final refinement. The derived experimental charge density along with intra- and intermolecular interactions was analysed and compared with theoretical calculations, notably with respect to the symmetry of multipole parameters. A comparison of different refinements suggests that the appropriate weighting scheme applied to charge-density restraints can reduce the observed artefacts. The topological bond orders of the molecule were calculated.
硝胺及相关的N-硝基化合物因其在火箭燃料和炸药中的应用而备受关注。通过实验和理论计算确定了1-硝基吲哚啉的电荷密度。使用多极原子形式进行电子密度精修。为了设计电荷密度参数的理想约束策略，进行了涉及一系列全面精修的R-自由分析。对电荷密度约束应用了不同的权重，即化学等价原子之间的相似性和局部对称性。此外，对H原子测试了通过刚体分析计算的各向同性热运动和各向异性模型。导致平均R-自由因子值最低的约束权重和各向异性H原子模型被认为能产生最佳电荷密度，并用于最终精修。分析了导出的实验电荷密度以及分子内和分子间相互作用，并与理论计算进行了比较，特别是关于多极参数的对称性。不同精修的比较表明，应用于电荷密度约束的适当加权方案可以减少观察到的伪影。计算了分子的拓扑键级。
