The solvation of cations in hydrogen-bonded molecular solvents: A neutron diffraction study on the structure of Ni2+ solutions in ethylene glycol and in glycerol

S. Erol Okan, Philip S. Salmon, David C. Champeney, Ingrid Petri

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The method of isotopic substitution in time-of-flight neutron diffraction is used to measure the coordination environment of Ni2 + in both a 0-956 molal solution of Ni(CF3SO3)2 in fully deuterated ethylene glycol (EG) and a 0-980 molal solution of Ni(CF3SO3)2 in fully deuterated glycerol. The results show that EG acts as a bidentate ligand to form [Ni(EG)3]2 + tris-chelate complexes, and are consistent with glycerol acting as a tridentate ligand to form [Ni(glycerol)2]2+ bis-chelate complexes, although bidentate coordinating behaviour with respect to the Ni2 + ion cannot be ruled out. There is no evidence of inner sphere complexing by the CF3SO3 anion in either solution, but the data are consistent with a spatially well defined hydrogen bond O—D…O of length 1-8(1) Å between the hydroxyl groups of the solvent molecules in the first and second coordination shells of the cation. The number of second shell hydroxyl groups that participate in this hydrogen bond process is estimated at six in both solutions. The structural results for the Ni2+ complexes are used to give a qualitative account of the mobility of these entities in the infinite dilution limit, but the hydrodynamic theory of Zwanzig does not give a sphere radius that is in agreement with the complex radius obtained microscopically from the neutron diffraction experiments. The intermediate range ordering in both solutions can be traced to the arrangement of the Ni2+ complexes which are distributed in a way that maximizes their mean separation. A comparison is made between the results obtained for the EG solution by using steady-state and pulsed neutron source instrumentation.

Original languageEnglish
Pages (from-to)325-343
Number of pages19
JournalMolecular Physics
Issue number2
Publication statusPublished - 10 Feb 1995

ASJC Scopus subject areas

  • Biophysics
  • Molecular Biology
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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