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Praseodymium, 59Pr
Pronunciation /ˌprzəˈdɪmiəm/ [1] (PRAY-zee-ə-DIM-ee-əm)
Appearancegrayish white
Standard atomic weight Ar°(Pr)
Praseodymium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)59
Group f-block groups (no number)
Period period 6
Block   f-block
Electron configuration [ Xe ] 4f3 6s2
Electrons per shell2, 8, 18, 21, 8, 2
Physical properties
Phase at  STP solid
Melting point 1204  K (931 °C,1708 °F) [4]
Boiling point 3403 K(3130 °C,5666 °F)
Density (at 20° C)6.773 g/cm3 [4]
when liquid (at  m.p.)6.50 g/cm3
Heat of fusion 6.89  kJ/mol
Heat of vaporization 331 kJ/mol
Molar heat capacity 27.20 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)17711973(2227)(2571)(3054)(3779)
Atomic properties
Oxidation states 0, [5] +1, [6] +2, +3, +4, +5 (a mildly basic oxide)
Electronegativity Pauling scale: 1.13
Ionization energies
  • 1st: 527 kJ/mol
  • 2nd: 1020 kJ/mol
  • 3rd: 2086 kJ/mol
Atomic radius empirical:182  pm
Covalent radius 203±7 pm
Praseodymium spectrum visible.png
Spectral lines of praseodymium
Other properties
Natural occurrence primordial
Crystal structure double hexagonal close-packed (dhcp)(hP4)
Lattice constants
a = 0.36723 nm
c = 1.18328 nm (at 20 °C) [4]
Thermal expansion 4.5×10−6/K (at 20 °C) [4] [lower-alpha 1]
Thermal conductivity 12.5 W/(m⋅K)
Electrical resistivity poly: 0.700 µΩ⋅m(at r.t.)
Magnetic ordering paramagnetic [7]
Molar magnetic susceptibility +5010.0×10−6 cm3/mol(293 K) [8]
Young's modulus 37.3 GPa
Shear modulus 14.8 GPa
Bulk modulus 28.8 GPa
Speed of sound thin rod2280 m/s(at 20 °C)
Poisson ratio 0.281
Vickers hardness 250–745 MPa
Brinell hardness 250–640 MPa
CAS Number 7440-10-0
Discovery Carl Auer von Welsbach (1885)
Isotopes of praseodymium
Main isotopes [9] Decay
abun­dance half-life (t1/2) mode pro­duct
141Pr100% stable
142Pr synth 19.12 h β 142Nd
ε 142Ce
143Prsynth13.57 dβ 143Nd
Symbol category class.svg  Category: Praseodymium
| references

Praseodymium is a chemical element; it has symbol Pr and the atomic number 59. It is the third member of the lanthanide series and is considered one of the rare-earth metals. 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 (prasinos), meaning 'leek-green', and δίδυμος (didymos) '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 in 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 lanthanide series, and a member of the rare-earth metals. In the periodic table, it appears between the lanthanides cerium to its left and neodymium to its right, and above the actinide protactinium. It is a ductile metal with a hardness comparable to that of silver. [10] Praseodymium is calculated to have a very large atomic radius; with a radius of 247 pm, barium, rubidium and caesium are larger. [11] However, observationally, it is usually 185 pm. [12]

Neutral praseodymium's 59 electrons are arranged in the configuration [Xe]4f36s2. 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. [13]

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 795 °C (1,068 K) it transforms to a different allotrope that has a body-centered cubic structure (β-Pr), and it melts at 931 °C (1,204 K). [4]

Praseodymium, like all of the lanthanides, is paramagnetic at room temperature. [14] Unlike some other rare-earth metals, which show antiferromagnetic or ferromagnetic ordering at low temperatures, praseodymium is paramagnetic at all temperatures above 1 K. [7]

Chemical properties

Praseodymium(III) hydroxide Praseodymium(III) hydroxide.jpg
Praseodymium(III) hydroxide

Praseodymium metal tarnishes slowly in air, forming a spalling green oxide layer like iron rust; a centimetre-sized sample of praseodymium metal corrodes completely in about a year. [15] It burns readily at 150 °C to form praseodymium(III,IV) oxide, a nonstoichiometric compound approximating to Pr6O11: [16]

12 Pr + 11 O2 → 2 Pr6O11

This may be reduced to praseodymium(III) oxide (Pr2O3) with hydrogen gas. [17] Praseodymium(IV) oxide, PrO2, 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 [17] or by disproportionation of Pr6O11 in boiling acetic acid. [18] [19] The reactivity of praseodymium conforms to periodic trends, as it is one of the first and thus one of the largest lanthanides. [13] 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 PrnO2n−2 with n = 4, 7, 9, 10, 11, 12, and ∞. These phases PrOy 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. [20]

Praseodymium is an electropositive element and reacts slowly with cold water and quite quickly with hot water to form praseodymium(III) hydroxide: [16]

2 Pr (s) + 6 H2O (l) → 2 Pr(OH)3 (aq) + 3 H2 (g)

Praseodymium metal reacts with all the stable halogens to form trihalides: [16]

2 Pr (s) + 3 F2 (g) → 2 PrF3 (s) [green]
2 Pr (s) + 3 Cl2 (g) → 2 PrCl3 (s) [green]
2 Pr (s) + 3 Br2 (g) → 2 PrBr3 (s) [green]
2 Pr (s) + 3 I2 (g) → 2 PrI3 (s)

The tetrafluoride, PrF4, is also known, and is produced by reacting a mixture of sodium fluoride and praseodymium(III) fluoride with fluorine gas, producing Na2PrF6, following which sodium fluoride is removed from the reaction mixture with liquid hydrogen fluoride. [21] Additionally, praseodymium forms a bronze diiodide; like the diiodides of lanthanum, cerium, and gadolinium, it is a praseodymium(III) electride compound. [21]

Praseodymium dissolves readily in dilute sulfuric acid to form solutions containing the chartreuse Pr3+ ions, which exist as [Pr(H2O)9]3+ complexes: [16] [22]

2 Pr (s) + 3 H2SO4 (aq) → 2 Pr3+ (aq) + 3 SO2−
(aq) + 3 H2 (g)

Dissolving praseodymium(IV) compounds in water does not result in solutions containing the yellow Pr4+ ions; [23] because of the high positive standard reduction potential of the Pr4+/Pr3+ couple at +3.2 V, these ions are unstable in aqueous solution, oxidising water and being reduced to Pr3+. The value for the Pr3+/Pr couple is −2.35 V. [24] However, in highly basic aqueous media, Pr4+ ions can be generated by oxidation with ozone. [25]

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 xenon) under noble-gas matrix isolation conditions was reported in 2016. The species assigned to the +5 state were identified as [PrO2]+, its O2 and Ar adducts, and PrO22-O2). [26]

Organopraseodymium compounds

Organopraseodymium compounds are very similar to those of the other lanthanides, as they all share an inability to undergo 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. [27] The coordination chemistry of praseodymium is largely that of the large, electropositive Pr3+ ion, and is thus largely similar to those of the other early lanthanides La3+, Ce3+, and Nd3+. 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 promethium to gadolinium can only form the 4:3 complex and the later lanthanides from terbium to 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(SiMe3)2}3]. 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. [28] However, the first example of a molecular complex of praseodymium(IV) has recently been reported. [29]


Praseodymium has only one stable and naturally occurring isotope, 141Pr. It is thus a mononuclidic and monoisotopic element, and its standard atomic weight can be determined with high precision as it is a constant of nature. This isotope has 82 neutrons, which is a magic number that confers additional stability. [30] This isotope is produced in stars through the s- and r-processes (slow and rapid neutron capture, respectively). [31] 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 143Pr with a half-life of 13.6 days. Both 143Pr and 141Pr occur as fission products of uranium. The primary decay mode of isotopes lighter than 141Pr is positron emission or electron capture to isotopes of cerium, while that of heavier isotopes is beta decay to isotopes of neodymium. [30]


Carl Auer von Welsbach (1858-1929), discoverer of praseodymium in 1885. Auer von Welsbach.jpg
Carl Auer von Welsbach (1858–1929), discoverer of praseodymium in 1885.

In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered a heavy mineral from the mine at Bastnäs, later named cerite. Thirty years later, the fifteen-year-old 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 Jöns Jacob Berzelius and isolated a new oxide, which they named ceria after the dwarf planet Ceres, which had been discovered two years earlier. [32] Ceria was simultaneously and independently isolated in Germany by Martin Heinrich Klaproth. [33] Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist Carl Gustaf Mosander, who lived in the same house as Berzelius; he separated out two other oxides, which he named lanthana and didymia. [34] [35] [36] He partially decomposed a sample of cerium nitrate by roasting it in air and then treating the resulting oxide with dilute nitric acid. The metals that formed these oxides were thus named lanthanum and didymium . [37] [38]

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. [39] 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"). [40] The composite nature of didymium had previously been suggested in 1882 by Bohuslav Brauner, who did not experimentally pursue its separation. [41]

Occurrence and production

Praseodymium is not particularly rare, despite it being in the rare-earth metals, making up 9.2 mg/kg of the Earth's crust. [42] 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. [43] 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. [44]

Monazite acid cracking process.svg

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). [40] 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. [40]

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 oxalates, 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. [45] Care must be taken when handling some of the residues as they contain 228Ra, the daughter of 232Th, which is a strong gamma emitter. [40]

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 NH+
. 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. [40]


Leo Moser (not to be confused with 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 German), 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 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. [46]

Like many other lanthanides, praseodymium's shielded f-orbitals 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 DPSS-lasers, single-mode fiber optical amplifiers, [47] fiber lasers, [48] upconverting nanoparticles [49] [50] as well as activators in red, green, blue, and ultraviolet phosphors. [51] Silicate crystals doped with praseodymium ions have also been used to slow a light pulse down to a few hundred meters per second. [52]

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: [51]

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. [58] [59]

GHS labelling:
P222, P231, P422 [60]
NFPA 704 (fire diamond)
NFPA 704.svgHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g. nitroglycerinSpecial hazards (white): no code

Biological role and precautions

The early lanthanides have been found to be essential to some methanotrophic bacteria living in volcanic mudpots, such as Methylacidiphilum fumariolicum : lanthanum, cerium, praseodymium, and neodymium are about equally effective. [61] [62] 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 thorium and uranium impurities. [51]


  1. The thermal expansion is highly anisotropic: the parameters (at 20 °C) for each crystal axis are αa = 1.4×10−6/K, αc = 10.8×10−6/K, and αaverage = αV/3 = 4.5×10−6/K.

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<span class="mw-page-title-main">Erbium</span> Chemical element, symbol Er and atomic number 68

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<span class="mw-page-title-main">Lanthanum</span> Chemical element, symbol La and atomic number 57

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<span class="mw-page-title-main">Lutetium</span> Chemical element, symbol Lu and atomic number 71

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<span class="mw-page-title-main">Neodymium</span> Chemical element, symbol Nd and atomic number 60

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<span class="mw-page-title-main">Promethium</span> Chemical element, symbol Pm and atomic number 61

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<span class="mw-page-title-main">Thorium</span> Chemical element, symbol Th and atomic number 90

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<span class="mw-page-title-main">Terbium</span> Chemical element, symbol Tb and atomic number 65

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<span class="mw-page-title-main">Mischmetal</span> Pyrophoric rare-earth metal alloy

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<span class="mw-page-title-main">Thorium dioxide</span> Chemical compound

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<span class="mw-page-title-main">Didymium</span> Mixture of praseodymium and neodymium

Didymium is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially with a gas (propane)-powered forge, where it provides a filter that selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass without having a detrimental effect on general vision, unlike dark welder's glasses. The usefulness of didymium glass for eye protection of this sort was discovered by Sir William Crookes.

<span class="mw-page-title-main">Praseodymium(III) chloride</span> Chemical compound

Praseodymium(III) chloride is the inorganic compound with the formula PrCl3. Like other lanthanide trichlorides, it exists both in the anhydrous and hydrated forms. It is a blue-green solid that rapidly absorbs water on exposure to moist air to form a light green heptahydrate.

<span class="mw-page-title-main">Yttrium</span> Chemical element, symbol Y and atomic number 39

Yttrium is a chemical element; it has symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals and is never found in nature as a free element. 89Y is the only stable isotope and the only isotope found in the Earth's crust.

<span class="mw-page-title-main">Cerium</span> Chemical element, symbol Ce and atomic number 58

Cerium is a chemical element; it has symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the oxidation state of +3 characteristic of the series, it also has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no known biological role in humans but is not particularly toxic, except with intense or continued exposure.

<span class="mw-page-title-main">Thorium compounds</span> Chemical compounds

Many compounds of thorium are known: this is because thorium and uranium are the most stable and accessible actinides and are the only actinides that can be studied safely and legally in bulk in a normal laboratory. As such, they have the best-known chemistry of the actinides, along with that of plutonium, as the self-heating and radiation from them is not enough to cause radiolysis of chemical bonds as it is for the other actinides. While the later actinides from americium onwards are predominantly trivalent and behave more similarly to the corresponding lanthanides, as one would expect from periodic trends, the early actinides up to plutonium have relativistically destabilised and hence delocalised 5f and 6d electrons that participate in chemistry in a similar way to the early transition metals of group 3 through 8: thus, all their valence electrons can participate in chemical reactions, although this is not common for neptunium and plutonium.

<span class="mw-page-title-main">Neodymium compounds</span> Chemical compounds with at least one neodymium atom

Neodymium compounds are compounds formed by the lanthanide metal neodymium (Nd). In these compounds, neodymium generally exhibits the +3 oxidation state, such as NdCl3, Nd2(SO4)3 and Nd(CH3COO)3. Compounds with neodymium in the +2 oxidation state are also known, such as NdCl2 and NdI2. Some neodymium compounds have colors that vary based upon the type of lighting.

Praseodymium compounds are compounds formed by the lanthanide metal praseodymium (Pr). In these compounds, praseodymium generally exhibits the +3 oxidation state, such as PrCl3, Pr(NO3)3 and Pr(CH3COO)3. However, compounds with praseodymium in the +2 and +4 oxidation states, and unlike other lanthanides, the +5 oxidation state, are also known.

Cerium compounds are compounds containing the element cerium (Ce), a lanthanide. Cerium exists in two main oxidation states, Ce(III) and Ce(IV). This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidizing agents peroxodisulfate or bismuthate. The value of E(Ce4+/Ce3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state.


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Further reading