Two-Electron Multicenter Bonding (‘Pancake Bonding’) in Dimers of 5,6-Dichloro-2,3-dicyanosemiquinone (DDQ) Radical Anions,Crystal Growth & Design

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Two-Electron Multicenter Bonding (‘Pancake Bonding’) in Dimers of 5,6-Dichloro-2,3-dicyanosemiquinone (DDQ) Radical Anions
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2020-07-09 , DOI: 10.1021/acs.cgd.0c00658
Valentina Milašinović ₁ , Anna Krawczuk ₂ , Krešimir Molčanov ₁ , Biserka Kojić-Prodić ₁

Affiliation

An X-ray charge density study of 4-cyano-N-methylpyridinium salt of 5,6-dichloro-2,3-dicyanosemiquinone radical anion ([4-CN-N-MePy]⁺[DDQ]⁻) revealed fine details of two-electron multicenter (2e/mc) covalent bonding within stacked dimers of DDQ anion radicals with a short separation distance of 2.87 Å. Since the electron pair is not localized but rather spread over a large area between two semiquinoid rings (28 atoms), the maximum electron density is 0.085 e Å^–3; the electron density value is consistent with the existence of a nonlocalized electron pair. However, the presence of multiple bond (3,–1) critical points and a local electron density minimum (which is usually found in cage-like moieties, such as adamantyl) between the rings point to a 3D shape of frontier orbitals, consistent with the presence of a 2e/mc bond.

中文翻译：

5,6-Dichloro-2,3-dicyanosemiquinone（DDQ）自由基阴离子的二聚体中的双电子多中心键合（“薄饼键合”）

X-射线研究了5,6-二氯-2,3-二氰基米醌自由基阴离子（[4-CN- N -MePy] ⁺ [DDQ] ^-）的4-氰基-N-甲基吡啶鎓盐的细节。 DDQ阴离子自由基的堆叠二聚体中的双电子多中心（2e / mc）共价键合，分隔距离短，为2.87Å。由于电子对未进行本地化，而是扩展到两个semiquinoid环（28个原子）之间的大的面积，最大电子密度是0.085 E中的^-3; 电子密度值与非局部电子对的存在一致。然而，在环之间存在多个键（3，–1）临界点和局部电子密度最小值（通常在笼状部分，如金刚烷基中发现）指向边界轨道的3D形状，与2e / mc键的存在。

更新日期：2020-08-05

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