Prussian Blue analogues

J.M. Zen, A.S. Kumar, and H.W. Chen, Electrochemical behavior of stable cinder/Prussian blue analogue and its mediated nitrite oxidation. Electroanalysis 13, 1171-1178 (2001). 

Table 5 Compositions and iron oxidation states in cobalt-iron Prussian Blue analogues Na cCo Fe(CN)6-zH20. ...

The thermal decomposition of a number of double complexes containing the [Cr(CN)6]3-anion has been investigated and the results obtained under quasi-isothermal and -isobaric conditions are summarized in Scheme 31.336 The CN-flipping reactions involved in the scheme resemble similar reactions of Prussian blue analogues such as Co3[Cr(CN)6]2 337 and Fe3[Cr(CN)6]2-338 The unusually low magnetic moment of Cr(CN)6Cr indicates considerable metal-metal interaction via the CN bridges. 

An additional family of organometallic materials is the cyanometallates, which are Prussian blue analogues. These are microporous materials, similar to zeolites, with relatively large adsorption space and small access windows [237-241], These Prussian blue analogues develop zeolite-like structures based upon a simple cubic (T[M(CN)6]) framework, in which octahedral [M(CN)6]" complexes are linked via octahedrally coordinated, nitrogen-bound Tm+ ions [237], In the prototypic compound, that is, Prussian blue, specifically (Fe4[Fe(CN)6]3 14H20), charge balance with the Fe3+ ions conducts to vacancies at one-quarter of the [Fe(CN)6]4 complexes [242],... 

Because of their properties they are widely used in electrochemistry, in electrophotography, as well as in photocatalysis and photochemical water cleavage. Thus Hennig and Rehorek in 1986 reported the sensitization of photochemical reactions by Prussian blue analogues of molybdenum octacyanide, and Kaneko and his group in 1984 found that water can be photolyzed with visible light in presence of Pmssian blue and tris (2, 2 -bipyridine) ruthenium (II) complex. 

Rasmussen, P.C. and Meyers, E.A. 1984. An investigation of Prussian blue analogues by Mossbauer spectroscopy and magnetic susceptibility. Polyhedron, 3,183-190. 

Figure 2 Three-dimensional cubic structure of an idealised Prussian blue analogue.

Although the magnetisation of the Prussian blue analogues is very small, since room temperature has been reached it is now possible to find applications for these... 

The Prussian blues are not truly molecular but molecular-based, at the border between molecular and solid-state chemistry. They present many vacancies and defects and are often mixtures. Nevertheless, it is inspiring that one of the oldest coordination compounds is providing such a stir in solid-state chemistry. Since the main features of the Prussian blue analogues are becoming increasingly understood, chemists have now begun to explore other directions. 

State. When both iron environments contain only iron(II), the resulting salt is not colored (Prussian White). The oxidation state localization in PB has been studied extensively. Structures, electrochemical behavior (electrodes batteries), and uses in medicine (treatment of Cs and of thallium poisoning) of Prussian Blue are mentioned in a review of cyanide complexes. In cobalt-iron Prussian Blue analogues, NaxCo3,Fe(CN)6-zH20 electronic and spin states are controlled by temperature and the ligand field strength around the Co + ions, which in turn is determined by the Co Fe ratio. ... 

Figure 2.13 Unit cell of the Prussian blue analogue structure Ma[Mb(CN)6] where the red, black, white and blue spheres represent Ma, Mb, C and N, respectively [16], Copyright (2007), with permission of Elsevier.

The importance of the pore size in Prussian blue analogues is supported by differential pair distribution function analysis of X-ray and neutron scattering data of hydrogen- and deuterium-loaded Mn3[Co(CN)6]2 [119]. This shows that no evidence for adsorption interactions with unsaturated metal sites exists and that the hydrogen molecules are disordered about the center of the pores defined by the cubic framework. In conclusion, experimental results indicate that optimum pore dimensions in Prussian blue analogues are predominantly responsible for the heat of adsorption at low loadings rather than the polarizing effect of open metal sites. 

Prussian Blue, Fe4[Fe(CN)6]3-14H20, has been known for three centuries, and its crystal structure (Buser et al., 1977) incorporates octahedral Fe(II) centres bound to six cyanide ligands in a [Fe(CN)6] moiety. The terminal N-donors of the cyanide ligands point to additional Fe(III) centres and a charge-balance of four Fe(IIl) centres with three [Fe(CN)6]" anions is achieved. Six of the 14 water molecules are bound to Fe(lll) and the remaining 8 fill the void in the framework structure and can be removed by heat treatment in vacuo. A wide variety of Prussian Blue analogues M c[MXCN)6]3,-zH20 [M... 

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