Ferrocyanides constitution

Potassium ferrocyanide, K4[Fe(CN)6] 3H20 occurs as a trihydrate. The compound is a spin-paired diamagnetic complex in which the ferrocyanide anion constitutes the Fe2+ ion, octahedrally coordinated with six CN ions. It is a yellow monoclinic crystaUine sohd density 1.85 g/cm decomposes at 60°C and soluble in water but insoluble in alcohol and ether. 

A paradigmatic example is provided by an extensively used pigment Pmssian blue— potassium-iron(III) hexacyanoferrate(II), also called potassium-iron(III) fer-rocyanide. This is constituted by potassium-iron(III) ferrocyanide, KFe[Fe(CN)g], whose electrochemistry has been extensively studied [74-77],... 

Experiment Prepare a solution of a ferrous salt by dissolving 2 grams of ferrous ammonium sulphate in 20 cc. of water, adding a little dilute sulphuric acid and a piece of iron wire. Test both this solution and a solution of a ferric salt (nitrate or chloride) with potassium ferrocyanide, potassium ferricyanide, and potassium sulphocyanate. Tabulate the results. These constitute the standard tests for ferrous and ferric salts. Write equation. 

Emschwiller, G. Infrared Spectra of Ferrocyanides and Ferricyanides and Constitution of Prussian Blue. Compt. rend. 238, 1414 (1954). 

Structure and Constitution of Some Ferrocyanides. Gazz. chim. Ital. 68, 803 (1938). 

The constitution of hydrogen and alkali ferrocyanides has for many years been a matter of dispute. Both Graham and Erlenmeyer1 believed that the cyanogen radicles were present m groups of three, as in cyanuric acid, C3N3(OH)3, so that the formula for hydrogen ferro-cyanide becomes —... 

It is, however, to be pointed out that this simplified picture constitutes at the utmost a rough approximation to the real situation. In fact, a close examination of reorganization energies, derived from different series of experimental data shows large differences between X values of various ions and even between those concerning the same ionic species. Thus, for instance, the values of X mentioned in the literature for the ferricyanide/ferrocyanide redox couple vary from 0.4 to about 1.2... 

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