Vícha Jan, Novotný Jan, Straka Michal, Repisky Michal, Ruud Kenneth, Komorovsky Stanislav, Marek Radek
CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic.
Phys Chem Chem Phys. 2015 Oct 14;17(38):24944-55. doi: 10.1039/c5cp04214c.
The role of various factors (structure, solvent, and relativistic treatment) was evaluated for square-planar 4d and 5d transition-metal complexes. The DFT method for calculating the structures was calibrated using a cluster approach and compared to X-ray geometries, with the PBE0 functional (def2-TZVPP basis set) providing the best results, followed closely by the hybrid TPSSH and the MN12SX functionals. Calculations of the NMR chemical shifts using the two-component (2c, Zeroth-Order Regular Approximation as implemented in the ADF package) and four-component (4c, Dirac-Coulomb as implemented in the ReSpect code) relativistic approaches were performed to analyze and demonstrate the importance of solvent corrections (2c) as well as a proper treatment of relativistic effects (4c). The importance of increased exact-exchange admixture in the functional (here PBE0) for reproducing the experimental data using the current implementation of the 2c approach is partly rationalized as a compensation for the missing exchange-correlation response kernel. The kernel contribution was identified to be about 15-20% of the spin-orbit-induced NMR chemical shift, ΔδSO, which roughly corresponds to an increase in ΔδSO introduced by the artificially increased exact-exchange admixture in the functional. Finally, the role of individual effects (geometry, solvent, relativity) in the NMR chemical shift is discussed in selected complexes. Although a fully relativistic DFT approach is still awaiting the implementation of GIAOs for hybrid functionals and an implicit solvent model, it nevertheless provides reliable NMR chemical shift data at an affordable computational cost. It is expected to outperform the 2c approach, in particular for the calculation of NMR parameters in heavy-element compounds.
对平面四方的4d和5d过渡金属配合物评估了各种因素（结构、溶剂和相对论处理）的作用。使用簇方法校准了用于计算结构的DFT方法，并与X射线几何结构进行了比较，PBE0泛函（def2-TZVPP基组）给出了最佳结果，紧随其后的是混合TPSSH和MN12SX泛函。使用双组分（2c，ADF软件包中实现的零阶正则近似）和四组分（4c，ReSpect代码中实现的狄拉克-库仑）相对论方法进行了NMR化学位移计算，以分析和证明溶剂校正（2c）以及相对论效应的适当处理（4c）的重要性。在使用当前2c方法实现时，泛函（此处为PBE0）中增加的精确交换混合对于重现实验数据的重要性，部分原因被认为是对缺失的交换相关响应核的补偿。确定核贡献约为自旋轨道诱导的NMR化学位移ΔδSO的15 - 20%，这大致对应于泛函中人为增加的精确交换混合所引入的ΔδSO的增加。最后，在选定的配合物中讨论了各个效应（几何结构、溶剂、相对论）在NMR化学位移中的作用。尽管完全相对论性的DFT方法仍在等待用于混合泛函和隐式溶剂模型的GIAOs的实现，但它仍然能够以可承受的计算成本提供可靠的NMR化学位移数据。预计它将优于2c方法，特别是在重元素化合物的NMR参数计算方面。
