Prussian blue complex

In the first experiment 10 ml of 500 ppm solutions of FeCl3 were sonicated for 15, 30, 45 and 60 min. To examine the reduction of Fe(III) to Fe(II), 0.1 ml of the sonicated sample was transferred to a 10 ml volumetric flask and mixed with 0.5 ml of 2,000 ppm K3[Fe(CN)6] solution before making up to the mark with distilled water. Final concentration of this sonicated sample in 10 ml of volumetric flask was 5 ppm. UV-vis absorbance at >.max 795 was recorded. Sonication reduced Fe3+ to Fe2+, which reacted with K3[Fe(CN)6], already added in the solution, to form blue colour due to prussian blue. Continuous sonication gradually increased the concentration and intensity of prussian blue complex, as is clear from the Table 10.1. 

This method for determining reducing sugars (7) is based on the reduction of ferricyanide ions in alkaline solution by a reducing sugar. The ferrocyanide produced can then react with a second mole of ferricyanide producing the ferric-ferrocyanide (Prussian blue) complex. Potassium... 

Sato and co-workers presented the first example of the ability to optically change the magnetic field in a single crystal. The magnetic field is a macroscopic property, but the principle behind the switching mechanism is photoinduced electron transfer within the crystalline lattice. Sato and co-workers employed a Prussian Blue complex with the stoichiometry Ko.2Coi,4[Fe(CN)6] 6.9 H2O. It formed the rock-salt... 

The complex formed is highly insoluble (Ksp = 3 x 10-41) (22). Neither iron (III) nor ferricyanide solution absorb at 726 nm. Hence, the use of measured volumes of reagent, and measurement against the corresponding reagent blank gave a linear calibration for the drug. We herefore report the formation and application of the Prussian blue complex in the development of a sensitive spectrophotomet-ric method for the determination of ETD. 

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 ... 

Further ligands that can be bonded by different atoms include OCN- and NG2. Cyanide ions always are linked with their C atoms in isolated complexes, but in polymeric structures as in Prussian blue they can be coordinated via both atoms (Fe—C=N—Fe). 

Extensive work has been carried out on microsensors built from electropolymerized nickel porphyrin films.328,329 Films of Prussian blue (Fe4[Fe(CN)6]3) 345 metal-salen complexes (M = Co, Fe, Cu, Mn)346 or the ferrocene-containing Nin-tetraaza[14] annulene (24),347 also exhibit interesting activity for NO electrooxidation and sensing. 

Except for deposition of Prussian blue from the mixture of ferric and ferricya-nide ions, its electrosynthesis from the single ferricyanide solution is reported [13]. Ferricyanide ions are not extremely stable even in aqueous solution, which is noticed in the change of color after a few days of storage. Thus, the coordination sphere can be destroyed also in the course of electrochemical reactions. The mentioned processes may lead to formation of ferric-ferricyanide complex or free ferric ions. The reduction of the resulting mixture leads to the formation of Prussian blue. 

Solubility data (pA sp) for two dozen hexacyanoferrate(II) and hexacyanoferrate(III) salts, and Pourbaix (pe/pH) diagrams for iron-cyanide-water, iron-sulfide-cyanide-(hydr)oxide, iron-arsenate-cyanide-(hydr)oxide, and iron-copper-cyanide-sulfide-(hydr)oxide, are given in a review ostensibly dedicated to hydrometallurgical extraction of gold and silver. " The electrochemistry of Prussian Blue and related complexes, in the form of thin films on electrodes, has been reviewed. ... 

Such cyanide complexes are also known for several other metals. All the fer-rocyanide complexes may be considered as the salts of ferrocyanic acid H4Fe(CN)e and ferricyanide complexes are that of ferricyanic acid, H3Fe(CN)e. The iron-cyanide complexes of alkali and alkaline-earth metals are water soluble. These metals form yellow and ruby-red salts with ferro-cyanide and ferricyanide complex anions, respectively. A few of the hexa-cyanoferrate salts have found major commercial applications. Probably, the most important among them is ferric ferrocyanide, FeFe(CN)e, also known as Prussian blue. The names, formulas and the CAS registry numbers of some hexacyanoferrate complexes are given below. Prussian blue and a few other important complexes of this broad class of substances are noted briefly in the following sections ... 

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... 

Cobalt(II) hexacyanoferrate, formally similar to Prussian blue, exhibits a far more complex electrochemistry. Only recently, Lezna etal. [65] succeeded in elucidating this system by a combination of in situ infrared spectroscopy and electrochemistry, and ex situ X-ray photoelectron spectroscopy. Figure 8 shows the pathways of the three different phases involved in the electrochemistry, and their interconversion by electrochemical redox reactions and photochemical reactions. 

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