Prussian blue compounds

K+ is generally used as the reversibly intercalating ion since it leads to insoluble compounds for all the forms. In the mixed-valence Prussian Blue compound, Fe is in the high-spin state and coordinated octahedrally with the N ends of the cyaiudes, whereas Fe is low-spin and octahedrally coordinated with the C ends of the... 

Prussian Blue. Reaction of [Fe(CN)6]4 with an excess of aqueous iron(III) produces the finely divided, intensely blue precipitate Prussian Blue [14038-43-8] (tetrairon(III) tris(hexakiscyanoferrate)), Fe4fFe(CN)6]. Prussian Blue is identical to Turnbull s Blue, the name which originally was given to the material produced by reaction of [Fe(CN)6]3 with excess aqueous iron(II). The solid contains or has absorbed on its surface a laige and variable number of water molecules, potassium ions (if present in the reaction), and iron(III) oxide. The iron(II) centers are low spin and diamagnetic iron(III) centers are high spin. Variations of composition and properties result from variations in reaction conditions. Rapid precipitation in the presence of potassium ion affords a colloidal suspension of Prussian Blue [25869-98-1] which has the approximate composition IvFe[Fe(CN) J. Prussian Blue compounds are used as pigments in inks and paints and its formation on sensitized paper is utilized in the production of blueprints. 

PCPs have infinite networks with backbones constructed by metal ions as connectors and ligands as linkers, and form a family of inorganic and organic hybrid polymers. The structural integrity of the building units, which can be maintained throughout the reactions, allows for their use as modules in the assembly of extended structures. Werner complexes, /3-M(4-melhylpyridyl)4(NCS)2 (M = Ni(II) or Co(II)) [48], Prussian blue compounds [49-51], and Hofmann clathrates and their... 

The CK" ion can act either as a monodentate or bidentate ligand. Because of the similarity of electron density at C and N it is not usually possible to decide from X-ray data whether C or N is the donor atom in monodentate complexes, but in those cases where the matter has been established by neutron diffraction C is always found to be the donor atom (as with CO). Very frequently CK acts as a bridging ligand - CN- as in AgCN, and AuCN (both of which are infinite linear chain polymers), and in Prussian-blue type compounds (p. 1094). The same tendency for a coordinated M CN group to form a further donor-aceeptor bond using the lone-pair of electrons on the N atom is illustrated by the mononuclear BF3 complexes... 

FIGURE 16.16 When potassium cyanide is added to a solution of iron(ll) sulfate, the cyanide ions replace the H.O ligands of the [Fe(H20), - + complex (left and produce a new complex, the hexacyanoferrate(ll) ion, Fe(CN)(l 4 (right). The blue color is due to the polymeric compound called Prussian blue, which forms from the cyanoferrate ion. 

Originally, compounds containing coordination complexes were given common names such as Prussian blue (KFe[Fe (CN)g ]), which is deep blue, or Reinecke s salt (NH4[Cr (NH3)2 (NCS)4]), named for its first maker. Eventually, coordination compounds became too numerous for chemists to keep track of all the common names. To solve the nomenclature problem, the International Union of Pure and Applied Chemistry (lUPAC) created a systematic procedure for naming coordination compounds. The following guidelines are used to determine the name of a coordination compound from its formula, or vice versa ... 

Other Inorganic Compounds Prussian Blue represents another type of inorganic mixed valence electrochromic materials. This material is known in three states ... 

In the literature the term soluble Prussian blue introduced by Keggin and Miles [5] to determine the KFeFe(CN)6 compound is still widely used. However, it is important to note, that the term soluble refers to the ease with which the potassium ion can be peptized rather than to the real solubility of Prussian blue. Indeed, it can be easily shown by means of cyclic voltammetry that the stability of Prussian blue films on electrode supports is nearly independent of their saturation by potassium cations. Moreover, Itaya and coworkers [9] have not found any appreciable amount of potassium ions in Prussian blue, which makes doubtful structures like KFeFe(CN)6. Thus, the above equation fully describes the Prussian blue/Prussian white redox reaction. 

In contrast to a variety of oxidizable compounds, only a few examples for the detection of strong oxidants with transition metal hexacyanoferrates were shown. Among them, hydrogen peroxide is discussed in the following section. Except for H202, the reduction of carbon dioxide [91] and persulfate [92] by Prussian blue-modified electrode was shown. The detection of the latter is important in cosmetics. It should be noted that the reduction of Prussian blue to Prussian white occurs at the lowest redox potential as can be found in transition metal hexacyanoferrates. 

J.E Keggin and F.D. Miles, Structure and formulae of the Prussian blue and related compounds. Nature 137, 577-578 (1936). 

Other well-known compounds that exist with a mixed valence are Prussian blue [Fe3+[Fen (CN)64-]], and ferre-doxin, in which iron has the valence of +11 and -Fill. 

Figure 8.3 shows a set of spectra of Prussian Blue generated at an ITO electrode. Prussian Blue is the mixed valence compound, K+(Fe " "[Fe"(CN)6]). The colour formed, as shown by the increasing absorbance in the figure, represents the generation of coloured Prussian Blue from the colourless Everitt s salt, K2Fe2+[Fe"(CN)6]. 

Metal hexacyanoruthenates possess a lower symmetry. Several compounds have highly disordered structures, especially when no alkali cations are present for charge compensation. Such a complex defect structure has been found for a completely potassium free Prussian blue precipitated very slowly from a solution in concentrated hydrochloric acid [25, 26]. Here, the structure still remains cubic face-centered however, one-third of the [M1 -1(CN)6] is vacant, randomly distributed and that space is filled with water molecules. The coordination sphere of the remaining ions is maintained... 

The electrodes modified by hexacyano-ferrates compounds were also used as voltammetric sensors [409-412]. The cadmium hexacyanoferrate-based composite ion-sensitive electrode for voltammetry was explored by Scholz and coworkers [409]. The potential of such electrode depends linearly on the logarithm of concentration of alkali and alkaline-earth metals ions in the solutions. Bo and fin have studied [410] Prussian blue (PB)/Pt modified electrode in GdGh electrolyte by cyclic voltammetry and in situ Fourier transform IR spectroscopy (FTIR) spectro-electrochemistry. Cadmium hexacyanofer-rates were formed on a PB film. 

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