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晶体结构预测和三种小分子含卤有机化合物的同晶型性。

Crystal structure prediction and isostructurality of three small organic halogen compounds.

机构信息

Institute of Pharmaceutical Innovation, University of Bradford, Bradford, BD7 1DP, UK.

出版信息

Phys Chem Chem Phys. 2010 Aug 14;12(30):8571-9. doi: 10.1039/c003971c. Epub 2010 Jun 8.

Abstract

A theoretical investigation of the packing stabilities of three small organic halogen compounds is presented based on a crystal structure prediction (CSP) study. Each compound has four identical halogen atoms (fluorine, chlorine, and bromine) and a four-membered ring consisting of carbon and sulfur atoms arranged alternately. Two halogen atoms are attached to each carbon and two oxygen atoms are attached to each sulfur forming SO(2) functional groups. The crystal structures of these compounds have been determined experimentally and show distinct packing arrangements. Utilising the computational approaches implemented in the GRACE software package, each compound is subjected to a full CSP study using a force field specific for each molecule (called the tailor-made force field or TMFF) and a dispersion corrected solid-state density functional method (or DFT(d) method). Energetically feasible crystal structures are generated in all 230 space groups restricted to a single molecule in the crystallographic asymmetric unit (Z' = 1) using the TMFF of each molecule. Next, a selection of structures with low TMFF lattice energies are further refined with the DFT(d) method. The CSP results show that the experimental crystal structures of the molecules containing fluorine and chlorine are well described energetically and geometrically by their TMFFs and the DFT(d) method. Both approaches locate their experimental lattices as the most stable structures. For the molecule containing bromine, a crystal structure corresponding to the force field optimised experimental structure is located as the second structure in the list of force field predicted structures, ranked by calculated lattice energy. Despite the structural similarity of the predicted and experimental structures, close examination of the DFT(d) optimisation results of the experimental structure reveals a slightly lower energy structure than that found by the CSP simulations. Furthermore, minimisation of the force field optimised structure using the DFT(d) method does not lead to the same minimum as the DFT(d) optimised experimental structure. Based on the CSP results and isostructurality among these three compounds, two new potential polymorphs for the molecules containing chlorine and bromine are proposed. These polymorphs might be obtained experimentally under the right crystallisation conditions.

摘要

基于晶体结构预测(CSP)研究,本文对三种小分子有机卤化物的堆积稳定性进行了理论研究。每个化合物都有四个相同的卤素原子(氟、氯和溴)和一个由碳和硫原子交替排列组成的四元环。每个碳原子上连接两个卤素原子,每个硫原子上连接两个氧原子,形成 SO(2)官能团。这些化合物的晶体结构已经通过实验确定,表现出明显的堆积排列。利用 GRACE 软件包中实现的计算方法,每个化合物都使用特定于每个分子的力场(称为定制力场或 TMFF)和修正后的固态密度泛函方法(或 DFT(d)方法)进行全面的 CSP 研究。在限制晶体学不对称单元(Z'=1)中单个分子的情况下,使用每个分子的 TMFF 在所有 230 个空间群中生成能量可行的晶体结构。接下来,选择具有低 TMFF 晶格能的结构,并用 DFT(d)方法进一步优化。CSP 结果表明,含有氟和氯的分子的实验晶体结构在能量和几何上都很好地被其 TMFF 和 DFT(d)方法描述。两种方法都将实验晶格定位为最稳定的结构。对于含有溴的分子,与力场优化的实验结构对应的晶体结构被定位为力场预测结构列表中按计算晶格能排列的第二个结构。尽管预测结构和实验结构在结构上相似,但仔细检查实验结构的 DFT(d)优化结果表明,其能量比 CSP 模拟发现的要低一些。此外,使用 DFT(d)方法对力场优化结构进行最小化并不会导致与 DFT(d)优化实验结构相同的最小值。基于 CSP 结果和这三种化合物之间的同构性,提出了含有氯和溴的分子的两种新的潜在多晶型物。在适当的结晶条件下,这些多晶型物可能会通过实验获得。

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