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Praseodymium is a chemical element; it has symbol Pr and atomic number 59. It is the third member of the lanthanide series and is considered one of the . It is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in 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 of the Earth's crust, an abundance similar to that of boron. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare-earth oxide residue he called didymium from a residue he called "lanthana", in turn separated from cerium salts. In 1885, the Austrian chemist Carl Auer von Welsbach separated didymium into two elements that gave salts of different colours, which he named praseodymium and neodymium. The name praseodymium comes from the Ancient Greek πράσινος (), meaning 'leek-green', and δίδυμος () 'twin'.
Like most rare-earth elements, praseodymium most readily forms the +3 oxidation state, which is the only stable state in aqueous solution, although the +4 oxidation state is known in some solid compounds and, uniquely among the lanthanides, the +5 oxidation state is attainable at low temperatures. 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.
Neutral praseodymium's 59 electrons are arranged in the configuration Xe4f36s2. Like most other lanthanides, praseodymium usually uses only three electrons as valence electrons, as the remaining 4f electrons are too strongly bound to engage in bonding: 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 penetration increases with higher ionic charge. Even so, praseodymium can in some compounds lose a fourth valence electron because it is 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.Greenwood and Earnshaw, pp. 1232–8
Similarly to the other early lanthanides, praseodymium has a double hexagonal close-packed crystal structure at room temperature, called the alpha phase (α-Pr). At it transforms to a different Allotropy that has a body-centered cubic structure (β-Pr), and it melts at .
Praseodymium, like all of the lanthanides, is paramagnetic at room temperature. (2025). 9781118211496, John Wiley & Sons. ISBN 9781118211496 Unlike some other rare-earth metals, which show antiferromagnetic or ferromagnetic ordering at low temperatures, praseodymium is paramagnetic at all temperatures above 1 K.
This may be reduced to praseodymium(III) oxide with hydrogen gas. Praseodymium(IV) oxide, , 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 °C and 282 bar or by disproportionation of in boiling acetic acid. The reactivity of praseodymium conforms to periodic trends, as it is one of the first and thus one of the largest lanthanides. At 1000 °C, many praseodymium oxides with composition PrO2− x exist as disordered, nonstoichiometric phases with 0 < x < 0.25, but at 400–700 °C the oxide defects are instead ordered, creating phases of the general formula with n = 4, 7, 9, 10, 11, 12, and ∞. These phases PrO y 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.
Praseodymium is an electropositive element and reacts slowly with cold water and quite quickly with hot water to form praseodymium(III) hydroxide:
Praseodymium metal reacts with all the stable to form trihalides:
Praseodymium dissolves readily in dilute sulfuric acid to form solutions containing the chartreuse ions, which exist as complexes:
Dissolving praseodymium(IV) compounds in water does not result in solutions containing the yellow ions; (2025). 9781119951438 ISBN 9781119951438 because of the high positive standard reduction potential of the/ couple at +3.2 V, these ions are unstable in aqueous solution, oxidising water and being reduced to . The value for the /Pr couple is −2.35 V. However, in highly basic aqueous media, ions can be generated by oxidation with ozone.
Praseodymium(V) has been observed by matrix isolation (in 2016) and in the bulk state (in 2025). The existence of praseodymium in its +5 oxidation state (with the stable electron configuration of the preceding noble gas xenon) under noble-gas matrix isolation conditions was reported in 2016. The species assigned to the +5 state were identified as , its and Ar adducts, and . Further, in 2025, a neutral compound , formally Pr(V) but with an inverted ligand field, was isolated and characterized crystallographically at low temperatures.
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 europium, as had been suspected by Marc Delafontaine after spectroscopic analysis, though he lacked the time to pursue its separation into its constituents. The heavy pair of samarium and europium were only removed in 1879 by Paul-Émile Lecoq de Boisbaudran and it was not until 1885 that Carl Auer von Welsbach separated didymium into praseodymium and neodymium. 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").Greenwood and Earnshaw, p. 1229–32 The composite nature of didymium had previously been suggested in 1882 by Bohuslav Brauner, who did not experimentally pursue its separation.
The Pr3+ ion is similar in size to the early lanthanides of the cerium group (those from lanthanum up to samarium and europium) that immediately follow in the periodic table, and hence it tends to occur along with them in phosphate, silicate and carbonate minerals, such as monazite (MIIIPO4) and bastnäsite (MIIICO3F), where M refers to all the rare-earth metals except scandium and the radioactive promethium (mostly Ce, La, and Y, with somewhat less Nd and Pr). Bastnäsite is usually lacking in 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, hydrogen fluoride, and silicon tetrafluoride. The product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.
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 sodium hydroxide to pH 3–4, during which thorium precipitates as hydroxide and is removed. The solution is treated with ammonium oxalate to convert rare earth to their insoluble , 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, cerium, whose oxide is insoluble in HNO3. Care must be taken when handling some of the residues as they contain 228Ra, the daughter of 232Th, which is a strong gamma emitter.
Praseodymium may then be separated from the other lanthanides via ion-exchange chromatography, or by using a solvent such as tributyl phosphate where the solubility of Ln3+ 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 Cu2+ or Zn2+ or Fe3+ 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 Ln3+ is displaced from the first column and redeposited in a compact band at the top of the column before being re-displaced by . The Gibbs free energy of formation for Ln(edta·H) complexes increases along with the lanthanides by about one quarter from Ce3+ to Lu3+, so that the Ln3+ 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.
Like many other lanthanides, praseodymium's shielded allow for long excited state lifetimes and high luminescence yields. Pr3+ as a dopant ion therefore sees many applications in optics and photonics. These include , single-mode fiber optical amplifiers, fiber lasers, upconverting nanoparticles as well as activators in red, green, blue, and ultraviolet phosphors. Silicate crystals doped with praseodymium ions have also been used to slow light down to a few hundred meters per second.
As the lanthanides are so similar, praseodymium can substitute for most other lanthanides without significant loss of function, and indeed many applications such as mischmetal and 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:
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. (2025). 9781501714603, Cornell University Press. ISBN 9781501714603
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