Neutron Diffraction Studies on the Hydrogen-Bonded Structure of Water Molecules in Ion Exchange Resins

Neutron diffraction measurements were carried out for anion and cation exchange resins (AER and CER, respectively) absorbing H/D isotopically substituted water molecules in order to obtain structural information on the hydrogen-bonded network among water molecules within the resins. Partial structure factors, aHH(Q), aXH(Q), and aXX(Q) (X: atoms involved in the sample except for water-hydrogen atom), for AER and CER samples were respectively deduced from combined analyses of intermolecular interference terms observed for resins containing D2O (99.8% D), 0H2O (35.9% D), and 0–2H2O (67.9% D). The nearest neighbor distances, r(O···H) = 1.95(3) Å and r(H···H) = 2.40(3) Å, determined for the AER sample agree well with those reported for pure liquid water. On the other hand, considerably shorter intermolecular distances, r(O···H) = 1.78(3) Å and r(H···H) = 2.28(3) Å, were found for the CER sample, implying that the hydrogen-bonded network among water molecules in CER would be strongly affected by a highly acidic environment.