NMR Research Unit, University of Oulu, P.O. Box 3000, FI-90014 Oulu, Finland.
Phys Chem Chem Phys. 2018 Sep 12;20(35):22547-22555. doi: 10.1039/c8cp04123g.
Transition metal complexes can possess a large magnetic susceptibility anisotropy, facilitating applications such as paramagnetic tags or shift agents in nuclear magnetic resonance (NMR) spectroscopy. Due to its g-shift and zero-field splitting (ZFS) we demonstrate on a Co(ii) clathrochelate with an aliphatic 16-carbon chain, a modern approach for ab initio calculation of paramagnetic susceptibility. Due to its large anisotropy, large linear dimension but relatively low number of atoms, the chosen complex is especially well-suited for testing the long-range point-dipole approximation (PDA) for the pseudocontact shifts (PCSs) of paramagnetic NMR. A static structure of the complex is used to compare the limiting long-distance PDA with full first-principles quantum-mechanical calculation. A non-symmetric formula for the magnetic susceptibility tensor is necessary to be consistent with the latter. Comparison with experimental shifts is performed by conformational averaging over the chain dynamics using Monte Carlo simulation. We observe satisfactory accuracy from the rudimentary simulation and, more importantly, demonstrate the fast applicability of the ab initio PDA.
过渡金属配合物可以具有较大的磁各向异性，有利于顺磁标记或核磁共振（NMR）光谱中的位移试剂等应用。由于其 g 位移和零场分裂（ZFS），我们以具有脂肪族 16 个碳原子链的 Co(ii) 笼形配合物为例，展示了一种用于顺磁磁化率从头算计算的现代方法。由于其各向异性大、线性尺寸大但原子数量相对较少，所选配合物特别适合测试顺磁 NMR 的赝接触位移（PCSs）的远程点偶极近似（PDA）。使用配合物的静态结构将限制的远距离 PDA 与全第一性原理量子力学计算进行比较。为了与后者保持一致，需要使用非对称的磁化率张量公式。通过使用蒙特卡罗模拟对链动力学进行构象平均来进行与实验位移的比较。我们从基本模拟中观察到令人满意的准确性，更重要的是，证明了从头算 PDA 的快速适用性。
