- Prussian blue
Name = Prussian blue
ImageFile = Prussian blue.jpg
ImageSize = 250px
ImageName = A sample of Prussian blue
ImageSize1 = 250px
IUPACName = Ferric hexacyanoferrate
OtherNames = ferric ferrocyanide, iron(III)
ferrocyanide, iron(III) hexacyanoferrate(II), ferric hexacyanoferrate (German: "Preußischblau" and "Berliner Blau", Berlin blue
Section1 = Chembox Identifiers
CASNo = 14038-43-8
RTECS = V03AB31
Section2 = Chembox Properties
Formula = Fe7(CN)18(H2O)x
MolarMass = 859.23 g/mol
Appearance = blue solid
Solubility = insoluble
Section3 = Chembox Structure
Section7 = Chembox Hazards
Section8 = Chembox Related
Prussian blue is a very dark blue, colorfast, non-toxic
pigment– one of the first synthetic dyes – which was discovered accidentally in Berlin in 1704. Its name comes from the fact that it was first extensively used to dye the dark blue uniforms of the Prussian army. [http://www.sewanee.edu/chem/Chem&Art/Detail_Pages/Pigments/Prussian_Blue Website of The University of the South, Sewanee] Another name for the color "Prussian blue" is "Berlin blue".
It is an
inorganic compoundwith the idealized formula Fe7(CN)18, containing also variable amounts of water and other ions. With several other names (see table to right), this dark bluesolid is commonly abbreviated "PB."*Dunbar, K. R. and Heintz, R. A., "Chemistry of Transition Metal Cyanide Compounds: Modern Perspectives", Progress in Inorganic Chemistry, 1997, 45, 283-391.] PB is a common pigment, the object of instructional experiments, and an antidotefor certain kinds of heavy metal poisoning. Because it is easily synthesized in impure form, it also has a complicated chemistrythat has led to extensive speculation on its structure. It is used in paints and is the "blue" in blueprints.
Prussian blue was discovered accidentally [http://painting.about.com/cs/colourtheory/a/prussianblue.htm Prussian Blue Pigment - The Accidental Creation of Prussian Blue ] ] by the chemist and paint maker
Heinrich Diesbachand the alchemist Johann Konrad Dippelin Berlinin 1704–05, which is why it has the alternative name of "Berlin blue". Diesbach and Dipple were attempting to create a red lake pigmentbut obtained the blue instead as a result of the potashthey were using having come from a contaminated source. [http://www.miniatures.de/int/preussisch-blau.html Military Miniatures Magazine: Parisian or Prussian Blue, Historical Paint for Miniatures]
This Prussian blue pigment is significant since it was the first stable and lightfast blue pigment to be widely used. European painters had previously used a number of pigments such as
indigo dye, smalt, and Tyrian purple, which tend to fade, and the extremely expensive ultramarineand lapis lazuli. Japanese painters and woodblock print artists likewise did not have access to a long-lasting blue pigment until they began to import Prussian blue from Europe. Cobalt bluehas been used extensively by Chinese artists in blue and white porcelains for centuries, and was introduced to Europe in the 18th century.
title= Prussian Blue
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Despite being one of the oldest known synthetic compounds, the composition of Prussian blue was uncertain until recently. The precise identification of Prussian blue was complicated by three factors: (a.) Prussian blue is extremely insoluble but also tends to form
colloids, (b.) traditional syntheses tend to afford impure compositions, and (c.) even pure Prussian blue is structurally complex, defying routine crystallographic analysis.
chemical formulaof Prussian blue is Fe7(CN)18(H2O)x where 14 ≤ x ≤ 16. The determination of the structure and the formula resulted from decades of study using IR spectroscopy, Moessbauer spectroscopy, X-ray crystallography, and neutron crystallography. Parallel studies were conducted on related materials such as Mn3 [Co(CN)6] 2 and Co3 [Co(CN)6] 2 (i.e., Co5(CN)12). Since X-ray diffractioncannot distinguish carbon from nitrogen, the location of these lighter elements is deduced by spectroscopic means as well as distances from the iron atom centers. By growing crystals slowly from 10 mol/L hydrochloric acid, Ludi obtained crystals in which the defects were ordered. These workers concluded that the framework consists of Fe(II)-CN-Fe(III) linkages, with Fe(II)-carbon distances of 1.92 Å (0.192 nanometers) and Fe(III)-nitrogen distances of 2.03 Å (0.203 nanometers). The Fe(II) centers, which are low spin, are surrounded by six carbon ligands. The Fe(III) centers, which are high spin, are surrounded on average by 4.5 nitrogen atom centers and 1.5 oxygen atom centers, the latter from water. Again, the composition is notoriously variable due to the presence of lattice defects, allowing it to be hydrated to various degrees as water molecules are incorporated into the structure to occupy four cationvacancies. The variability of Prussian blue's composition is attributable to its low solubility, which leads to its rapid precipitation vs. growth of a single phase.
The story of "Turnbull's Blue" (TB) illustrates the complications and pitfalls associated with the characterization of a composition obtained by rapid precipitation. One obtains PB by the addition of Fe(III) salts to a solution of [Fe(CN)6] 4−. TB supposedly arises by the related reaction where the valences are switched on the iron precursors, i.e. the addition of a Fe(II) salt to a solution of [Fe(CN)6] 3-. One obtains an intensely blue colored material, whose hue was claimed to differ from that of PB. It is now appreciated that TB and PB are the same because of the rapidity of electron exchange through a Fe-CN-Fe linkage. The differences in the colors for TB and PB reflect subtle differences in the method of precipitation, which strongly affects particle size and impurity content.
"Soluble" Prussian blue
PB is insoluble, but it tends to form such small crystallites that colloids are common. These colloids behave like solutions, for example they pass through fine filters. "Soluble" forms of PB tend toward compositions with the approximate formula KFe [Fe(CN)6] .
The color of Prussian blue
Prussian blue is strongly colored and tends towards black and dark purple when mixed into
oil paints. The exact hue depends on the method of preparation, which dictates the particle size. The intense blue color of Prussian blue is associated with the energy of the transfer of electrons from Fe(II) to Fe(III). Many such mixed-valence compounds absorb certain wavelenghts of visible light. In this case, orange- redlight around 680 nanometers in wavelength is absorbed, and the transmitted light appears blue as a result.
Prussian Blue has been extensively studied by
inorganic chemists and solid-state physicists because of its unusual properties.
intervalence charge transfer. Although intervalence charge transfer is well-understood today, Prussian blue was the subject of intense study when the phenomenon was discovered.
*It is electrochromic—changing from blue to colorless upon reduction. This change is caused by reduction of the Fe(III) to Fe(II) eliminating the intervalence charge transfer that causes Prussian blue's color.
*It undergoes "spin-crossover" behavior. Upon exposure to visible light the Fe(III) centers change from the low spin state to high spin states. This spin transition also changes the magnetic coupling between the iron atoms, making Prussian blue one of the few classes of materials that have a magnetic response to light. Fact|date=June 2008
Despite the presence of the
cyanideion, Prussian blue is not especially toxic because the cyanide groups are tightly bound. Other cyanometalates are similarly stable with low toxicity. Treatment with acids, however, can liberate hydrogen cyanidewhich is extremely toxic, as discussed in the article on cyanide.
Prussian blue, such as that in inks, is prepared by adding a solution containing
iron(III) chlorideto a solution of potassium ferrocyanide. During the course of the addition the solution thickens visibly and the color changes immediately to the characteristic blue of Prussian blue.
Prussian Blue in Chelation Therapy in Medicine
Prussian blue's ability to incorporate cations that have one unit of positive charge makes it useful as a chelation sequestering agent for certain heavy-metals ions. Pharmaceutical-grade Prussian blue in particular is used for patients who have ingested
thalliumor radioactive cesium. According to the International Atomic Energy Agency, an adult male can eat at least 10 grams of Prussian Blue per day without any serious harm. The U.S. Food and Drug Administration(FDA) has determined that the "500 mg Prussian blue capsules, when manufactured under the conditions of an approved New Drug Application (NDA), can be found safe and effective therapy." in certain poisoning cases. [ [http://www.FDA.gov/cder/drug/infopage/prussian_blue/Q&A.htm Questions and Answers on Prussian Blue ] ] Radiogardase (Prussian blue insoluble capsules) is a commercial product for the removal of cesium-137from the bloodstream. [ [http://www.heyltex.com/toxicology.php Heyltex Corporation - Toxicology ] ]
As a laboratory test for iron
Prussian blue is a common stain used by
pathologists to detect the presence of iron in biopsy specimens, such as in bone marrow samples.
As a pigment
Prussian blue is the coloring agent used in
engineer's blueand the pigment formed on cyanotypes - giving them their common name blueprints. Certain crayons were once colored with Prussian blue (later relabeled Midnight Blue).
Colloids derived from Prussian blue are the basis for
* Ludi, A., "Prussian Blue, an Inorganic Evergreen", Journal of Chemical Education 1981, 58, 1013.
* Sharpe, A. G., "The Chemistry of Cyano Complexes of the Transition Metals," Academic Press: London, 1976.
* Prakash R. Somani* and S. Radhakrishnan, "Electrochromic materials and devices : present and future", Materials Chemistry and Physics 77/1 (2003)117-133 (Times Cited > 125). ScienceDirect TOP 25 Hottest Articles (Jul. – Sept. 2004; Oct. – Dec. 2004; Jan. – Mar. 2005; Oct. – Dec. 2005).
* Prakash R. Somani*, A. B. Mandale, S. Radhakrishnan, "Study and development of conducting polymer based electrochromic display devices", Acta Materilia 48/11 (2000) 2859 – 2871 (Times Cited > 51).
* Prakash R. Somani and S. Radhakrishnan, "Electrochromic response in polypyrrole sensitized with Prussian Blue" Chemical Physics Letters, 292 (1998) 218 - 222 (Times Cited > 21).
* Prakash R. Somani*, D. P. Amalnerkar, S. Radhakrishnan, "Effect of moisture (in solid polymer electrolyte) on the photosensitivity of conducting polypyrrole sensitized by Prussian Blue in solid state photocells", Synthetic Metals, 110(2000) 181 – 187(Times Cited = 18).
* Prakash R. Somani* and S. Radhakrishnan, "Effect of dye aggregation on the photosensitivity of conducting polypyrrole sensitized with Prussian Blue in solid state electrochemical cells", Materials Chemistry and Physics 70/2 (2001) 150 – 155(Times Cited =13).
* Prakash R. Somani* and S. Radhakrishnan, "Charge transport processes in conducting polypyrrole / Prussian Blue bilayers", Materials Chemistry and Physics 76/1 (2002) 15 – 19 (Times Cited = 9).
* [http://www.fda.gov/cder/drug/infopage/prussian_blue/Q&A.htm The FDA's page on prussian blue]
* [http://www.bt.cdc.gov/radiation/prussianblue.asp The CDC's page on prussian blue]
* [http://www.npi.gov.au/database/substance-info/profiles/29.html National Pollutant Inventory - Cyanide compounds fact sheet]
* [http://www.heyltex.com/ Heyltex Corporation distributors of Radiogardase (Prussian blue insoluble capsules)]
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