 | |
| Names | |
|---|---|
| IUPAC name Iron(II,III) hexacyanidoferrate(II,III) | |
Other names
| |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
|
| ECHA InfoCard | 100.034.418 |
| EC Number |
|
| 1093743 | |
| UNII | |
| |
| |
| Properties | |
| C18Fe7N18 | |
| Molar mass | 859.239 g·mol−1 |
| Appearance | Blue opaque crystals |
| Insoluble | |
| Structure | |
| Face-centered cubic,cF43 | |
| Fm3m, No. 225[1] | |
| Pharmacology | |
| V03AB31 (WHO) | |
| Oral | |
| Hazards | |
| Safety data sheet (SDS) | MSDS Prussian blue |
| Related compounds | |
Othercations | Potassium ferrocyanide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Prussian blue (also known asBerlin blue,Brandenburg blue,Parisian andParis blue) is a darkbluepigment produced by oxidation of ferrousferrocyanide salts. It has thechemical formulaFe4[Fe(CN)6]3. It consists ofFe3+cations, where iron is in theoxidation state of +3, and[Fe(CN)6]4−anions, where iron is in the oxidation state of +2, so, the other name of this salt is iron(III) hexacyanoferrate(II).Turnbull's blue is essentially identical chemically, excepting that it has different impurities and particle sizes—because it is made from differentreagents—and thus it has a slightly different color.
Prussian blue was created in the early 18th century and is the first modernsynthetic pigment. It is prepared as a very finecolloidal dispersion, because the compound is not soluble in water. It contains variable amounts[2] of other ions and its appearance depends sensitively on the size of the colloidal particles. The pigment is used inpaints, it became prominent in 19th-centuryaizuri-e (藍摺り絵)Japanese woodblock prints, and it is the traditional "blue" in technicalblueprints.
In medicine, orally administered Prussian blue is used as anantidote for certain kinds ofheavy metal poisoning, e.g., bythallium(I) and radioactive isotopes ofcaesium. The therapy exploits Prussian blue's ion-exchange properties and high affinity for certain "soft" metalcations. It is on theWorld Health Organization's List of Essential Medicines, the most important medications needed in a basichealth system.[3]
Prussian blue lent its name toprussic acid (hydrogen cyanide) derived from it. In German, hydrogen cyanide is calledBlausäure ('blue acid').
Prussian blue pigment is significant since it was the first stable and relativelylightfast blue pigment to be widely used since the loss of knowledge regarding the synthesis ofEgyptian blue. European painters had previously used a number of pigments such asindigo dye,smalt, andTyrian purple, and the extremely expensiveultramarine made fromlapis lazuli.Japanese painters andwoodblock print artists, likewise, did not have access to a long-lasting blue pigment until they began to import Prussian blue from Europe.[4]
Prussian blueFe7(CN)18 (also (Fe4[Fe(CN)6]3·xH2O) was probably synthesized for the first time by the paint makerJohann Jacob Diesbach in Berlin around 1706.[5][6] The pigment is believed to have been accidentally created when Diesbach usedpotash tainted withblood to create some redcochineal dye. The original dye required potash,ferric sulfate, and dried cochineal. Instead, the blood, potash, and iron sulfate reacted to create a compound known as iron ferrocyanide, which, unlike the desired red pigment, has a very distinct blue hue.[7] It was namedPreußisch blau andBerlinisch Blau in 1709 by its first trader.[8][9][10]
The pigment readily replaced the expensive lapis lazuli-derived ultramarine and was an important topic in the letters exchanged betweenJohann Leonhard Frisch and the president of thePrussian Academy of Sciences,Gottfried Wilhelm Leibniz, between 1708 and 1716.[8] 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 termedPreussisch blau; by November 1709, the German nameBerlinisch 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 paperNotitia Coerulei Berolinensis nuper inventi in 1710, as can be deduced from his letters. Diesbach had been working for Frisch since about 1701.
To date, theEntombment of Christ, dated 1709 byPieter van der Werff (Picture Gallery,Sanssouci, Potsdam) is the oldest known painting where Prussian blue was used. Around 1710, painters at thePrussian court were already using the pigment. At around the same time, Prussian blue arrived in Paris, whereAntoine Watteau and later his successorsNicolas Lancret andJean-Baptiste Pater used it in their paintings.[5][11]François Boucher used the pigment extensively for both blues and greens.[12]
In 1731,Georg Ernst Stahl published an account of the first synthesis of Prussian blue.[13] The story involves not only Diesbach, but alsoJohann Konrad Dippel. Diesbach was attempting to create a redlake 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 hisanimal 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 John Woodward.[14][15][16]
In 1752, French chemistPierre J. Macquer made the important step of showing Prussian blue could be reduced to a salt of iron and a new acid, which could be used to reconstitute the dye.[17] The new acid,hydrogen cyanide, first isolated from Prussian blue in pure form and characterized in 1782 by Swedish chemistCarl Wilhelm Scheele,[18] was eventually given the nameBlausäure (literally "blue acid") because of its derivation from Prussian blue, and in English became known popularly as prussic acid.Cyanide, a colorless anion that forms in the process of making Prussian blue, derives its name from the Greek word for dark blue.
In the late 1800s,RabbiGershon Henoch Leiner, theHasidicRebbe ofRadzin,dyedtzitziyot with Prussian blue made withsepia, believing that this was the truetecheiles dye. Even though some have questioned its identity as techeiles because of its artificial production, and claimed that had Rabbi Leiner been aware of this he would have retracted his position that his dye was techeiles,[19] others have disputed this and claimed that Rabbi Leiner would not have retracted.[20]
From the beginning of the 18th century, Prussian blue was the predominant uniform coat color worn by the infantry and artillery regiments of thePrussian Army.[21] AsDunkelblau (dark blue), this shade achieved a symbolic importance and continued to be worn by most German soldiers forceremonial and off-duty occasions until the outbreak ofWorld War I, when it was superseded by greenish-gray field gray (Feldgrau).[22]
Prussian blue is produced by oxidation of ferrous ferrocyanide salts. These white solids have the formulaM
2Fe[Fe(CN)
6] whereM+
=Na+
orK+
. The iron in this material is all ferrous, hence the absence of deep color associated with the mixed valency. Oxidation of this white solid with hydrogen peroxide or sodium chlorate produces ferricyanide and affords Prussian blue.[23]
A "soluble" form,KFe3+[Fe2+(CN)6], which is reallycolloidal, can be made frompotassium ferrocyanide and iron(III):
The similar reaction ofpotassium ferricyanide and iron(II) results in the same colloidal solution, because[Fe3+(CN)6]3− is converted into ferrocyanide.
The "insoluble" Prussian blue is obtained if, in the reactions above, an excess of Fe(III) is added:
Despite the fact that it is prepared from cyanide salts, Prussian blue is not toxic because the cyanide groups are tightly bound to iron.[25] Both ferrocyanide ((Fe2+(CN)6)4−) and ferricyanide ((Fe3+(CN)6)3−) are particularly stable and non-toxic polymericcyanometalates due to the strong iron coordination to cyanide ions. Although cyanide bonds well with transition metals in general like chromium, these non-iron coordination compounds are not as stable as iron cyanides, therefore increasing the risk of releasing CN− ions, and subsequently comparative toxicity.[26]
In former times, the addition of iron(II) salts to a solution offerricyanide was thought to afford a material different from Prussian blue. The product was traditionally named Turnbull's blue (TB).X-ray diffraction andelectron diffraction methods have shown, though, that the structures of PB and TB are identical.[27][28] The differences in the colors for TB and PB reflect subtle differences in the methods of precipitation, which strongly affect particle size and impurity content.
Prussian white, also known asBerlin white orEverett's salt, is thesodiumend-member of the totallyreduced form of the Prussian blue in which all iron is present as Fe(II). It is a sodiumhexacyanoferrate of Fe(II) of formulaNa2Fe[Fe(CN)6].[29] Itsmolecular weight value is314 g/mol.[29]
A more generic formula allowing for the substitution ofNa+ cations byK+ cations isA(2−x)BxFe2(CN)6 (in which A or B =Na+ orK+).
The Prussian white is closely related to the Prussian blue, but it significantly differs by its crystallographic structure, molecular framework pore size, and its color. The cubic sodium Prussian white,Na(2−x)KxFe2(CN)6·yH2O, and potassium Prussian white,K(2−x)NaxFe2(CN)6·yH2O, are candidates ascathode materials forNa-ion batteries.[30] The insertion ofNa+ andK+ cations in the framework of potassium Prussian white provides favorable synergistic effects improving the long-term battery stability and increasing the number of possible recharge cycles, lengthening its service life.[30] The large-size framework of Prussian white easily accommodatingNa+ andK+ cations facilitates their intercalation and subsequent extraction during the charge/discharge cycles. The spacious and rigid host crystal structure contributes to its volumetric stability against the internal swellingstress andstrain developing in sodium-batteries after many cycles.[29] The material also offers perspectives of highenergy densities (Ah/kg) while providing high recharge rate, even at low temperature.[29]
Prussian blue is amicrocrystalline blue powder. It is insoluble, but thecrystallites tend to form a colloid. Such colloids can pass through fine filters.[2] Despite being one of the oldest known synthetic compounds, the composition of Prussian blue remained uncertain for many years. Its precise identification was complicated by three factors:
Thechemical formula of insoluble Prussian blue isFe7(CN)18·xH2O, wherex = 14–16. The structure was determined by usingIR spectroscopy,Mössbauer spectroscopy,X-ray crystallography, andneutron crystallography. Since X-ray diffraction cannot easily distinguish carbon from nitrogen in the presence of heavier elements such as iron, the location of these lighter elements is deduced by spectroscopic means, as well as by observing the distances from the iron atom centers.Neutron diffraction can easily distinguish N and C atoms, and it has been used to determine the detailed structure of Prussian blue and its analogs.[31][32][33][34][35][36][37][38][39][40][41]
PB has aface centered cubic lattice structure, with four iron(III) ions per unit cell. "Soluble" PB crystals contain interstitialK+ ions; insoluble PB has interstitial water, instead. In ideal insoluble PB crystals, the cubic framework is built from Fe(II)–C–N–Fe(III) sequences, with Fe(II)–carbon distances of 1.92Å and Fe(III)–nitrogen distances of 2.03 Å. One-fourth of the sites ofFe(CN)6 subunits (supposedly at random) are vacant (empty), leaving three such groups on average per unit cell.[42] The empty nitrogen sites are filled with water molecules instead, which are coordinated to Fe(III).
The Fe(II) centers, which arelow spin, are surrounded by six carbonligands in anoctahedral configuration. The Fe(III) centers, which arehigh spin, are octahedrally surrounded on average by 4.5 nitrogen atoms and 1.5 oxygen atoms (the oxygen from the six coordinated water molecules). Around eight (interstitial) water molecules are present in the unit cell, either as isolated molecules orhydrogen bonded to the coordinated water. It is worth noting that in solublehexacyanoferrates Fe(II or III) is always coordinated to the carbon atom of acyanide, whereas in crystalline Prussian blue Fe ions are coordinated to both C and N.[43]
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 occupycation vacancies. The variability of Prussian blue's composition is attributable to its lowsolubility, which leads to its rapidprecipitation without the time to achieve full equilibrium between solid and liquid.[42][44]
Prussian blue is strongly colored and tends towards black and dark blue when mixed intooil 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 ofelectrons from Fe(II) to Fe(III).[45] Many suchmixed-valence compounds absorb certain wavelengths of visible light resulting fromintervalence charge transfer. In this case, red light around 680nanometers in wavelength is absorbed, and the reflected light appears blue as a result.[46]
Like most high-chromapigments, Prussian blue cannot be accurately displayed on a computer display. Prussian blue iselectrochromic—changing from blue to colorless uponreduction. This change is caused by reduction of the Fe(III) to Fe(II), eliminating theintervalence charge transfer that causes Prussian blue's color.
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Because it is easily made, cheap, nontoxic, and intensely colored, Prussian blue has attracted many applications. It was adopted as a pigment very soon after its invention and was almost immediately widely used in oil paints, watercolor, and dyeing.[48] The dominant uses are for pigments: about 12,000tonnes of Prussian blue are produced annually for use in black and bluishinks. A variety of other pigments also contain the material.[23]Engineer's blue and the pigment formed oncyanotypes—giving them their common nameblueprints. Certaincrayons were once colored with Prussian blue (later relabeledmidnight blue). Similarly, Prussian blue is the basis forlaundry bluing.
Nanoparticles of Prussian blue are used as pigments in some cosmetics ingredients, according to the European Union Observatory for Nanomaterials.
| Prussian blue | |
|---|---|
 Color coordinates | |
| Hex triplet | #003153 |
| sRGBB (r,g,b) | (0, 49, 83) |
| HSV (h,s,v) | (205°, 100%, 33%) |
| CIELChuv (L,C,h) | (19, 30, 247°) |
| Source | swiss.csail.mit.edu[49] |
| B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred) | |
Prussian blue's ability to incorporatemonovalent metalliccations (Me+) makes it useful as asequestering agent for certaintoxic heavy metals. Pharmaceutical-grade Prussian blue in particular is used for people who have ingestedthallium (Tl+) orradioactivecaesium (134Cs+,137Cs+). According to theInternational Atomic Energy Agency (IAEA), an adult male can eat at least 10 g of Prussian blue per day without serious harm. TheU.S. Food and Drug Administration (FDA) has determined the "500-mg Prussian blue capsules, when manufactured under the conditions of an approved New Drug Application, can be found safe and effective therapy" in certain poisoning cases.[50][51] Radiogardase (Prussian blue insoluble capsules[52]) is a commercial product for the removal ofcaesium-137 from theintestine, so indirectly from thebloodstream by intervening in theenterohepatic circulation of caesium-137,[53] reducing the internal residency time (and exposure) by about two-thirds. In particular, it was used toadsorb and remove137Cs+ from those poisoned in theGoiânia accident in Brazil.[2]
Prussian blue is a commonhistopathology stain used bypathologists to detect the presence of iron inbiopsy specimens, such as inbone marrow samples. The original stain formula, known historically (1867) as "Perls Prussian blue" after its inventor, German pathologistMax Perls (1843–1881), used separate solutions ofpotassium ferrocyanide and acid to staintissue (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.[54]
Engineer's blue, Prussian blue in an oily base, is the traditional material used for spotting metal surfaces such assurface plates andbearings forhand scraping. A thin layer of nondrying 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 marked high spots. Prussian blue is preferable because it will not abrade the extremely precise reference surfaces as many ground pigments may. Other uses include marking gear teeth during assembly to determine their interface characteristics.
Prussian blue is also used in a drying form to lay out features for parts on raw stock. The machinist will apply the prussian blue and then scribe the features to be machined using tools like calipers and height gauges. Prussian blue is valued in this application because the scribed lines in the coating allow the machinist to accurately feel for features with marking tools like prick punches.
Prussian blue is formed in the Prussian blue assay for totalphenols. 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 orpolyphenols.[55][56]
Prussian blue is present in some preparations oflaundry bluing, such asMrs. Stewart's Bluing.[57]
Prussian blue (PB) has been studied for its applications in electrochemical energy storage since 1978.[58] Prussian blue proper (the Fe-Fe solid) shows two well-defined reversible redox transitions in K+ solutions. Weakly solvated potassium ions (as well as Rb+ and Cs+, not shown) have thesolvated radius, which fits the framework of Prussian Blue. On the other hand, the sizes of solvated Na+ and Li+ are too large for the PB cavity, and the intercalation of these ions is hindered and much slower. The low and high voltage sets of peaks in the cyclic voltammetry correspond to 1 and2/3 electron per Fe atom, respectively.[59] The high voltage set is due to theFe3+/Fe2+ transition at the low-spin Fe ions coordinated to C-atoms. The low-voltage set is due to high-spin Fe ion coordinated to N-atoms.[60][61][62]
It is possible to replace the Fe metal centers in PB with other metal ions such as Mn, Co, Ni, Zn, to form electrochemically active Prussian blue analogues (PBAs). PB/PBAs and their derivatives have also been evaluated as electrode materials for reversible alkali-ion insertion and extraction inlithium-ion battery,sodium-ion battery, andpotassium-ion battery.[citation needed]
"Wear Your Love Like Heaven" is a song and US single by British singer-songwriter Donovan, released in 1967. First line "Color in sky, Prussian blue".
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