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Is the Hexacyanoferrate(II) Anion Stable in Aqueous Solution? A Combined Theoretical and Experimental Study
Andreas O Tirler1, Ingmar Persson2, Thomas S Hofer1
1Theoretical Chemistry Division Institute of General, Inorganic and Theoretical Chemistry University of Innsbruck , Innrain 80-82, A-6020 Innsbruck, Austria.
Abstract:
A combined theoretical and experimental study was performed to elucidate the structural and dynamical properties of the isolated aqueous hexacyanoferrate(II) ion as well as in the presence of potassium counterions. It is shown that in absence of counterions, the highly negatively charged hexacyanoferrate(II) complex is not stable in aqueous solution. However, if the high negative charge is compensated by potassium counterions, a stable complex is observed, which is proven by theoretical simulations as well as by extended X-ray absorption fine structure (EXAFS) experiments. From the simulation it is found that potassium ions surrounding the complex are highly mobile and thus cannot be observed via EXAFS experiments. The structure of aqueous hexacyanoferrate(II) in the presence of potassium ions is identical to that of the solid-state structure, but the mobility of potassium ions is significantly increased in the liquid. These highly mobile potassium ions circulating the complex are the reason for the very short lifetime of hydrogen bonds between solvent water molecules and cyanide ligands being on the femtosecond scale.
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