Olejniczak Malgorzata, Pecul Magdalena
Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
Chemphyschem. 2009 Jun 2;10(8):1247-59. doi: 10.1002/cphc.200800817.
Relativity matters: Calculations of NMR shielding tensors and spin-spin coupling constants transmitted through Ir-H...H-N dihydrogen bonds are presented. The picture shows one of the simplified models employed. It is shown that the spin-orbit relativistic effects influence the NMR shielding constants far more than the spin-spin coupling constants.We present calculations of NMR shielding tensors and spin-spin coupling constants transmitted through Ir-H...H-N dihydrogen bonds. For this purpose, three six-coordinated complexes of iridium have been selected as models of heavy metal complexes and their NMR properties have been calculated within the DFT-ZORA (density functional theory zeroth-order regular approximation) methodology. The influence of intramolecular interactions between hydrogen atoms from IrH(3) and NH(2) groups (including both single dihydrogen bonding and bifurcated hydrogen bonding) on the NMR properties is discussed and the results are compared with the experimental observations. In complexes where dihydrogen bonding occurs, the calculated value of "through-space" (1h)J(H(a)H(b)) is in the range 1.6-7.9 Hz [depending on the model, but with R(H(a)-H(b))<2.0 A], while the experimental values are 2-5 Hz for similar H(a)--H(b) distances. The (2h)J(NH) coupling is also sizeable, ranging from approximately -5.1 Hz for dihydrogen bonds of 2 A up to -7.1 Hz for very short (1.6 A) dihydrogen bonds, and should therefore be experimentally accessible when using (15)N-labelled compounds. The dihydrogen-bond transmitted spin-spin coupling constants (1h)J(HH) and (2h)J(NH) and the shielding tensor of the H(a) atom are the most sensitive probes of the H(a)-H(b) distance, which potentially makes them attractive tools to determine the structure of molecules. The main conclusions are qualitatively similar to those drawn from nonrelativistic calculations in small inorganic complexes, and the spin-orbit relativistic effects influence the NMR shielding constants far more than the spin-spin coupling constants.
本文给出了通过Ir-H…H-N双氢键传递的核磁共振屏蔽张量和自旋-自旋耦合常数的计算结果。图中展示了所采用的一种简化模型。结果表明，自旋-轨道相对论效应相比自旋-自旋耦合常数对核磁共振屏蔽常数的影响要大得多。我们给出了通过Ir-H…H-N双氢键传递的核磁共振屏蔽张量和自旋-自旋耦合常数的计算结果。为此，选择了三种六配位铱配合物作为重金属配合物的模型，并在DFT-ZORA（密度泛函理论零阶正则近似）方法内计算了它们的核磁共振性质。讨论了来自IrH(3)和NH(2)基团的氢原子之间的分子内相互作用（包括单双氢键和分叉氢键）对核磁共振性质的影响，并将结果与实验观测值进行了比较。在发生双氢键的配合物中，“空间”(1h)J(H(a)H(b))的计算值在1.6 - 7.9 Hz范围内[取决于模型，但R(H(a)-H(b))<2.0 Å]，而对于相似H(a)--H(b)距离，实验值为2 - 5 Hz。(2h)J(NH)耦合也相当可观，对于2 Å的双氢键，其值约为 -5.1 Hz，对于非常短的（1.6 Å）双氢键，可达 -7.1 Hz，因此当使用(15)N标记的化合物时，应该可以通过实验检测到。双氢键传递的自旋-自旋耦合常数(1h)J(HH)和(2h)J(NH)以及H(a)原子的屏蔽张量是H(a)-H(b)距离最敏感的探针，这可能使它们成为确定分子结构的有吸引力的工具。主要结论在定性上与从小型无机配合物的非相对论计算得出的结论相似，并且自旋-轨道相对论效应相比自旋-自旋耦合常数对核磁共振屏蔽常数的影响要大得多。
