Nuclear magnetic resonance (NMR) shielding constants have been calculated for Ni(II) bis(pentafluorophenyl)norcorrole and its face-to-face stacked dimer at the Hartree–Fock (HF), second-order Møller–Plesset perturbation theory (MP2), complete-active-space self-consistent-field (CASSCF) levels as well as at density functional theory (DFT) levels using several functionals. The calculated ¹H NMR shielding constants agree rather well with the experimental ones. The shielding constants of N and Ni calculated at DFT, HF, and MP2 levels differ from those obtained in the CASSCF calculations due to near-degeneracy effects at the Ni atom. The calculated magnetically induced current densities show that the monomer is antiaromatic, sustaining a strong global paratropic ring current, and the dimer is aromatic, sustaining a strong diatropic ring current. Qualitatively the same current density is obtained at the employed levels of theory. The most accurate ring-current strengths are probably obtained at the MP2 level. The aromatic dimer has a short intermolecular distance of less than 3 Å. The intermolecular interaction changes the nature of the frontier orbitals leading to a formal double bond between the norcorrole macrocycles.

中文翻译：

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通过堆积改变芳香特性：Ni(II) 双(五氟苯基)降咯咯的面对面二聚体

根据 Hartree-Fock (HF)、二阶 Møller-Plesset 微扰理论 (MP2) 计算了 Ni( II ) 双(五氟苯基)降咯咯及其面对面堆叠二聚体的核磁共振 (NMR) 屏蔽常数、完全活动空间自洽场 (CASSCF) 级别以及使用多种泛函的密度泛函理论 (DFT) 级别。计算的¹ H NMR 屏蔽常数与实验值吻合得很好。由于 Ni 原子的近简并效应，在 DFT、HF 和 MP2 水平下计算的 N 和 Ni 的屏蔽常数与 CASSCF 计算中获得的屏蔽常数不同。计算的磁感应电流密度表明，单体是反芳香族的，维持着强大的全局顺向环电流，而二聚体是芳香族的，维持着强的向异性环电流。在所采用的理论水平上定性地获得了相同的电流密度。最准确的环流强度可能是在 MP2 级别获得的。芳香族二聚体的分子间距离短，小于3 Å。分子间相互作用改变了前沿轨道的性质，导致去甲咯大环之间形成正式双键。