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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical analysis of the influence of chelate-ring size and vicinal effects on electronic circular dichroism spectra of cobalt(III) EDDA-type complexes
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Theoretical analysis of the influence of chelate-ring size and vicinal effects on electronic circular dichroism spectra of cobalt(III) EDDA-type complexes

机译：螯合环大小和邻位效应对钴（III）EDDA型配合物的电子圆二色性光谱影响的理论分析

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摘要

To assess the contributions of configurational and vicinal effects as well as chelate-ring size to rotational strengths, the geometries of a series of cobalt(III) complexes [Co(EDDA-type)(L)]~± with the tetradentate EDDA-type ligands, EDDA (ethylenediamine-N,N′-diacetate), DMEDDA (N,N′-dimethylethylenediamine-N,N′-diacetate), DEEDDA (N,N′-diethylethylenediamine-N,N′-diacetate), and a bidentate ancillary ligand L (L = ethylenediamine, oxalate, carbonate, (S)-alanine, and malonate) in aqueous solution have been optimized at the DFT/B3LYP/6-311++G(2d, p) level of theory. Based on the optimized geometries, the excitation energies and oscillator and rotational strengths have been calculated using the time-dependent density functional theory (TDDFT) method with the same functional and basis set. The calculated circular dichroism (CD) curves are in excellent agreement with the observed ones except for some small red or blue shifts in peak wavelengths. For the influence of chelate-ring size of the bidentate ligands on the CD intensities, a qualitative analysis together with the quantitative TDDFT calculation reveal that it depends on the symmetry of the cobalt-EDDA backbone. For the s-cis-isomers, the influence is negligible due to the perturbation is symmetric. For the uns-cis-isomers, the perturbation is unsymmetric. Since a small ring size means a large perturbation, this leads to the integral CD intensities decreasing with increasing the chelate ring size. The vicinal effects of asymmetric nitrogens incorporate both the substitutent effects and conformational relaxation effects, with the former being dominant. By analyzing the contributions of chiral arrays to rotational strengths, we found that the part of contributions dominated by the S-type chiral nitrogens could be considered as a good measure for the vicinal effects of chiral nitrogens. In addition, we found that the twist form (δ/λ) of the backbone ethylenediamine ring (E-ring) of the coordinated EDDA-type ligands is a key factor to understand the properties of these chelates, because it not only dominates the relative stabilities of the s-cis-Λ(SS)-diastereoisomers with the result that λ > δ but also affects the major CD band by changing the order of the first two transitions. Moreover, the twist angle of E-ring is inversely related to the vicinal effect of chiral nitrogens. These findings may help us to understand the chelate ring size as well as vicinal effect related chiroptical phenomenon of the cobalt EDDA-type chelates.
机译：为了评估构型和邻域效应以及螯合环大小对旋转强度的贡献，一系列四齿EDDA型钴（III）配合物[Co（EDDA-型）（L）]〜±的几何形状配体，EDDA（乙二胺-N，N'-二乙酸酯），DMEDDA（N，N'-二甲基乙二胺-N，N'-二乙酸酯），DEEDDA（N，N'-二乙基乙二胺-N，N'-二乙酸酯）和水溶液中的双齿辅助配体L（L =乙二胺，草酸盐，碳酸盐，（S）-丙氨酸和丙二酸盐）已在DFT / B3LYP / 6-311 ++ G（2d，p）的理论水平上进行了优化。基于优化的几何形状，使用具有相同功能和基础集的时变密度泛函理论（TDDFT）方法，计算出了激发能，振荡器和旋转强度。计算出的圆二色性（CD）曲线与观察到的圆二色性曲线非常吻合，除了峰值波长有些小的红色或蓝色偏移。对于双齿配体的螯合环大小对CD强度的影响，定性分析和定量TDDFT计算表明，它取决于钴-EDDA主链的对称性。对于s-顺式异构体，由于微扰是对称的，因此影响可忽略不计。对于非顺式异构体，扰动是不对称的。由于小的环尺寸意味着较大的扰动，这导致积分的CD强度随螯合环尺寸的增加而减小。不对称氮的邻位效应兼有替代效应和构象松弛效应，前者占主导地位。通过分析手性阵列对旋转强度的贡献，我们发现以S型手性氮为主的部分贡献可被视为手性氮的邻位效应的一个很好的量度。此外，我们发现配位EDDA型配体的骨架乙二胺环（E环）的扭曲形式（δ/λ）是了解这些螯合物性质的关键因素，因为它不仅支配了相对螯合物顺式-Λ（SS）-非对映异构体的稳定性，结果λ>δ，但也通过改变前两个跃迁的顺序影响主要CD谱带。此外，E形环的扭转角与手性氮的邻位效应成反比。这些发现可能有助于我们了解钴EDDA型螯合物的螯合环大小以及与邻位效应相关的手足病现象。

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