CEITEC-Central European Institute of Technology , Masaryk University , Kamenice 5/A4 , CZ-625 00 Brno , Czechia.
Hylleraas Centre for Quantum Molecular Science, Department of Chemistry , UiT-The Arctic University of Norway , N-9037 Tromsø , Norway.
Inorg Chem. 2018 Aug 6;57(15):8748-8759. doi: 10.1021/acs.inorgchem.8b00073. Epub 2018 Jul 13.
The links between the molecular structure and nuclear magnetic resonance (NMR) parameters of paramagnetic transition-metal complexes are still relatively unexplored. This applies particularly to the contact term of the hyperfine contribution to the NMR chemical shift. We report combining experimental NMR with relativistic density functional theory (DFT) to study a series of Ru(III) complexes with 2-substituted β-diketones. A series of complexes with systematically varied substituents was synthesized and analyzed using H and C NMR spectroscopy. The NMR spectra recorded at several temperatures were used to construct Curie plots and estimate the temperature-independent (orbital) and temperature-dependent (hyperfine) contributions to the NMR shift. Relativistic DFT calculations of electron paramagnetic resonance and NMR parameters were performed to interpret the experimental observations. The effects of individual factors such as basis set, density functional, exact-exchange admixture, and relativity are analyzed and discussed. Based on the calibration study in this work, the fully relativistic Dirac-Kohn-Sham (DKS) method, the GIAO approach (orbital shift), the PBE0 functional with the triple-ζ valence basis sets, and the polarizable continuum model for describing solvent effects were selected to calculate the NMR parameters. The hyperfine contribution to the total paramagnetic NMR (pNMR) chemical shift is shown to be governed by the Fermi-contact (FC) term, and the substituent effect (H vs Br) on the through-bond FC shifts is analyzed, interpreted, and discussed in terms of spin-density distribution, atomic spin populations, and molecular-orbital theory. In contrast to the closed-shell systems of Rh(III), the presence of a single unpaired electron in the open-shell Ru(III) analogs significantly alters the NMR resonances of the ligand atoms distant from the metal center in synergy with the substituent effect.
顺磁过渡金属配合物的分子结构与核磁共振（NMR）参数之间的联系仍相对未被探索。这尤其适用于核磁共振化学位移超精细贡献的接触项。我们报告了将实验 NMR 与相对论密度泛函理论（DFT）相结合，来研究一系列具有 2-取代β-二酮的 Ru(III)配合物。合成了一系列具有系统变化取代基的配合物，并使用 H 和 C NMR 光谱进行分析。在几个温度下记录的 NMR 谱用于构建居里图，并估计对 NMR 位移的温度独立（轨道）和温度相关（超精细）贡献。进行了电子顺磁共振和 NMR 参数的相对论 DFT 计算，以解释实验观察结果。分析和讨论了单个因素（例如基组、密度泛函、精确交换混合和相对论）的影响。基于本工作中的校准研究，选择了完全相对论的 Dirac-Kohn-Sham（DKS）方法、GIAO 方法（轨道位移）、PBE0 功能与三 ζ 价基组以及用于描述溶剂效应的极化连续体模型来计算 NMR 参数。证明总顺磁 NMR（pNMR）化学位移的超精细贡献由费米接触（FC）项控制，并且分析、解释和讨论了取代基（H 对 Br）对通过键 FC 位移的影响，这是基于自旋密度分布、原子自旋密度和分子轨道理论。与 Rh(III)的闭壳系统相反，在开壳 Ru(III)类似物中存在单个未配对电子，与取代基效应协同作用，显著改变了远离金属中心的配体原子的 NMR 共振。
