Is the Hexacyanoferrate(II) Anion Stable in Aqueous Solution? A Combined Theoretical and Experimental Study

Abstract

A combined theoretical and experimental study has been performed to elucidate the structural and dynamical properties of aqueous hexacyanoferrate(II) isolated and in presence of potassium ions. It is shown that in absence of counter ions, the highly negatively charged hexacyanoferrate(II) complex is not stable in aqueous solution.However, if the high negative charge is compensated by potassium counter ions, a stable complex is observed, which is proven by theoretical simulations as well as by EXAFS experiments. From the simulation it is found that potassium ions surrounding the complex are highly mobile and thus, cannot be observed in the experiment. The structure of aqueous hexacyanoferrate(II) in 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 should be the reason for the very short hydrogen bond lifetimes in the femtosecond range of the cyanide ligands.

Comprehensive Experimental and Computational Spectroscopic Study of Hexacyanoferrate Complexes in Water: From Infrared to X-ray Wavelengths

“…The differences in line width are attributed to the stronger interactions of the ferrous species with the solvent shell, as discussed above (Figure 1) and in previous studies. 2,3,7,14 The stronger interaction with the water molecules for the Fe(II) complex in comparison with the Fe(III) species results in a larger structural heterogeneity for the former in solution. For example, in Figure 1c, we note that the distribution of g(r) for the CN bond lengths is greater in the ferrous complex than the ferric one, which is a result of stronger hydrogen bonding interactions of the cyanide ligands with the water molecules.…”

Electrodeposition of Prussian Blue/Carbon Nanotube Composites at a Liquid‑Liquid Interface

“…61,62 Even though it can decompose under high exposure to UV light, if in high concentration, the timescale of decomposition is far longer than the electrodeposition of PB, especially in the mmol L -1 range used in these experiments. 63 Yet, its decomposition does not generate free iron species, which are responsible for PB formation in the case of K 3 [Fe(CN) 6 ].…”

Nanometer patterning of water by tetraanionic ferrocyanide stabilized in aqueous nanodrops

“…During the simulation, the Fe–C force constants were increased in order to avoid cyano ligand loss, which does not occur experimentally for nanodrops of this size, but has been observed previously in QM/MM simulations. 48 The ion was not confined to the center of the aqueous cluster during the dynamics trajectories. An initial geometry relaxation was performed followed by equilibration with a 1 ns stochastic dynamics trajectory at 133 K using the OPLS 2005 force field with 1.0 fs time steps.…”

“…42–44 Experiments on this ion in water have revealed a distinct inner solvation shell around ferrocyanide, but no information has been reported about how this anion influences the structure of water beyond the first solvation shell. 45–48 The direct measurement of extended ion–water interactions by an individual tetraanionic species is not feasible in the condensed phase due to the low concentrations necessary for hydration shells to exist unperturbed by counterions. However, the stability afforded by aqueous gas phase clusters and the sensitivity of IRPD spectroscopy to the orientation of surface water molecules provide a well-suited method for studying this high charge density tetraanion.…”