Direct Determination of Intramolecular Structure of D2O in the First Hydration Shell of Ni2+

Time-of-flight (TOF) neutron diffraction measurements have been carried out for aqueous 6 mol% NiCl2 solution in D2O in order to obtain experimental information on intramolecular structure of D2O molecules involved in the first hydration shell of Ni2+. The O-D bond length, r(g OD) = 0.982 +/- 0.002 angstrom has been determined through the least squares fitting analysis of the observed difference interference term between the NiCl2 solution and pure D2O in the high-Q region (14 <= Q <= 40 angstrom(-1)). The present O-D bond length is significantly longer than that determined for pure liquid D2O (r(g OD) (=) 0.978 +/- 0.001 angstrom), confirming strong hydrogen bonds between D2O molecules in the first- and the second hydration shell of Ni2+. These results are in good agreement with the v(OD)-r(OD) relationship obtained from infrared spectra for uncoupled O-D stretching frequency of HDO and O-D bond length of D2O molecule in aqueous solutions determined by neutron diffraction.