H/D isotope effect on charge-inverted hydrogen-bonded systems: Systematic classification of three different types in H3XH···YH3 (X = C, Si, or Ge, and Y = B, Al, or Ga) with multicomponent calculation.

Abstract

Three different H/D isotope effect in nine H3 XH(D)···YH3 (X = C, Si, or Ge, and Y = B, Al, or Ga) hydrogen-bonded (HB) systems are classified using MP2 level of multicomponent molecular orbital method, which can take account of the nuclear quantum nature of proton and deuteron. First, in the case of H3 CH(D)···YH3 (Y = B, Al, or Ge) HB systems, the deuterium (D) substitution induces the usual H/D geometrical isotope effect such as the contraction of covalent R(C-H(D)) bonds and the elongation of intermolecular R(H(D)···Y) and R(C···Y) distances. Second, in the case of H3 XH(D)···YH3 (X = Si or Ge, and Y = Al or Ge) HB systems, where H atom is negatively charged called as charge-inverted hydrogen-bonded (CIHB) systems, the D substitution leads to the contraction of intermolecular R(H(D)···Y) and R(X···distances. Finally, in the case of H3 XH(D)···BH3 (X = Si or Ge) HB systems, these intermolecular R(H(D)···Y) and R(X···Y) distances also contract with the D substitution, in which the origin of the contraction is not the same as that in CIHB systems. The H/D isotope effect on interaction energies and spatial distribution of nuclear wavefunctions are also analyzed.