title: Why is N···Be distance of NH3H(+)···DBeH shorter than that of NH3D(+)···HBeH? Paradoxical geometrical isotope effects for partially isotope-substituted dihydrogen-bonded isotopomers.
abstract: 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.
authors: Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido 1-1, Gifu, 501-1193, Japan.
authors: Taro
authors: T
authors: Udagawa
authors: Masanori
authors: M
authors: Tachikawa
mesh_terms: D001608:Beryllium / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D006859:Hydrogen; D003903:Deuterium; D009584:Nitrogen; D001608:Beryllium
keywords: ab initio calculation; dihydrogen-bond; geometrical isotope effect; multicomponent molecular orbital method