Heck Joshua, Kucenko Anastasia, Hoffmann Alexander, Herres-Pawlis Sonja
Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany.
Dalton Trans. 2024 Jul 30;53(30):12527-12542. doi: 10.1039/d4dt01539h.
In a previous study, we showed that the properties and the ability as an entatic state model of copper guanidine quinoline complexes are significantly influenced by a methyl or methyl ester substituent in the 2-position. To prove the importance of the 2-position of the substituent, two novel guanidine quinoline ligands with a methyl or methyl ester substituent in the 4-position and the corresponding copper complexes were synthesized and characterized in this study. The influence of the substituent position on the copper complexes was investigated with various experimental and theoretical methods. The molecular structures of the copper complexes were examined in the solid state by single-crystal X-ray diffraction (SCXRD) and by density functional theory (DFT) calculations indicating a strong dependency on the substituent position compared to the systems substituted in the 2-position from the previous study. Further, the significantly different influence on the donor properties in dependency on the substituent position was analyzed with natural bond orbital (NBO) calculations. By the determination of the redox potentials, the impact on the electrochemical stabilization was examined. With regard to further previously analyzed guanidine quinoline copper complexes, the electrochemical stabilization was correlated with the charge-transfer energies calculated by NBO analysis and ground state energies, revealing the substituent influence and enabling a comparatively easy and accurate possibility for the theoretical calculation of the relative redox potential. Finally, the electron transfer properties were quantified by determining the electron self-exchange rates the Marcus theory and by theoretical calculation of the reorganization energies Nelsen's four-point method. The results gave important insights into the dependency between the ability of the copper complexes as entatic state model and the type and position of the substituent.
在之前的一项研究中，我们表明，2-位上的甲基或甲酯取代基会显著影响胍基喹啉铜配合物作为张力态模型的性质和能力。为了证明取代基2-位的重要性，本研究合成并表征了两种在4-位带有甲基或甲酯取代基的新型胍基喹啉配体及其相应的铜配合物。采用各种实验和理论方法研究了取代基位置对铜配合物的影响。通过单晶X射线衍射（SCXRD）和密度泛函理论（DFT）计算对铜配合物的分子结构进行了固态研究，结果表明与之前研究中2-位取代的体系相比，其对取代基位置有很强的依赖性。此外，利用自然键轨道（NBO）计算分析了取代基位置对给体性质的显著不同影响。通过测定氧化还原电位，研究了其对电化学稳定性的影响。关于之前进一步分析的胍基喹啉铜配合物，电化学稳定性与通过NBO分析计算的电荷转移能和基态能相关，揭示了取代基的影响，并为相对氧化还原电位的理论计算提供了一种相对简单且准确的可能性。最后，通过Marcus理论测定电子自交换速率并利用Nelsen四点法对重组能进行理论计算，对电子转移性质进行了量化。结果为深入了解铜配合物作为张力态模型的能力与取代基类型和位置之间的依赖性提供了重要见解。
