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'''Praseodymium''' is a [[Chemistry:Chemical element|chemical element]]; it has [[Chemistry:Symbol|symbol]] '''Pr''' and the [[Physics:Atomic number|atomic number]] 59. It is the third member of the [[Chemistry:Lanthanide|lanthanide]] series and is considered one of the rare-earth metals. It is a soft, silvery, malleable and ductile [[Chemistry:Metal|metal]], valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in [[Earth:Native element mineral|native form]], and pure praseodymium metal slowly develops a green oxide coating when exposed to air.

Praseodymium always occurs naturally together with the other rare-earth metals. It is the sixth-most abundant rare-earth element and fourth-most abundant lanthanide, making up 9.1 [[Parts per million|parts per million]] of the Earth's crust, an abundance similar to that of [[Chemistry:Boron|boron]]. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare-earth oxide residue he called [[Chemistry:Didymium|didymium]] from a residue he called "lanthana", in turn separated from [[Chemistry:Cerium|cerium]] salts. In 1885, the Austrian chemist [[Biography:Carl Auer von Welsbach|Carl Auer von Welsbach]] separated didymium into two elements that gave salts of different colours, which he named praseodymium and [[Chemistry:Neodymium|neodymium]]. The name praseodymium comes from the Ancient Greek {{lang|grc|πράσινος}} ({{transl|grc|prasinos}}), meaning '[[Biology:Leek|leek]]-green', and {{lang|grc|δίδυμος}} ({{transl|grc|didymos}}) 'twin'.

Like most [[Chemistry:Rare-earth element|rare-earth element]]s, praseodymium most readily forms the +3 [[Chemistry:Oxidation state|oxidation state]], which is the only stable state in [[Chemistry:Aqueous solution|aqueous solution]], although the +4 oxidation state is known in some solid compounds and, uniquely among the lanthanides, the +5 oxidation state is attainable in [[Physics:Matrix isolation|matrix-isolation conditions]]. The 0, +1, and +2 oxidation states are rarely found. Aqueous praseodymium ions are yellowish-green, and similarly, praseodymium results in various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its ability to filter yellow light from light sources.

==Physical properties==
Praseodymium is the third member of the [[Chemistry:Lanthanide|lanthanide]] series, and a member of the rare-earth metals. In the [[Chemistry:Periodic table|periodic table]], it appears between the lanthanides [[Chemistry:Cerium|cerium]] to its left and [[Chemistry:Neodymium|neodymium]] to its right, and above the [[Chemistry:Actinide|actinide]] [[Chemistry:Protactinium|protactinium]]. It is a ductile metal with a hardness comparable to that of [[Chemistry:Silver|silver]].<ref name="CRC">{{RubberBible86th}}</ref> Praseodymium is calculated to have a very large [[Physics:Atomic radius|atomic radius]]; with a radius of 247&nbsp;pm, [[Chemistry:Barium|barium]], [[Chemistry:Rubidium|rubidium]] and [[Chemistry:Caesium|caesium]] are larger.<ref>{{cite journal |last1=Clementi |first1=E. |last2=Raimond |first2=D. L. |last3=Reinhardt |first3=W. P. |year=1967 |title=Atomic Screening Constants from SCF Functions. II. Atoms with 37 to 86 Electrons |journal=Journal of Chemical Physics |volume=47 |issue=4 |pages=1300–1307 |bibcode=1967JChPh..47.1300C |doi=10.1063/1.1712084}}</ref> However, observationally, it is usually 185&nbsp;pm.<ref>{{cite journal |last=Slater|first=J. C. |year=1964 |title=Atomic Radii in Crystals |journal=Journal of Chemical Physics |volume=41 |issue=10 |pages=3199–3205 |bibcode=1964JChPh..41.3199S |doi=10.1063/1.1725697}}</ref> Praseodymium's 59 electrons are arranged in the [[Physics:Electron configuration|configuration]] [Xe]4f<sup>3</sup>6s<sup>2</sup>; theoretically, all five outer electrons can act as [[Physics:Valence electron|valence electron]]s, but the use of all five requires extreme conditions and normally, praseodymium only gives up three or sometimes four electrons in its compounds.<ref name="Greenwood1232">Greenwood and Earnshaw, pp. 1232–5</ref>

Like most other metals in the lanthanide series, praseodymium usually only uses three electrons as valence electrons, as afterward the remaining 4f electrons are too strongly bound: this is because the 4f orbitals penetrate the most through the inert xenon core of electrons to the nucleus, followed by 5d and 6s, and this increases with higher ionic charge. Praseodymium nevertheless can continue losing a fourth and even occasionally a fifth valence electron because it comes very early in the lanthanide series, where the nuclear charge is still low enough and the 4f subshell energy high enough to allow the removal of further valence electrons.<ref name="Greenwood1235">Greenwood and Earnshaw, pp. 1235–8</ref> Thus, similarly to the other early trivalent lanthanides, praseodymium has a [[Close-packing of equal spheres|double hexagonal close-packed]] crystal structure at room temperature. At about 560&nbsp;°C, it transitions to a face-centered cubic structure, and a body-centered cubic structure appears shortly before the melting point of 935&nbsp;°C.<ref>[http://www.osti.gov/bridge/servlets/purl/4010212-0BbwUC/4010212.pdf "Phase Diagrams of the Elements"], David A. Young, UCRL-51902 "Prepared for the U.S. Energy Research & Development Administration under contract No. W-7405-Eng-48".</ref>

Praseodymium, like all of the lanthanides, is [[Physics:Paramagnetic|paramagnetic]] at room temperature.<ref>{{cite book|last1=Cullity|first1=B. D.|last2=Graham|first2=C. D.|year=2011|title=Introduction to Magnetic Materials|publisher={{wipe|John Wiley & Sons}}|isbn=978-1-118-21149-6}}</ref> Unlike some other rare-earth metals, which show [[Physics:Antiferromagnetic|antiferromagnetic]] or [[Physics:Ferromagnetic|ferromagnetic]] ordering at low temperatures, praseodymium is paramagnetic at all temperatures above 1&nbsp;K.<ref name="jackson" />

==Chemical properties==
[[File:Praseodymium(III) hydroxide.jpg|thumb|Praseodymium(III) hydroxide]]
Praseodymium metal tarnishes slowly in air, forming a [[Physics:Spallation|spalling]] green oxide layer like [[Chemistry:Iron|iron]] rust; a centimetre-sized sample of praseodymium metal corrodes completely in about a year.<ref>{{cite web|url=http://www.elementsales.com/re_exp/index.htm |title = Rare-Earth Metal Long Term Air Exposure Test|access-date=2009-08-08}}</ref> It burns readily at 150&nbsp;°C to form [[Chemistry:Praseodymium(III,IV) oxide|praseodymium(III,IV) oxide]], a nonstoichiometric compound approximating to Pr<sub>6</sub>O<sub>11</sub>:<ref name="webelements">{{cite web| url =https://www.webelements.com/praseodymium/chemistry.html| title =Chemical reactions of Praseodymium| publisher=Webelements| access-date=9 July 2016}}</ref>
:12 Pr + 11 O<sub>2</sub> → 2 Pr<sub>6</sub>O<sub>11</sub>

This may be reduced to [[Chemistry:Praseodymium(III) oxide|praseodymium(III) oxide]] (Pr<sub>2</sub>O<sub>3</sub>) with hydrogen gas.<ref name="Greenwood1238">Greenwood and Earnshaw, pp. 1238–9</ref> [[Chemistry:Praseodymium(IV) oxide|Praseodymium(IV) oxide]], PrO<sub>2</sub>, is the most oxidised product of the combustion of praseodymium and can be obtained by either reaction of praseodymium metal with pure oxygen at 400&nbsp;°C and 282&nbsp;bar<ref name="Greenwood1238" /> or by disproportionation of Pr<sub>6</sub>O<sub>11</sub> in boiling acetic acid.<ref>{{cite journal|title= Hydrolytische spaltung von höheren oxiden des Praseodyms und des terbiums|author=Brauer, G. |author2=Pfeiffer, B. |date=1963|pages=171–176|volume=5|journal= Journal of the Less Common Metals|doi=10.1016/0022-5088(63)90010-9|issue=2}}</ref><ref>{{cite journal|title=Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO2, PrO2, and TbO2 |author1=Minasian, S.G. |author2=Batista, E.R. |author3=Booth, C.H. |author4=Clark, D.L. |author5=Keith, J.M. |author6=Kozimor, S.A. |author7=Lukens, W.W. |author8=Martin, R.L. |author9=Shuh, D.K. |author10=Stieber, C.E. |author11=Tylisczcak, T. |author12=Wen, Xiao-dong|date=2017|pages=18052–18064|volume=139|journal=Journal of the American Chemical Society|doi=10.1021/jacs.7b10361|pmid=29182343 |issue=49|osti=1485070 |s2cid=5382130 |url=https://escholarship.org/content/qt4dt0d19b/qt4dt0d19b.pdf?t=p0hj5c }}</ref> The reactivity of praseodymium conforms to [[Chemistry:Periodic trends|periodic trends]], as it is one of the first and thus one of the largest lanthanides.<ref name="Greenwood1235" /> At 1000&nbsp;°C, many praseodymium oxides with composition PrO<sub>2−''x''</sub> exist as disordered, nonstoichiometric phases with 0 < ''x'' < 0.25, but at 400–700&nbsp;°C the oxide defects are instead ordered, creating phases of the general formula Pr<sub>''n''</sub>O<sub>2''n''−2</sub> with ''n'' = 4, 7, 9, 10, 11, 12, and ∞. These phases PrO<sub>''y''</sub> are sometimes labelled α and β′ (nonstoichiometric), β (''y'' = 1.833), δ (1.818), ε (1.8), ζ (1.778), ι (1.714), θ, and σ.<ref name="Greenwood643">Greenwood and Earnshaw, pp. 643–4</ref>

Praseodymium is an electropositive element and reacts slowly with cold water and quite quickly with hot water to form praseodymium(III) hydroxide:<ref name="webelements" />
:2 Pr (s) + 6 H<sub>2</sub>O (l) → 2 Pr(OH)<sub>3</sub> (aq) + 3 H<sub>2</sub> (g)

Praseodymium metal reacts with all the stable [[Chemistry:Halogen|halogen]]s to form trihalides:<ref name="webelements" />
:2 Pr (s) + 3 F<sub>2</sub> (g) → 2 PrF<sub>3</sub> (s) [green]
:2 Pr (s) + 3 Cl<sub>2</sub> (g) → 2 PrCl<sub>3</sub> (s) [green]
:2 Pr (s) + 3 Br<sub>2</sub> (g) → 2 PrBr<sub>3</sub> (s) [green]
:2 Pr (s) + 3 I<sub>2</sub> (g) → 2 PrI<sub>3</sub> (s)
The [[Chemistry:Praseodymium(IV) fluoride|tetrafluoride, PrF<sub>4</sub>]], is also known, and is produced by reacting a mixture of [[Chemistry:Sodium fluoride|sodium fluoride]] and [[Chemistry:Praseodymium(III) fluoride|praseodymium(III) fluoride]] with fluorine gas, producing Na<sub>2</sub>PrF<sub>6</sub>, following which sodium fluoride is removed from the reaction mixture with liquid [[Chemistry:Hydrogen fluoride|hydrogen fluoride]].<ref name="Greenwood1240">Greenwood and Earnshaw, p. 1240–2</ref> Additionally, praseodymium forms a bronze diiodide; like the diiodides of lanthanum, cerium, and [[Chemistry:Gadolinium|gadolinium]], it is a praseodymium(III) [[Physics:Electride|electride]] compound.<ref name="Greenwood1240" />

Praseodymium dissolves readily in dilute [[Chemistry:Sulfuric acid|sulfuric acid]] to form solutions containing the [[Chartreuse (color)|chartreuse]] Pr<sup>3+</sup> ions, which exist as [Pr(H<sub>2</sub>O)<sub>9</sub>]<sup>3+</sup> complexes:<ref name="webelements" /><ref name="Greenwood1242">Greenwood and Earnshaw, pp. 1242–4</ref>

:2 Pr (s) + 3 H<sub>2</sub>SO<sub>4</sub> (aq) → 2 Pr<sup>3+</sup> (aq) + 3 {{chem|SO|4|2-}} (aq) + 3 H<sub>2</sub> (g)

Dissolving praseodymium(IV) compounds in water does not result in solutions containing the yellow Pr<sup>4+</sup> ions;<ref name="SroorEdelmann2012">{{cite book|last1=Sroor|first1=Farid M.A.|title=Encyclopedia of Inorganic and Bioinorganic Chemistry|last2=Edelmann|first2=Frank T.|year=2012|doi=10.1002/9781119951438.eibc2033|chapter=Lanthanides: Tetravalent Inorganic|isbn=978-1-119-95143-8}}</ref> because of the high positive standard reduction potential of the Pr<sup>4+</sup>/Pr<sup>3+</sup> couple at +3.2&nbsp;V, these ions are unstable in aqueous solution, oxidising water and being reduced to Pr<sup>3+</sup>. The value for the Pr<sup>3+</sup>/Pr couple is −2.35&nbsp;V.<ref name="Greenwood1232" /> However, in highly basic aqueous media, Pr<sup>4+</sup> ions can be generated by oxidation with [[Chemistry:Ozone|ozone]].<ref>{{cite journal |title=Stabilization of Praseodymium(IV) and Terbium(IV) in Aqueous Carbonate Solution|author1=Hobart, D.E. |author2= Samhoun, K. |author3= Young, J.P. |author4=Norvell, V.E. |author5= Mamantov, G. |author6= Peterson, J. R. |date=1980 |pages=321–328 |volume=16 |journal=Inorganic and Nuclear Chemistry Letters |doi=10.1016/0020-1650(80)80069-9 |issue=5}}</ref>

Although praseodymium(V) in the bulk state is unknown, the existence of praseodymium in its +5 oxidation state (with the stable electron configuration of the preceding noble gas [[Chemistry:Xenon|xenon]]) under noble-gas matrix isolation conditions was reported in 2016. The species assigned to the +5 state were identified as [PrO<sub>2</sub>]<sup>+</sup>, its O<sub>2</sub> and Ar adducts, and PrO<sub>2</sub>(η<sup>2</sup>-O<sub>2</sub>).<ref>{{Cite journal|last1=Zhang|first1=Qingnan|last2=Hu|first2=Shu-Xian|last3=Qu|first3=Hui|last4=Su|first4=Jing|last5=Wang|first5=Guanjun|last6=Lu|first6=Jun-Bo|last7=Chen|first7=Mohua|last8=Zhou|first8=Mingfei|last9=Li|first9=Jun|date=2016-06-06|title=Pentavalent Lanthanide Compounds: Formation and Characterization of Praseodymium(V) Oxides|journal=Angewandte Chemie International Edition|language=en|volume=55|issue=24|pages=6896–6900|doi=10.1002/anie.201602196|pmid=27100273|issn=1521-3773}}</ref>

=== Organopraseodymium compounds ===
Organopraseodymium compounds are very similar to [[Chemistry:Organolanthanide chemistry|those of the other lanthanides]], as they all share an inability to undergo [[Chemistry:Pi backbonding|π backbonding]]. They are thus mostly restricted to the mostly ionic cyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.<ref name="Greenwood1248">Greenwood and Earnshaw, pp. 1248–9</ref> The coordination chemistry of praseodymium is largely that of the large, electropositive Pr<sup>3+</sup> ion, and is thus largely similar to those of the other early lanthanides La<sup>3+</sup>, Ce<sup>3+</sup>, and Nd<sup>3+</sup>. For instance, like lanthanum, cerium, and neodymium, praseodymium nitrates form both 4:3 and 1:1 complexes with 18-crown-6, whereas the middle lanthanides from [[Chemistry:Promethium|promethium]] to [[Chemistry:Gadolinium|gadolinium]] can only form the 4:3 complex and the later lanthanides from [[Chemistry:Terbium|terbium]] to [[Chemistry:Lutetium|lutetium]] cannot successfully coordinate to all the ligands. Such praseodymium complexes have high but uncertain coordination numbers and poorly defined stereochemistry, with exceptions resulting from exceptionally bulky ligands such as the tricoordinate [Pr{N(SiMe<sub>3</sub>)<sub>2</sub>}<sub>3</sub>]. There are also a few mixed oxides and fluorides involving praseodymium(IV), but it does not have an appreciable coordination chemistry in this oxidation state like its neighbour cerium.<ref name="Greenwood1244">Greenwood and Earnshaw, pp. 1244–8</ref> However, the first example of a molecular complex of praseodymium(IV) has recently been reported.<ref>{{cite journal |title= Accessing the +IV Oxidation State in Molecular Complexes of Praseodymium. |author1=Willauer, A.R. |author2=Palumbo, C.T. |author3=Fadaei-Tirani, F. |author4=Zivkovic, I. |author5=Douair, I. |author6=Maron, L.  |author7=Mazzanti, M. |date=2020 |pages=489–493|volume=142 |journal=Journal of the American Chemical Society |issue=12 |doi=10.1021/jacs.0c01204|pmid=32134644 |s2cid=212564931 |url=http://infoscience.epfl.ch/record/277306 }}</ref>

==Isotopes==
{{main|Physics:Isotopes of praseodymium}}
Praseodymium has only one stable and naturally occurring isotope, <sup>141</sup>Pr. It is thus a [[Mononuclidic element|mononuclidic]] and [[Monoisotopic element|monoisotopic element]], and its [[Physics:Standard atomic weight|standard atomic weight]] can be determined with high precision as it is a constant of nature. This isotope has 82 neutrons, which is a [[Physics:Magic number|magic number]] that confers additional stability.<ref name="Audi">{{NUBASE 2003}}</ref> This isotope is produced in stars through the [[Physics:S-process|s-]] and [[Physics:R-process|r-process]]es (slow and rapid neutron capture, respectively).<ref name="Cameron">{{cite journal|last1=Cameron |first1=A. G. W. |year=1973 |title=Abundance of the Elements in the Solar System |url=http://pubs.giss.nasa.gov/docs/1973/1973_Cameron_1.pdf |journal=Space Science Reviews |volume=15 |issue=1 |pages=121–146 |doi=10.1007/BF00172440 |bibcode=1973SSRv...15..121C |s2cid=120201972 |url-status=dead |archive-url=https://web.archive.org/web/20111021030549/http://pubs.giss.nasa.gov/docs/1973/1973_Cameron_1.pdf |archive-date=2011-10-21 }}</ref> Thirty-eight other radioisotopes have been synthesized. All of these isotopes have half-lives under a day (and most under a minute), with the single exception of <sup>143</sup>Pr with a half-life of 13.6&nbsp;days. Both <sup>143</sup>Pr and <sup>141</sup>Pr occur as fission products of [[Chemistry:Uranium|uranium]]. The primary decay mode of isotopes lighter than <sup>141</sup>Pr is [[Physics:Positron emission|positron emission]] or [[Physics:Electron capture|electron capture]] to [[Physics:Isotopes of cerium|isotopes of cerium]], while that of heavier isotopes is [[Physics:Beta decay|beta decay]] to [[Physics:Isotopes of neodymium|isotopes of neodymium]].<ref name="Audi" />

==History==
[[File:Auer von Welsbach.jpg|upright|thumb|Carl Auer von Welsbach (1858–1929), discoverer of praseodymium in 1885.]]

In 1751, the Swedish mineralogist [[Biography:Axel Fredrik Cronstedt|Axel Fredrik Cronstedt]] discovered a heavy mineral from the mine at Bastnäs, later named [[Chemistry:Cerite|cerite]]. Thirty years later, the fifteen-year-old [[Biography:Wilhelm Hisinger|Wilhelm Hisinger]], from the family owning the mine, sent a sample of it to Carl Scheele, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with [[Biography:Jöns Jacob Berzelius|Jöns Jacob Berzelius]] and isolated a new oxide, which they named ''ceria'' after the [[Astronomy:Dwarf planet|dwarf planet]] [[Astronomy:Ceres (dwarf planet)|Ceres]], which had been discovered two years earlier.<ref name="Emsley120">Emsley, pp. 120–5</ref> Ceria was simultaneously and independently isolated in Germany by [[Biography:Martin Heinrich Klaproth|Martin Heinrich Klaproth]].<ref name="Greenwood1424">Greenwood and Earnshaw, p. 1424</ref> Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist [[Biography:Carl Gustaf Mosander|Carl Gustaf Mosander]], who lived in the same house as Berzelius; he separated out two other oxides, which he named ''lanthana'' and ''didymia''.<ref name= "XI">{{cite journal | doi = 10.1021/ed009p1231 | last = Weeks | first = Mary Elvira | title = The Discovery of the Elements: XI. Some Elements Isolated with the Aid of Potassium and Sodium:Zirconium, Titanium, Cerium and Thorium | journal = The Journal of Chemical Education | date = 1932 | volume = 9 | issue = 7 | pages = 1231–1243 |bibcode = 1932JChEd...9.1231W }}</ref><ref name="Weeks">{{cite book |last1=Weeks |first1=Mary Elvira |title=The discovery of the elements |date= 1956 |publisher=Journal of Chemical Education |location=Easton, PA |url=https://archive.org/details/discoveryoftheel002045mbp |edition=6th }}</ref><ref name= "Virginia">{{cite journal |last1=Marshall |first1=James L. |last2=Marshall |first2=Virginia R. |title=Rediscovery of the elements: The Rare Earths – The Confusing Years |journal= The Hexagon |date=Winter 2015 |pages=72–77 |url=http://www.chem.unt.edu/~jimm/REDISCOVERY%207-09-2018/Hexagon%20Articles/rare%20earths%20II.pdf |access-date=}}</ref> He partially decomposed a sample of [[Chemistry:Cerium nitrate|cerium nitrate]] by roasting it in air and then treating the resulting oxide with dilute [[Chemistry:Nitric acid|nitric acid]]. The metals that formed these oxides were thus named ''lanthanum'' and ''[[Chemistry:Didymium|didymium]]''.<ref>(Berzelius) (1839) [https://archive.org/stream/ComptesRendusAcademieDesSciences0008/ComptesRendusAcadmieDesSciences-Tome008-Janvier-juin1839#page/n361/mode/1up "Nouveau métal"] (New metal), ''Comptes rendus'', ''8'' : 356–357. From p. 356: ''"L'oxide de cérium, extrait de la cérite par la procédé ordinaire, contient à peu près les deux cinquièmes de son poids de l'oxide du nouveau métal qui ne change que peu les propriétés du cérium, et qui s'y tient pour ainsi dire caché. Cette raison a engagé M. Mosander à donner au nouveau métal le nom de ''Lantane''."'' (The oxide of cerium, extracted from cerite by the usual procedure, contains almost two fifths of its weight in the oxide of the new metal, which differs only slightly from the properties of cerium, and which is held in it so to speak "hidden". This reason motivated Mr. Mosander to give to the new metal the name ''Lantane''.)</ref><ref>(Berzelius) (1839) [https://books.google.com/books?id=dF1KiX7MbSMC&pg=PA390 "Latanium — a new metal,"] ''Philosophical Magazine'', new series, '''14''' : 390–391.</ref>

While lanthanum turned out to be a pure element, didymium was not and turned out to be only a mixture of all the stable early lanthanides from praseodymium to [[Chemistry:Europium|europium]], as had been suspected by [[Biography:Marc Delafontaine|Marc Delafontaine]] after spectroscopic analysis, though he lacked the time to pursue its separation into its constituents. The heavy pair of [[Chemistry:Samarium|samarium]] and europium were only removed in 1879 by [[Biography:Paul-Émile Lecoq de Boisbaudran|Paul-Émile Lecoq de Boisbaudran]] and it was not until 1885 that [[Biography:Carl Auer von Welsbach|Carl Auer von Welsbach]] separated didymium into praseodymium and neodymium.<ref name="Lost">{{cite book|ref=Fontani|last1=Fontani|first1=Marco|last2=Costa|first2=Mariagrazia|last3=Orna|first3=Virginia|title=The Lost Elements: The Periodic Table's Shadow Side|publisher=Oxford University Press|year=2014|url=https://books.google.com/books?id=Ck9jBAAAQBAJ&pg=PA122|pages=122–123|isbn=978-0-19-938334-4}}</ref> Von Welsbach confirmed the separation by spectroscopic analysis, but the products were of relatively low purity. Since neodymium was a larger constituent of didymium than praseodymium, it kept the old name with disambiguation, while praseodymium was distinguished by the leek-green colour of its salts (Greek πρασιος, "leek green").<ref name="Greenwood1229" /> The composite nature of didymium had previously been suggested in 1882 by Bohuslav Brauner, who did not experimentally pursue its separation.<ref name="Lost_p40">{{cite book|ref=Fontani|last1=Fontani|first1=Marco|last2=Costa|first2=Mariagrazia|last3=Orna|first3=Virginia|title=The Lost Elements: The Periodic Table's Shadow Side|url=https://books.google.com/books?id=Ck9jBAAAQBAJ&pg=PA40|publisher=Oxford University Press|year=2014|page=40|isbn=978-0-19-938334-4}}</ref>

==Occurrence and production==
Praseodymium is not particularly rare, despite it being in the rare-earth metals, making up 9.2&nbsp;mg/kg of the Earth's crust. This value is between those of [[Chemistry:Thorium|thorium]] (9.6&nbsp;mg/kg) and [[Chemistry:Samarium|samarium]] (7.05&nbsp;mg/kg), and makes praseodymium the fourth-most abundant of the lanthanides, behind cerium (66.5&nbsp;mg/kg), neodymium (41.5&nbsp;mg/kg), and lanthanum (39&nbsp;mg/kg); it is less abundant than the [[Chemistry:Rare-earth element|rare-earth element]]s [[Chemistry:Yttrium|yttrium]] (33&nbsp;mg/kg) and [[Chemistry:Scandium|scandium]] (22&nbsp;mg/kg).<ref name="Greenwood1229">Greenwood and Earnshaw, p. 1229–32</ref> Instead, praseodymium's classification as a rare-earth metal comes from its rarity relative to "common earths" such as lime and magnesia, the few known minerals containing it for which extraction is commercially viable, as well as the length and complexity of extraction.<ref name="patnaik">{{cite book | last =Patnaik | first =Pradyot | date = 2003 | title =Handbook of Inorganic Chemical Compounds | publisher = McGraw-Hill | pages = 444–446| isbn =978-0-07-049439-8 | url= {{Google books |plainurl=yes |id=Xqj-TTzkvTEC |page=243 }} | access-date = 2009-06-06}}</ref> Although not particularly rare, praseodymium is never found as a dominant rare earth in praseodymium-bearing minerals. It is always preceded by cerium and lanthanum and usually also by neodymium.<ref>
{{cite web |url=https://www.mindat.org/ |title=Mindat.org |author=Hudson Institute of Mineralogy |date=1993–2018 |website=www.mindat.org |access-date=14 January 2018}}</ref>

[[File:Monazite acid cracking process.svg|frameless|center|730px]]
The Pr<sup>3+</sup> ion is similar in size to the early lanthanides of the cerium group (those from lanthanum up to [[Chemistry:Samarium|samarium]] and [[Chemistry:Europium|europium]]) that immediately follow in the periodic table, and hence it tends to occur along with them in [[Chemistry:Phosphate|phosphate]], [[Chemistry:Silicate|silicate]] and [[Chemistry:Carbonate|carbonate]] minerals, such as [[Chemistry:Monazite|monazite]] (M<sup>III</sup>PO<sub>4</sub>) and [[Chemistry:Bastnäsite|bastnäsite]] (M<sup>III</sup>CO<sub>3</sub>F), where M refers to all the rare-earth metals except scandium and the radioactive [[Chemistry:Promethium|promethium]] (mostly Ce, La, and Y, with somewhat less Nd and Pr).<ref name="Greenwood1229" /> Bastnäsite is usually lacking in [[Chemistry:Thorium|thorium]] and the heavy lanthanides, and the purification of the light lanthanides from it is less involved. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, evolving carbon dioxide, [[Chemistry:Hydrogen fluoride|hydrogen fluoride]], and [[Chemistry:Silicon tetrafluoride|silicon tetrafluoride]]. The product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.<ref name="Greenwood1229" />

The procedure for monazite, which usually contains all the rare earth, as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earth. The acidic filtrates are partially neutralized with [[Chemistry:Sodium hydroxide|sodium hydroxide]] to pH 3–4, during which thorium precipitates as hydroxide and is removed. The solution is treated with [[Chemistry:Ammonium oxalate|ammonium oxalate]] to convert rare earth to their insoluble [[Chemistry:Oxalate|oxalate]]s, the oxalates are converted to oxides by annealing, and the oxides are dissolved in nitric acid. This last step excludes one of the main components, [[Chemistry:Cerium|cerium]], whose oxide is insoluble in HNO<sub>3</sub>.<ref name="Patnaik">{{harvnb|Patnaik|2007|pp=[https://books.google.com/books?id=-CRRJBVv5d0C&pg=PA478 478–479]}}.</ref> Care must be taken when handling some of the residues as they contain [[Physics:Radium-228|<sup>228</sup>Ra]], the daughter of <sup>232</sup>Th, which is a strong gamma emitter.<ref name="Greenwood1229" />

Praseodymium may then be separated from the other lanthanides via ion-exchange chromatography, or by using a solvent such as [[Chemistry:Tributyl phosphate|tributyl phosphate]] where the solubility of Ln<sup>3+</sup> increases as the atomic number increases. If ion-exchange chromatography is used, the mixture of lanthanides is loaded into one column of cation-exchange resin and Cu<sup>2+</sup> or Zn<sup>2+</sup> or Fe<sup>3+</sup> is loaded into the other. An aqueous solution of a complexing agent, known as the eluant (usually triammonium edtate), is passed through the columns, and Ln<sup>3+</sup> is displaced from the first column and redeposited in a compact band at the top of the column before being re-displaced by {{chem|NH|4|+}}. The [[Physics:Gibbs free energy|Gibbs free energy]] of formation for Ln(edta·H) complexes increases along with the lanthanides by about one quarter from Ce<sup>3+</sup> to Lu<sup>3+</sup>, so that the Ln<sup>3+</sup> cations descend the development column in a band and are fractionated repeatedly, eluting from heaviest to lightest. They are then precipitated as their insoluble oxalates, burned to form the oxides, and then reduced to metals.<ref name="Greenwood1229" />

==Applications==
Leo Moser (not to be confused with [[Biography:Leo Moser|the mathematician of the same name]]), son of Ludwig Moser, founder of the Moser Glassworks in what is now Karlovy Vary in the Czech Republic, investigated the use of praseodymium in glass coloration in the late 1920s, yielding a yellow-green glass given the name "Prasemit". However, at that time far cheaper colorants could give a similar color, so Prasemit was not popular, few pieces were made, and examples are now extremely rare. Moser also blended praseodymium with neodymium to produce "Heliolite" glass ("Heliolit" in [[Social:German language|German]]),<!--http://books.google.de/books?id=36dRAAAAMAAJ&q=praseodymium+glass+moser&dq=praseodymium+glass+moser&hl=de&ei=Ptt0TLLYE5KHswalhr2IBg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CD4Q6AEwAQ--> which was more widely accepted. The first enduring commercial use of purified praseodymium, which continues today, is in the form of a yellow-orange "Praseodymium Yellow" stain for ceramics, which is a solid solution in the [[Chemistry:Zirconium(IV) silicate|zircon]] lattice. This stain has no hint of green in it; by contrast, at sufficiently high loadings, praseodymium glass is distinctly green rather than pure yellow.<ref>{{cite journal | last1 = Kreidl | first1 = Norbert J. | title = RARE EARTHS* | journal = Journal of the American Ceramic Society | volume = 25 | pages = 141–143 | date = 1942 | doi = 10.1111/j.1151-2916.1942.tb14363.x | issue = 5}}</ref>

Like many other lanthanides, praseodymium's shielded f-orbitals allow for long [[Physics:Excited state|excited state]] lifetimes and high [[Physics:Luminescence|luminescence]] yields. Pr<sup>3+</sup> as a [[Physics:Doping (semiconductor)|dopant]] ion therefore sees many applications in [[Physics:Optics|optics]] and [[Physics:Photonics|photonics]]. These include [[Physics:Pr:YLF laser|DPSS-lasers]], single-mode fiber [[Physics:Optical amplifier|optical amplifier]]s,<ref>{{cite journal|last1=Jha|first1=A.|last2=Naftaly|first2=M.|last3=Jordery|first3=S.|last4=Samson|first4=B. N.|last5=Taylor|first5=E. R.|last6=Hewak|first6=D.|last7=Payne|first7=D. N.|last8=Poulain|first8=M.|last9=Zhang|first9=G.|display-authors=4|date=1995|title=Design and fabrication of Pr3+-doped fluoride glass optical fibres for efficient 1.3 mu m amplifiers|url=https://eprints.soton.ac.uk/78174/1/918.pdf|journal=Pure and Applied Optics: Journal of the European Optical Society Part A|volume=4|issue=4|pages=417|bibcode=1995PApOp...4..417J|doi=10.1088/0963-9659/4/4/019}}</ref> fiber lasers,<ref>{{Cite journal|last1=Smart|first1=R.G.|last2=Hanna|first2=D.C.|last3=Tropper|first3=A.C.|last4=Davey|first4=S.T.|last5=Carter|first5=S.F.|last6=Szebesta|first6=D.|date=1991|title=Cw room temperature upconversion lasing at blue, green and red wavelengths in infrared-pumped Pr3+-doped fluoride fibre|url=https://digital-library.theiet.org/content/journals/10.1049/el_19910817|journal=Electronics Letters|language=en|volume=27|issue=14|pages=1307|doi=10.1049/el:19910817|bibcode=1991ElL....27.1307S}}</ref> [[Physics:Upconverting nanoparticles|upconverting nanoparticles]]<ref>{{Cite journal|last1=de Prinse|first1=Thomas J.|last2=Karami|first2=Afshin|last3=Moffatt|first3=Jillian E.|last4=Payten|first4=Thomas B.|last5=Tsiminis|first5=Georgios|last6=Teixeira|first6=Lewis Da Silva|last7=Bi|first7=Jingxiu|last8=Kee|first8=Tak W.|last9=Klantsataya|first9=Elizaveta|last10=Sumby|first10=Christopher J.|last11=Spooner|first11=Nigel A.|date=2021|title=Dual Laser Study of Non‐Degenerate Two Wavelength Upconversion Demonstrated in Sensitizer‐Free NaYF 4 :Pr Nanoparticles|url=https://onlinelibrary.wiley.com/doi/10.1002/adom.202001903|journal=Advanced Optical Materials|volume=9|issue=7|language=en|pages=2001903|doi=10.1002/adom.202001903|s2cid=234059121|issn=2195-1071|hdl=2440/139814|hdl-access=free}}</ref><ref>{{Cite journal|last1=Kolesov|first1=Roman|last2=Reuter|first2=Rolf|last3=Xia|first3=Kangwei|last4=Stöhr|first4=Rainer|last5=Zappe|first5=Andrea|last6=Wrachtrup|first6=Jörg|date=2011-10-31|title=Super-resolution upconversion microscopy of praseodymium-doped yttrium aluminum garnet nanoparticles|url=https://link.aps.org/doi/10.1103/PhysRevB.84.153413|journal=Physical Review B|language=en|volume=84|issue=15|pages=153413|doi=10.1103/PhysRevB.84.153413|bibcode=2011PhRvB..84o3413K|issn=1098-0121}}</ref> as well as activators in red, green, blue, and ultraviolet phosphors.<ref name="Ullmann" /> Silicate crystals doped with praseodymium ions have also been used to [[Physics:Slow light|slow a light pulse]] down to a few hundred meters per second.<ref name="ANUPressStopLight">{{cite web|title=ANU team stops light in quantum leap|url=http://info.anu.edu.au/ovc/Media/Media_Releases/2005/August/290805_stop_light|access-date=18 May 2009}}</ref>

As the lanthanides are so similar, praseodymium can substitute for most other lanthanides without significant loss of function, and indeed many applications such as [[Chemistry:Mischmetal|mischmetal]] and [[Chemistry:Ferrocerium|ferrocerium]] alloys involve variable mixes of several lanthanides, including small quantities of praseodymium. The following more modern applications involve praseodymium specifically or at least praseodymium in a small subset of the lanthanides:<ref name="Ullmann" />
* In combination with neodymium, another rare-earth element, praseodymium is used to create high-power magnets notable for their strength and durability.<ref name="IAMGOLD">[http://www.iamgold.com/files/REE101_April_2012.pdf Rare Earth Elements 101] {{webarchive|url=https://web.archive.org/web/20131122140504/http://www.iamgold.com/files/REE101_April_2012.pdf |date=2013-11-22 }}, IAMGOLD Corporation, April 2012, pp. 5, 7.</ref> In general, most alloys of the cerium-group rare earths ([[Chemistry:Lanthanum|lanthanum]] through [[Chemistry:Samarium|samarium]]) with 3d [[Chemistry:Transition metal|transition metal]]s give extremely stable magnets that are often used in small equipment, such as motors, printers, watches, headphones, loudspeakers, and magnetic storage.<ref name="Ullmann">{{Ullmann|volume=31|page=183–227|last1=McGill|first1=Ian|contribution=Rare Earth Elements|doi=10.1002/14356007.a22_607}}</ref>
*Praseodymium–[[Chemistry:Nickel|nickel]] intermetallic (PrNi<sub>5</sub>) has such a strong [[Physics:Magnetic refrigeration#The magnetocaloric effect|magnetocaloric effect]] that it has allowed scientists to approach within one thousandth of a degree of [[Physics:Absolute zero|absolute zero]].<ref name="Emsley423" />
* As an [[Chemistry:Alloy|alloy]]ing agent with [[Chemistry:Magnesium|magnesium]] to create high-strength metals that are used in [[Engineering:Aircraft engine|aircraft engine]]s; [[Chemistry:Yttrium|yttrium]] and [[Chemistry:Neodymium|neodymium]] are also viable substitutes.<ref>{{cite book| first = L. L. |last = Rokhlin | title = Magnesium alloys containing rare earth metals: structure and properties| publisher = CRC Press| date = 2003| isbn =978-0-415-28414-1}}</ref><ref>{{cite journal | last1 = Suseelan Nair | first1 = K. | last2 = Mittal | first2 = M. C. | title = Rare Earths in Magnesium Alloys | journal = Materials Science Forum | volume = 30 | pages = 89–104 | date = 1988 | doi = 10.4028/www.scientific.net/MSF.30.89| s2cid = 136992837 }}</ref>
* Praseodymium is present in the rare-earth mixture whose fluoride forms the core of carbon arc lights, which are used in the motion picture industry for studio lighting and projector lights.<ref name="Emsley423">Emsley, pp. 423–5</ref>
* Praseodymium [[Chemistry:Chemical compound|compounds]] give [[Chemistry:Glass|glass]]es, [[Engineering:Vitreous enamel|enamels]] and ceramics a [[Yellow|yellow]] color.<ref name="CRC" /><ref name="Ullmann" />
* Praseodymium is a component of [[Chemistry:Didymium|didymium]] glass, which is used to make certain types of [[Chemistry:Welding|welder]]'s and glass blower's [[Goggles|goggles]].<ref name="CRC" />
* Praseodymium oxide in solid solution with ceria or [[Chemistry:Ceria-zirconia|ceria-zirconia]] has been used as an oxidation [[Chemistry:Catalyst|catalyst]].<ref>{{cite journal| doi = 10.1021/jp0768524| title = Nanostructured Praseodymium Oxide: Preparation, Structure, and Catalytic Properties| date = 2008| display-authors = 4| author = Borchert, Y.| author2 = Sonstrom, P.| author3 = Wilhelm, M.| author4 = Borchert, H.| author5 = Baumer, M.| journal = Journal of Physical Chemistry C| volume = 112| pages = 3054| issue = 8}}</ref>

Due to its role in permanent magnets used for wind turbines, it has been argued that praseodymium will be one of the main objects of geopolitical competition in a world running on renewable energy. However, this perspective has been criticized for failing to recognize that most wind turbines do not use permanent magnets and for underestimating the power of economic incentives for expanded production.<ref>{{Cite journal|last=Overland|first=Indra|date=2019-03-01|title=The geopolitics of renewable energy: Debunking four emerging myths|journal=Energy Research & Social Science|volume=49|pages=36–40|doi=10.1016/j.erss.2018.10.018|issn=2214-6296|doi-access=free}}</ref><ref name="Klinger">{{cite book |last1=Klinger |first1=Julie Michelle |title=Rare earth frontiers : from terrestrial subsoils to lunar landscapes |date=2017 |publisher=Cornell University Press |location=Ithaca, NY |isbn=978-1501714603 |jstor=10.7591/j.ctt1w0dd6d }}</ref>

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==Biological role and precautions==
The early lanthanides have been found to be essential to some methanotrophic bacteria living in [[Earth:Mudpot|volcanic mudpots]], such as ''[[Biology:Methylacidiphilum fumariolicum|Methylacidiphilum fumariolicum]]'': lanthanum, cerium, praseodymium, and neodymium are about equally effective.<ref>{{cite journal |doi=10.1111/1462-2920.12249 |pmid=24034209 |title=Rare earth metals are essential for methanotrophic life in volcanic mudpots |date=2013 |last1=Pol |first1=Arjan |last2=Barends |first2=Thomas R. M. |last3=Dietl |first3=Andreas |last4=Khadem |first4=Ahmad F. |last5=Eygensteyn |first5=Jelle |last6=Jetten |first6=Mike S. M. |last7=Op Den Camp |first7=Huub J. M. |journal=Environmental Microbiology |volume=16 |issue=1 |pages=255–64}}</ref><ref>{{cite journal | last1=Kang | first1=L. | last2=Shen | first2=Z. | last3=Jin | first3=C. | title=Neodymium cations Nd<sup>3+</sup> were transported to the interior of ''Euglena gracilis'' | issue=277 | journal=Chin. Sci. Bull. | volume=45 | pages=585–592 | date=2000 | doi=10.1007/BF02886032| bibcode=2000ChSBu..45..585K | s2cid=95983365 }}</ref> Praseodymium is otherwise not known to have a biological role in any other organisms, but it is not very toxic either. Intravenous injection of rare earths into animals has been known to impair liver function, but the main side effects from inhalation of rare-earth oxides in humans come from radioactive [[Chemistry:Thorium|thorium]] and [[Chemistry:Uranium|uranium]] impurities.<ref name="Ullmann" />
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==References==
{{reflist}}

==Bibliography==
*{{cite book|author=Emsley, John|title=Nature's Building Blocks: An A-Z Guide to the Elements|date=2011|publisher=[[Organization:Oxford University Press|Oxford University Press]]|isbn=978-0-19-960563-7}}

== Further reading ==
* R. J. Callow, ''The Industrial Chemistry of the Lanthanons, Yttrium, Thorium, and Uranium'', Pergamon Press, 1967.
* Bouhani, H (2020). "Engineering the magnetocaloric properties of PrVO3 epitaxial oxide thin films by strain effects". Applied Physics Letters. 117 (7). arXiv:2008.09193. doi:10.1063/5.0021031.

== External links ==
{{Commons|Praseodymium}}
* [http://www.webelements.com/webelements/elements/text/Pr/index.html WebElements.com—Praseodymium]
* [http://education.jlab.org/itselemental/ele059.html It's Elemental—The Element Praseodymium]
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{{Periodic table (navbox)}}
{{Praseodymium compounds}}


[[Category:Praseodymium| ]]
[[Category:Chemical elements]]
[[Category:Lanthanides]]
[[Category:Reducing agents]]

{{Sourceattribution|Praseodymium}}