View source for Prussian blue

{{for|the musical duo|Prussian Blue}}

{{Chembox
| Watchedfields = changed
|  verifiedrevid = 268882775
|  ImageFile = Prussian blue.jpg|
|  ImageSize = 250px
|  ImageName = Sample of prussian blue 
|  PIN = Iron(II,III) hexacyanoferrate(II,III)
|  SystematicName = tetrairon(3+) tris(hexacyanoirontetrauide)
|  OtherNames = Berlin blue<br />
Ferric ferrocyanide<br />
Ferric hexacyanoferrate<br />
Iron(III) ferrocyanide<br />
Iron(III) hexacyanoferrate(II)<br />
Parisian blue
| Section1 = {{Chembox Identifiers
|  CASNo = 14038-43-8
|   CASNo_Ref = {{cascite}}
|  PubChem = 2724251
|   PubChem_Ref = {{Pubchemcite}}
|  ChemSpiderID = 20074656
|   ChemSpiderID_Ref = {{Chemspidercite}}
|  EINECS = 237-875-5
|  ChEBI = 30069
|  RTECS = V03AB31
|  SMILES = [Fe+3].[Fe+3].[Fe+3].[Fe+3].<br />
N#C[Fe-4](C#N)(C#N)(C#N)(C#N)<br />
C#N.N#C[Fe-4](C#N)(C#N)(C#N)<br />
(C#N)C#N.N#C[Fe-4](C#N)(C#N)<br />
(C#N)(C#N)C#N
|  InChI = 1S/18CN.7Fe/c18*1-2;;;;;;;/q;;;;;;;;;;;;;;;;;;3*-4;4*+3
|  InChIKey = DNMNDNSFJMUUFM-UHFFFAOYSA-N
|  Gmelin = 1093743}}
| Section2 = {{Chembox Properties
| Formula = K[Fe<sup>III</sup>Fe<sup>II</sup>(CN)<sub>6</sub>]&nbsp; or<br />
Fe<sup>III</sup><sub>4</sub>[Fe<sup>II</sup>(CN)<sub>6</sub>]<sub>3</sub>.xH<sub>2</sub>O 
| MolarMass = 859.23 g/mol
| Appearance = blue [[microcrystalline]] powder
| Density = 
| Solubility = insoluble
| MeltingPt = 
| BoilingPt = 
}}
| Section3 = {{Chembox Structure
| Coordination = 
| CrystalStruct = 
}}
| Section5 = {{Chembox Pharmacology
|  AdminRoutes = Oral
|  Bioavail = 
|  Metabolism = 
|  HalfLife = 
|  ProteinBound =
|  Excretion = 
|  Legal_status = 
|  Legal_US = 
|  Legal_UK = 
|  Legal_AU = 
|  Legal_CA = 
|  PregCat = 
|  PregCat_AU = 
|  PregCat_US = }}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [https://fscimage.fishersci.com/msds/62402.htm MSDS prussian blue]
| EUIndex = Not listed
| MainHazards = 
| RPhrases = 
| SPhrases = 
| FlashPt = Non-flammable
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Sodium ferrocyanide]]<br/>[[Potassium ferrocyanide]]<br/>[[Potassium ferricyanide]]
}}
}}
{{infobox color|textcolor=white|
 title= Prussian Blue|
 hex= 003153|
 r=0|g=49|b= 83|
 c=63|m= 35|y= 14|k=72|
 h= 205|s=100|v=43
}}

'''Prussian blue''' is a dark blue [[pigment]] with the idealized [[chemical formula|formula]] Fe<sub>7</sub>(CN)<sub>18</sub>⋅14H<sub>2</sub>O.<ref name='Herren'/>
Another name for the color ''Prussian blue'' is ''Berlin blue'' or, in [[painting]], ''Parisian blue''. '''Turnbull's blue''' is the same substance but is made from different [[reagent]]s.

Prussian blue is one of the first synthetic pigments. The pigment is famously complex, owing to the presence of variable amounts of other ions and the sensitive dependence of its appearance to the size of the particles. The pigment is used in [[paint]]s, and it is the traditional "blue" in [[blueprint]]s. It has been used as an [[antidote]] for certain kinds of [[heavy metal poisoning]]. 

==History==
Prussian blue was probably synthesized for the first time by the paint maker Diesbach in Berlin around the year 1706.<ref name=Bartoll>{{cite journal| url =http://www.ndt.net/article/art2008/papers/029bartoll.pdf| title =The early use of prussian blue in paintings| format= PDF| author = Jens Bartoll| journal = 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008| accessdate = 2010-01-22}}</ref> Most historical sources do not mention a first name of Diesbach. Only Berger refers to him as Johann Jacob Diesbach.<ref>J. E. Berger: ''Kerrn aller Fridrichs=Städtschen Begebenheiten'' Manuskript, Berlin, ca.1730 (Berlin, Staatsbibliothek zu Berlin – Preußischer Kulturbesitz, Handschriftenabteilung, Ms. Boruss. quart. 124)</ref> It was named "Preußisch blau" and "Berlinisch Blau" in 1709 by its first trader.<ref name=Frisch>J. L. Frisch: ''Briefwechsel mit Gottfried Wilhelm Leibniz'' L. H. Fischer (ed.), Berlin, Stankiewicz Buchdruck, 1896, reprint Hildesheim/New York: Georg Olms Verlag, 1976</ref> The pigment was an important topic in the letters exchanged between [[Johann Leonhard Frisch]] and the president of the Royal Academy of Sciences, [[Gottfried Wilhelm Leibniz]], between 1708 and 1716.<ref name=Frisch/> It is first mentioned in a letter written by Frisch to Leibniz, from March 31, 1708. Not later than 1708, Frisch began to promote and sell the pigment across Europe. By August 1709, the pigment had been termed "Preussisch blau"; by November 1709, the German name "Berlinisch Blau" had been used for the first time by Frisch. Frisch himself is the author of the first known publication of Prussian blue in the paper ''Notitia Coerulei Berolinensis nuper inventi'' in 1710, as can be deduced from his letters. Diesbach had been working for Frisch since about 1701.

In 1731, [[Georg Ernst Stahl]] published a story dealing with the incidence of the first synthesis of Prussian blue.<ref>G. E. Stahl: ''Experimenta, Observationes, Animadversiones'' CCC Numero, Chymicae et Physicae, Berlin, 1731</ref> The story involves not only Diesbach but also [[Johann Konrad Dippel]]. Diesbach was attempting to create a red [[lake pigment]] from [[cochineal]] but obtained the blue instead as a result of the contaminated [[potash]] he was using. He borrowed the potash from Dippel, who had used it to produce his "animal oil". No other known historical source mentions Dippel in this context. It is therefore difficult to judge the reliability of this story today. In 1724, the recipe was finally published by Woodward.<ref>J. Woodward: ''Praeparatio coerulei Prussiaci es Germanica missa'' in: ''Philosophical Transactions'', London, 33, 1726</ref>

To date, the "Entombment of Christ", dated 1709 by [[Pieter van der Werff]] (Picture Gallery, [[Sanssouci]], Potsdam) is the oldest known painting where Prussian blue was used. Around 1710, painters at the Prussian court were already using the pigment. At around the same time, Prussian blue arrived in Paris, where [[Antoine Watteau]] and later his successors [[Nicolas Lancret]] and [[Jean-Baptiste Pater]] used it in their paintings.<ref>J.Bartoll, B. Jackisch, M. Most, E. Wenders de Calisse, C. M. Vogtherr: ''Early Prussian Blue. Blue and green pigments in the paintings by Watteau, Lancret and Pater in the collection of Frederick II of Prussia'' In: ''TECHNE'' 25, 2007, S. 39-46</ref>

[[File:The Great Wave off Kanagawa.jpg|right|thumb|250px|"[[The Great Wave off Kanagawa]]" by [[Hokusai]], a famous artwork which makes extensive use of Prussian blue.]]
This Prussian blue pigment is significant since it was the first stable and relatively lightfast blue pigment to be widely used following the loss of knowledge regarding the synthesis of [[Egyptian Blue]]. 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 [[ultramarine]] made from [[lapis lazuli]]. [[Japanese painting|Japanese painters]] and [[Woodblock printing in Japan|woodblock print artists]] likewise did not have access to a long-lasting blue pigment until they began to import Prussian blue from Europe. [[Cobalt blue]] has been used extensively by Chinese artists in [[Chinese porcelain#Blue and white wares|blue and white porcelains]] for centuries, and was introduced to Europe in the 18th century.

In 1752 the French chemist [[Pierre J. Macquer]] made the important step of showing the Prussian blue could be reduced to a salt of iron, and a new acid, which could be used to reconstitute the dye. The new acid, [[hydrogen cyanide]], first isolated from Prussian blue in pure form and characterized about 1783 by the Swedish chemist [[Carl Wilhelm Scheele]], was eventually given the name ''Blausäure'' (literally "Blue acid") because of its derivation from Prussian blue, and in English became known popularly as ''Prussic acid.'' Prussian blue would also give the name to the [[cyanide]] family of compounds, which are named from the Greek word for "blue," because they were first isolated from Prussian blue.

==Production==
Prussian blue has a "soluble" form, K[Fe<sup>III</sup>Fe<sup>II</sup>(CN)<sub>6</sub>], and an "insoluble" form, Fe<sup>III</sup><sub>4</sub>[Fe<sup>II</sup>(CN)<sub>6</sub>]<sub>3</sub>.xH<sub>2</sub>O.

* Soluble Prussian blue can be made from [[potassium ferrocyanide]] and iron(III):
:K<sup>+</sup> + Fe<sup>3+</sup> + [Fe<sup>II</sup>(CN)<sub>6</sub>]<sup>4-</sup> → KFe<sup>III</sup>[Fe<sup>II</sup>(CN)<sub>6</sub>] 
The similar reaction of [[potassium ferricyanide]] and iron(II) results in the same [[colloid]]al solution, because [Fe<sup>III</sup>(CN)<sub>6</sub>]<sup>3-</sup> is converted into ferrocyanide, as the following equilibrium lies on the right-hand side:
:<math>\mathrm{Fe^{2+} + [Fe(CN)_6]^{3-} \ \rightleftharpoons \ Fe^{3+} + [Fe(CN)_6]^{4-}}</math>

* Insoluble Prussian blue is produced if in the reactions above an excess of Fe<sup>3+</sup> or Fe<sup>2+</sup>, respectively, is added.&nbsp; In the first case:
:4Fe<sup>3+</sup> + 3[Fe<sup>II</sup>(CN)<sub>6</sub>]<sup>4-</sup> → Fe<sup>III</sup>[Fe<sup>III</sup>Fe<sup>II</sup>(CN)<sub>6</sub>]<sub>3</sub>&nbsp; <ref>Egon Wiberg,Nils Wiberg,Arnold Frederick Holleman: [http://books.google.com/books?id=vEwj1WZKThEC&pg=PA1444 Inorganic chemistry], p.1444. Academic Press, 2001; Google books</ref><br />

Soluble Prussian blue for use in inks is prepared by adding a solution containing [[iron(III) chloride]] to 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.

===Turnbull's blue===
[[File:HexacyanidoferratIII 2.svg|thumb|180px|[[Ferricyanide]] ion, used to make 'Turnbull's blue']]
Whereas "Prussian blue" (PB) can be obtained by two different methods, either by addition of a Fe(III) salt to a solution of [[ferrocyanide]] or by addition of a Fe(II) salt to a solution of [[ferricyanide]], in former times the methods were thought to produce two different products.

The product of Fe(II) and [Fe(CN)<sub>6</sub>]<sup>3-</sup> was traditionally named "Turnbull's Blue" (TB). It has been shown, however, by means of [[X-ray diffraction]] and [[electron diffraction]] methods, that the structures of PB and TB are identical.<ref>Toru Ozeki, Koichi Matsumoto, Seiichiro Hikime: [http://pubs.acs.org/doi/abs/10.1021/ac00278a041 ''Photoacoustic spectra of prussian blue and photochemical reaction of ferric ferricyanide''] Anal. Chem., 1984, 56 (14), pp. 2819–2822. {{doi|10.1021/ac00278a041}}</ref><ref>Izatt, et al. [http://pubs.acs.org/doi/abs/10.1021/ic50091a012 ''Calorimetric study of Prussian blue and Turnbull's blue formation''] Inorg. Chem., 1970, 9 (9), pp. 2019–2021. {{doi|10.1021/ic50091a012}}</ref> 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.

== Properties ==

Prussian blue is a [[microcrystalline]] blue powder. It is insoluble, but the [[crystallite]]s tend to form a [[colloid]]. Such colloids can pass through fine filters<ref name=Dunbar>*Dunbar, K. R. and Heintz, R. A., "Chemistry of Transition Metal Cyanide Compounds: Modern Perspectives", Progress in Inorganic Chemistry, 1997, 45, 283-391.</ref>. Despite being one of the oldest known synthetic compounds, the composition of Prussian blue remained uncertain for many years. The precise identification of Prussian blue was complicated by three factors:
# Prussian blue is extremely insoluble but also tends to form colloids;
# Traditional syntheses tend to afford impure compositions;
# Even pure Prussian blue is structurally complex, defying routine crystallographic analysis.

===Crystal structure===
The [[chemical formula]] of insoluble Prussian blue is Fe<sub>7</sub>(CN)<sub>18</sub>.xH<sub>2</sub>O, where x = 14-16. The structure was determined by using [[IR spectroscopy]], [[Moessbauer spectroscopy]], [[X-ray crystallography]], and [[neutron crystallography]]. Since [[X-ray diffraction]] cannot distinguish carbon from nitrogen, the location of these lighter elements is deduced by spectroscopic means as well as by observing the distances from the iron atom centers.

PB has a [[Cubic crystal system|cubic lattice structure]]. Soluble PB crystals contain interstitial K<sup>+</sup> ions; insoluble PB has interstitial water instead.<br />
In ideal insoluble PB crystals, the cubic framework is built from Fe(II)-C-N-Fe(III) sequences, with Fe(II)-carbon distances of 1.92 Å (0.192 nanometers) and Fe(III)-nitrogen distances of 2.03 Å (0.203 nanometers). One-fourth of the sites of Fe(CN)<sub>6</sub> subunits are vacant (empty), leaving three such groups. The empty nitrogen sites are filled with water molecules instead, which are coordinated to Fe(III).

The Fe(II) centers, which are [[low spin]], are surrounded by six carbon [[ligand]]s in an [[octahedral]] configuration. The Fe(III) centers, which are [[high spin]], are octahedrally surrounded on average by 4.5 nitrogen atoms and 1.5 oxygen atoms (the oxygen from the six coordinated water molecules). Additional eight (interstitial) water molecules are present in the unit cell, either as isolated molecules or [[hydrogen bond|hydrogen bonded]] to the coordinated water.

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 [[cation]] vacancies. The variability of Prussian blue's composition is attributable to its low [[solubility]], which leads to its rapid [[precipitation (chemistry)|precipitation]] without the time to achieve full equilibrium between solid and liquid.
<ref name='Herren'>F. Herren, P. Fischer, A. Ludi, W. Haelg [http://pubs.acs.org/doi/abs/10.1021/ic50206a032 "Neutron diffraction study of Prussian Blue, Fe4[Fe(CN)6]3.xH2O. Location of water molecules and long-range magnetic order"] Inorg. Chem., 1980, 19 (4), pp 956–959.{{DOI|10.1021/ic50206a032}}</ref>
<ref name='Lundgren'>C. A. Lundgren, Royce W. Murray: [http://pubs.acs.org/doi/abs/10.1021/ic00278a036 ''Observations on the composition of Prussian blue films and their electrochemistry''] Inorg. Chem., 1988, 27 (5), pp 933–939; {{doi|10.1021/ic00278a036}}</ref>

===Color===
Prussian blue is strongly colored and tends towards black and dark purple when mixed into [[oil paint]]s. 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 [[electron]]s from Fe(II) to Fe(III). Many such [[mixed-valence compound]]s absorb certain wavelengths of visible light resulting from [[intervalence charge transfer]]. In this case, [[Orange (colour)|orange]]-[[red]] light around 680 [[nanometer]]s in wavelength is absorbed, and the transmitted light appears blue as a result.

PB is [[electrochromism|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.

===Other properties===
*Despite the presence of the [[cyanide]] ion, Prussian blue is not especially toxic because the cyanide groups are tightly bound to Fe. Other cyanometalates are similarly stable with low toxicity. Treatment with acids, however, can liberate the extremely toxic [[hydrogen cyanide]].

==Uses==

===Prussian blue in medicine===
Prussian blue's ability to incorporate monocations makes it useful as a sequestering agent for certain heavy metal poisons. Pharmaceutical-grade Prussian blue in particular is used for patients who have ingested [[thallium]] or [[radioactive decay|radioactive]] [[caesium]]. According to the [[International Atomic Energy Agency]], an adult male can eat at least 10 grams of Prussian blue per day without 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.<ref>{{cite web| url =http://www.fda.gov/Drugs/EmergencyPreparedness/BioterrorismandDrugPreparedness/ucm130337.htm| title = Questions and Answers on Prussian Blue| accessdate = 2009-06-06}}</ref> Radiogardase (Prussian blue insoluble capsules <ref>Radiogardase: [http://www.heyltex.com/radiogardasePackageInsert.php ''Package insert with formula'']</ref>) is a commercial product for the removal of [[caesium-137]] from the bloodstream.<ref>[http://www.heyltex.com/toxicology.php Heyltex Corporation - Toxicology]</ref>

===As a laboratory histopathology stain for iron===
[[File:Intra-alveolar hemosiderin deposition - Prussian blue stain.jpg|thumb|Prussian blue stain]]
Prussian blue is a common [[histopathology]] stain used by [[pathologist]]s to detect the presence of iron in biopsy specimens, such as in bone marrow samples. The original stain formula, known historically (1867) as "[[Perls' Prussian blue]]" after its inventor, German pathologist Max Perls (1843-1881), used separate solutions of potassium ferrocyanide and acid to stain tissue (these are now used combined, just before staining). Iron deposits in tissue then form the purple Prussian blue dye in place, and are visualized as blue or purple deposits.<ref>[http://www.scribd.com/doc/4448747/Perl Formula for Perls' Prussian blue stain]. Accessed April 2, 2009.</ref> The formula is also known as Perls Prussian blue and (incorrectly) as '''Perl's''' Prussian blue.

===As a pigment===
Prussian blue is the coloring agent used in [[engineer's blue]] and the pigment formed on [[cyanotype]]s - giving them their common name [[blueprint]]s. Certain [[crayon]]s were once colored with Prussian blue (later relabeled [[Midnight blue#Dark midnight blue|Midnight Blue]]). It is also a popular pigment in paints.  Similarly, Prussian blue is the basis for [[laundry bluing]].

===By machinists and toolmakers===
Prussian blue in oil paint is the traditional material used for spotting metal surfaces such as surface plates and bearings for hand scraping. A thin layer of non-drying paste is applied to a reference surface and transfers to the high spots of the workpiece. The toolmaker then scrapes, stones, or otherwise removes the high spots. Prussian blue is preferable because it will not abrade the extremely precise reference surfaces as many ground pigments may.

===Analytical chemistry===
Prussian blue is formed in the Prussian blue assay for total phenols.  Samples and phenolic standards are given acidic ferric chloride and ferricyanide which is reduced to ferrocyanide by the phenols.  The ferric chloride and ferrocyanide react to form Prussian blue.  Comparing the absorbance at 700 nm of the samples to the standards allows for the determination of total phenols.<ref>{{PDFlink|[http://www.users.muohio.edu/hagermae/tannin.pdf Tannin Chemistry]|1.41&nbsp;MB}}Accessed December 19, 2009</ref>

==See also==
{{colbegin|3}}
*[[Potassium ferrocyanide]]
*[[Potassium ferricyanide]]
*[[Methyl blue]]
*[[Methylene blue]]
*[[New methylene blue]]
*[[Egyptian Blue]]
*[[Han Purple]]
*[[Gentian violet]]
*[[Fluorescein]]
{{colend}}

==External links==
*[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)]
*[http://www.gutenberg-e.org/lowengard/C_Chap32.html Sarah Lowengard, "Prussian Blue" in ''The Creation of Color in Eighteenth Century Europe'' Columbia University Press, 2006]

==References==
{{Reflist|2}}

{{Shades of blue}}
{{Antidotes}}
{{Stains}}

[[Category:Cyanides]]
[[Category:Iron compounds]]
[[Category:Inorganic pigments]]
[[Category:Coordination compounds]]
[[Category:Mixed valence compounds]]
[[Category:Shades of blue]]
[[Category:Photographic chemicals]]
[[Category:World Health Organization essential medicines]]

{{Link GA|es}}

[[ca:Blau de Prússia]]
[[de:Berliner Blau]]
[[es:Azul de Prusia]]
[[fr:Bleu de Prusse]]
[[ko:프러시안 블루]]
[[it:Blu di Prussia]]
[[he:כחול פרוסי]]
[[la:Caeruleus Berolinus]]
[[lt:Karaliaučiaus mėlis]]
[[nl:Pruisisch blauw]]
[[ja:紺青]]
[[no:Preussisk blå]]
[[pl:Błękit pruski (pigment)]]
[[pt:Azul da prússia]]
[[ro:Albastru de Berlin]]
[[ru:Берлинская лазурь]]
[[simple:Prussian blue]]
[[fi:Preussinsininen]]
[[sv:Berlinerblått]]
[[zh-yue:洋靛]]
[[zh:普鲁士蓝]]
[[Category:2Fix]]