Proton and Deuteron NMR Study on Single Crystals of Na2ZnCl4 · 3 H2O (Na2ZnCl4 · 3 D2O)

Abstract

Single crystal 1H- and 2H-XMR spectra of Na2ZnCl4 · 3 H2O and Xa2ZnCl4 · 3 D2O, respectively, were studied. The following results have been obtained: The positions of the hydrogens and deuterons are described in the space group C2 3v- P 31m with one formula unit in the unit cell. The point positions are: HI(DI) in 3m: x = 0.455 ± 4, y = 0, z = 0.556 ± 5; HII(DII) in 3m: x = 0.675 ± 4, y = 0, z = 0.466 ± 5. The angle H-O -H (D-O-D) is 107.0° and the H-H distance is 1.603 + 3 Å. Including dynamical corrections, the equilibrium positions are: HI(DI) : x = 0.459 ± 4, y - 0, z = 0.550 ± 5; HII(DII): x = 0.669 ± 4, y = 0, z = 0.464 ± 5. The H-H distance is then 1.537 ± 5 Å. From the 2H-NMR the nuclear quadrupole coupling constant of the deuterons is at T = 22 °C: e2qQ/h = 132.0 ± 1.0 kHz; η = 0.754 ± 5. The major principal axis of the electric field gradient tensor is perpendicular to the twofold axis of the molecule D2O. At T = -25 °C for the two deuteron atoms of one molecule D2O, the values (e2qQ/h)I = 239.7 ± 1.0 kHz; ηI = 0.118 ± 2; (e2qQ/h)II = 235.9 ± 1.0 kHz; ηII = 0.125 ± 2 have been found. Here the intermediate principal axis of the FGT is perpendicular to the H-O-H plane. The direction cosines of the FGTs have been determined. The activation energy for the flipping process was found to be 12.7 kcal. mol-1. The possible hydrogen bonds O-H…Cl are discussed.