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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Relativistic and Electron-Correlation Effects on the Nuclear Magnetic Resonance Shieldings of Molecules Containing Tin and Lead Atoms
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Relativistic and Electron-Correlation Effects on the Nuclear Magnetic Resonance Shieldings of Molecules Containing Tin and Lead Atoms

机译：相对论和电子相关对含锡和铅原子分子的核磁共振屏蔽的影响

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The reference values for NMR magnetic shieldings, σ~(ref), are of the highest importance when theoretical analysis of chemical shifts are envisaged. The fact that the nonrelativistically valid relationship among spin-rotation constants and magnetic shieldings is not any longer valid for heavy atoms requires that the search for σ~(ref) for such atoms needs new strategies to follow. We present here results of σ~(ref) that were obtained by applying our own simple procedure which mixes accurate experimental chemical shifts (δ) and theoretical magnetic shieldings (σ). We calculated σ(Sn) and σ(Pb) in a family of heavy-halogen-containing molecules. We found out that σ~(ref)[Sn;Sn(CH_3)_4] in gas phase should be close to 3864.11 ± 20.05 ppm (0.5%). For Pb atom, σ~(ref)[Pb;Pb(CH_3)_4] should be close to 14475.1 ± 500.7 ppm. Such theoretical values correspond to calculations with the relativistic polarization propagator method, RelPPA, at the RPA level of approach. They are closer to experimental values as compared to those obtained applying few different functionals such as PBE0, B3LYP, BLYP, BP86, KT2, and KT3 of the density functional theory, DFT. We studied tin and lead shieldings of the XY_(4?n)Z_n (X = Sn, Pb; Y, Z = H, F, Cl, Br, I) and PbH_(4?n)I_n (n = 0, 1, 2, 3, 4) family of compounds with four-component functionals as implemented in the DIRAC code. For these systems results of calculations with RelPPA-RPA are more reliable than DFT ones. We argue about why those DFT functionals must be modified in order to obtain more accurate results of NMR magnetic shieldings within the relativistic regime: first, there is a dependence among both electron-correlation and relativistic effects that should be introduced in some way in the functionals; and second, the DIRAC code uses standard nonrelativistic functionals and the functionals B3LYP and PBE0 were parametrized only with data taken from light elements. It can explain why they are not able to properly introduce relativistic effects on nuclear magnetic shieldings. We finally show that in the analysis of magnetic shieldings for the family of compounds mentioned above, one must consider the newest and so-called heavy-atom effect on vicinal heavy atoms, HAVHA. Such effects are among the most important relativistic effects in these kind of compounds.
机译：当设想对化学位移进行理论分析时，NMR磁屏蔽的参考值σ〜（ref）最重要。自旋旋转常数与磁屏蔽之间的非相对论有效关系不再对重原子有效的事实要求对此类原子的σ〜（ref）搜索需要遵循新的策略。我们在此介绍σ〜（ref）的结果，该结果是通过应用我们自己的简单过程获得的，该过程将准确的实验化学位移（δ）和理论磁屏蔽（σ）混合在一起。我们计算了含有重卤素的分子家族中的σ（Sn）和σ（Pb）。我们发现气相中的σ〜（ref）[Sn; Sn（CH_3）_4]应该接近3864.11±20.05 ppm（0.5％）。对于Pb原子，σ〜（ref）[Pb; Pb（CH_3）_4]应该接近14475.1±500.7 ppm。这些理论值对应于相对论极化传播器方法RelPPA在RPA级别的计算。与使用密度函数理论DFT的几种不同功能（例如PBE0，B3LYP，BLYP，BP86，KT2和KT3）获得的结果相比，它们更接近实验值。我们研究了XY_（4？n）Z_n（X = Sn，Pb; Y，Z = H，F，Cl，Br，I）和PbH_（4？n）I_n（n = 0，1 ，2、3、4）的化合物家族具有DIRAC代码中实现的四组分功能。对于这些系统，RelPPA-RPA的计算结果比D​​FT更为可靠。我们争论为什么必须修改那些DFT功能，以便在相对论范围内获得NMR磁屏蔽的更准确结果：首先，在功能中应以某种方式引入电子相关和相对论效应之间的依赖关系;其次，DIRAC代码使用标准的非相对论功能，并且仅使用来自轻元素的数据对功能B3LYP和PBE0进行了参数设置。它可以解释为什么它们不能适当地对核磁屏蔽引入相对论效应。我们最终表明，在对上述化合物家族的磁屏蔽进行分析时，必须考虑到对邻位重原子HAVHA的最新的所谓重原子效应。这些影响是这类化合物中最重要的相对论影响。

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