The solvation structure of fulleride C605- anions in potassium ammonia solution

The solvation of the fulleride anion C-60(5-) 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 C-60(5-) has two distinct solvation shells containing similar to 45 and similar to 80 ammonia molecules at distances of similar to 6.6 and similar to 9.5 angstrom, respectively. This solvation effectively doubles the fulleride radius to similar 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.