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Paramagnetic NMR of phenolic oxime copper complexes: a joint experimental and density functional study

机译:酚肟铜配合物的顺磁NMR:联合实验和密度泛函研究

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摘要

H and C pNMR properties of bis(salicylaldoximato)copper(II) were studied in the solid state using magic-angle-spinning NMR spectroscopy and, for the isolated complex and selected oligomers, using density-functional theory at the PBE0 // PBE0-D3 level. Large paramagnetic shifts are observed, up to δ(H) = 272 ppm and δ(C) = 1006 ppm (at 298 K), which are rationalised through spin delocalisation from the metal onto the organic ligand and the resulting contact shifts arising from hyperfine coupling. The observed shift ranges are best reproduced computationally using exchange-correlation functionals with a high fraction of exact exchange (such as PBE0). Through a combination of experimental techniques and first-principles computation, a near-complete assignment of the observed signals is possible. Intermolecular effects on the pNMR shifts, modelled computationally in the dimers and trimers through effective decoupling between the local spins via A-tensor and total spin rescaling in the pNMR expression, are indicated to be small. Addition of electron-donating substituents and benzannelation of the organic ligand is predicted computationally to induce notable changes in the NMR signal pattern, suggesting that pNMR spectroscopy can be a sensitive probe for the spin distribution in paramagnetic phenolic oxime copper complexes.
机译:使用幻角旋转NMR光谱研究了固态的双(水杨基醛固酮)铜(II)的H和C pNMR性质,对于分离的复合物和选定的低聚物,使用密度泛函理论在PBE0 // PBE0- D3级。观察到较大的顺磁位移,最高δ(H)= 272 ppm和δ(C)= 1006 ppm(在298 K下),这是通过从金属到有机配体的自旋离域化以及由超精细产生的接触位移而合理化的耦合。观察到的移位范围最好使用具有较高精确交换比例(例如PBE0)的交换相关函数进行计算重现。通过结合实验技术和第一性原理计算,可以对观察到的信号进行几乎完全的分配。分子间对pNMR位移的影响很小,这是通过在局部自旋之间通过A-tensor进行有效解耦和在pNMR表达中的总自旋重缩放而在二聚体和三聚体中进行计算建模的。通过计算可预测,给电子取代基的添加和有机配体的苯甲酰化会引起NMR信号模式的显着变化,这表明pNMR光谱学可能是顺磁性酚醛肟铜络合物中自旋分布的灵敏探针。

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