Cover of the Journal of Physical Chemistry - April 14, 2007

An article written by researchers at the London Centre for Nanotechnology and UCL's Physics and Astronomy Department is the cover of issue 111 of the Journal of Physical Chemistry, published on the 14th April 2007.


The article is available for download.

Title: The Solvation Structure of Fulleride C605- Anions in Potassium Ammonia Solution

Authors:
Christopher A. Howard, Jonathan C. Wasse and Neal T. Skipper
London Centre for Nanotechnology, Department of Physics and Astronomy, University College London
Helen Thompson and Alan K. Soper
ISIS Facility, Rutherford Appleton Laboratory


Abstract:
The solvation of the fulleride anion C605- has been studied in concentrated potassium-ammonia solution using
advanced neutron diffraction techniques.

Isotopic substitution of hydrogen for deuterium in conjunction with second-order difference analysis has allowed us to obtain a detailed picture of the solvent structure. Because of the complexity of our system, we have visualized this structure via empirical potential structural refinement. This method provides us with a full three-dimensional molecular model of our system that is consistent with the experimental data.

The results reveal the way in which hydrogen bonds between the solvent and solute assemble to accommodate high concentrations of monodisperse fulleride anions in solution. We find that each C605- has two distinct solvation shells containing ∼45 and ∼80 ammonia molecules at distances of ∼6.6 and ∼9.5 Angstrom, respectively. This solvation effectively doubles the fulleride radius to ∼10.5 Angstrom. Within the first solvation shell, each ammonia molecule forms an average of around one hydrogen bond to the fulleride anion, thereby allowing for intersolvent hydrogen bonding to be maintained. We find that the potassium cations are solvated by approximately six ammonia molecules at an average distance of around 2.87 Angstrom. This is consistent with the solvation observed in bulk metal-ammonia solutions. This work therefore highlights the mechanisms by which metal-ammonia solutions are able to dissolve high concentrations of fullerenes.

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