A neutron diffraction study on the structure of Cl^- solutions in hydrogen-bonded molecular solvents

The method of isotopic substitution in time-of-flight neutron diffraction is applied to measure the coordination environment of Cl^- in a 0.999(2) molal solution of NaCl in fully deuterated glycerol. It is shown that the glycerol molecules act as monodentate ligands to give a Cl(glycerol) complex that comprises Cl^-...D-O hydrogen bonds, which are approximately linear and of length 2.17(3) AA. The results are compared with those obtained for the solvation of Cl^- in solutions of its salts in water, methanol and ethylene glycol (EG). A reduction from approximately six (water) to four (methanol and EG) to three (glycerol) is found for the Cl^-solvation number as the solvent is changed and, for all four solvents, the Cl ^-...D-O hydrogen bond is typically linear.