Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido 1-1, Gifu, 501-1193, Japan.
J Comput Chem. 2014 Feb 5;35(4):271-4. doi: 10.1002/jcc.23505. Epub 2013 Dec 9.
The partial isotope substitution for the change of geometrical parameters, interaction energies, and nuclear magnetic shielding tensors (σ) of dihydrogen-bonded NH3X(+)···YBeH (X, Y = H, D, and T) systems is analyzed. Based on the theoretical calculation, the distance between heavy atoms RN···Be of NH3H(+) ···DBeH is clearly found to be shorter than that in NH3D(+)···HBeH. Such apparently paradoxical geometrical isotope effect (GIE) on RN···Be is revealed by the cooperative effect of two kinds of (1) primary covalent-bonded GIE and (2) secondary dihydrogen-bonded one. We have demonstrated that (1) the covalent bond lengths become shorter by heavier isotope-substitution and (2) the dihydrogen-bonded distance RX···Y becomes shorter by heavier Y and lighter X isotope-substitution due to the difference of electronic structure reflected by the nuclear distribution. We have also found that interaction energy of NH3H(+)···DBeH is stronger than that of NH3D(+)···HBeH and isotopic deshielding effect of magnetic shielding becomes large in lighter isotope.
对改变几何参数、相互作用能和氢键 NH3X(+)···YBeH (X，Y=H，D 和 T) 体系核磁共振屏蔽张量 (σ) 的部分同位素取代进行了分析。基于理论计算，明显发现 NH3H(+)···DBeH 中 RN···Be 与重原子之间的距离短于 NH3D(+)···HBeH。这种明显的几何同位素效应 (GIE) 是由两种 (1) 主要的共价键 GIE 和 (2) 次级氢键的协同作用引起的。我们已经证明 (1) 较重的同位素取代导致共价键长度变短，(2) 由于核分布反映的电子结构的差异，RX···Y 的氢键距离变短。我们还发现 NH3H(+)···DBeH 的相互作用能强于 NH3D(+)···HBeH，较轻同位素的磁屏蔽去屏蔽效应较大。
