Praseodymium compounds are compounds formed by the
lanthanide
The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...
metal
praseodymium
Praseodymium is a chemical element with the Symbol (chemistry), symbol Pr and the atomic number 59. It is the third member of the lanthanide series and is considered to be one of the rare-earth metals. It is a soft, silvery, malleable and ductile ...
(Pr). In these compounds, praseodymium generally exhibits the +3
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
, such as PrCl
3, Pr(NO
3)
3 and Pr(CH
3COO)
3. However, compounds with praseodymium in the +2 and +4 oxidation states, and unlike other
lanthanide
The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...
s, the +5 oxidation state, are also known.
Oxides
Praseodymium can form
oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
s in many different ways, although the only oxides that are stable at room temperature are
Pr2O3,
Pr6O11 and
PrO2. Praseodymium(III) oxide is a green powder that forms hexagonal crystals,
and crystallizes in the
manganese(III) oxide
Manganese(III) oxide is a chemical compound with the formula Mn2O3. It occurs in nature as the mineral bixbyite (recently changed to bixbyite-(Mn)IMA 21-H: Redefinition of bixbyite and definition of bixbyite-(Fe) and bixbyite-(Mn). CNMNC Newslette ...
or
bixbyite
Bixbyite is a manganese iron oxide mineral with chemical formula: (Mn,Fe)2O3. The iron/manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 - 6.5. It is a somewhat rare ...
structure.
Praseodymium(IV) oxide can be produced by boiling
Pr6O11 in water or
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
:
[ zh, 《无机化学丛书》.第七卷 钪 稀土元素. 科学出版社. 1.3.4 氧化态+4的化合物., translation=Inorganic Chemistry Series. Volume VII Rare Earth Elements. Science Press. 1.3.4 Compounds with oxidation state +4. P193~195]
: Pr
6O
11 + 3 H
2O → 4 PrO
2 + 2 Pr(OH)
3
Praseodymium(III,IV) oxide is the most stable form of the praseodymium oxides at
ambient temperature and pressure.
It is soluble in water and has a
cubic fluorite structure In solid state chemistry, the fluorite structure refers to a common motif for compounds with the formula MX2. The X ions occupy the eight tetrahedral interstitial sites whereas M ions occupy the regular sites of a face-centered cubic (FCC) structure ...
.
It can be prepared via solid-state methods such as thermolysis, molten salt method,
calcination
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), genera ...
or
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
.
[Shamshi Hassan, M., Shaheer Akhtar, M., Shim, KB. et al. Morphological and Electrochemical Properties of Crystalline Praseodymium Oxide Nanorods. Nanoscale Res Lett 5, 735 (2010). https://doi.org/10.1007/s11671-010-9547-8]
In addition to Pr
6O
11, praseodymium also forms a system of oxides at different phases:
Halides
Praseodymium metal reacts with all the stable
halogen
The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
s to form green trihalides:
:2 Pr (s) + 3 F
2 (g) → 2 PrF
3 (s)
:2 Pr (s) + 3 Cl
2 (g) → 2 PrCl
3 (s)
:2 Pr (s) + 3 Br
2 (g) → 2 PrBr
3 (s)
:2 Pr (s) + 3 I
2 (g) → 2 PrI
3 (s)
Praseodymium(III) fluoride is the most stable fluoride of praseodymium. It can be prepared the reaction between
praseodymium(III) nitrate and
sodium fluoride
Sodium fluoride (NaF) is an inorganic compound with the formula . It is used in trace amounts in the fluoridation of drinking water, in toothpaste, in metallurgy, and as a flux. It is a colorless or white solid that is readily soluble in water. I ...
will produce praseodymium(III) fluoride as a green crystalline solid.
Praseodymium(III) chloride is a light green solid that can be prepared by treating praseodymium metal with
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
. It is usually purified by vacuum sublimation.
It is
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
ic, classified as "hard" according to the
HSAB concept
HSAB concept is a jargon for "hard and soft (Lewis) acids and bases". HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways. It assigns the terms 'hard' or 'soft', and 'acid' or 'base' to chemic ...
. Rapid heating of the
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
may cause small amounts of
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
.
[F. T. Edelmann, P. Poremba, in: ''Synthetic Methods of Organometallic and Inorganic Chemistry'', (W. A. Herrmann, ed.), Vol. 6, Georg Thieme Verlag, Stuttgart, 1997.] PrCl
3 forms a stable Lewis acid-base complex K
2PrCl
5 by reaction with
potassium chloride
Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt ...
; this compound shows interesting
optical
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
and
magnetic
Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...
properties.
Praseodymium(III) bromide is the only stable bromide of praseodymium. It adopts the
crystal structure.
The praseodymium ions are 9-coordinate and adopt a
tricapped trigonal prismatic geometry.
The praseodymium–bromine bond lengths are 3.05 Å and 3.13 Å.
Praseodymium(III) iodide can be prepared by heating praseodymium and
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
in an inert atmosphere produces praseodymium(III) iodide,
or by heating praseodymium with mercury(II) iodide.
It forms
orthorhombic crystals which are
hygroscopic
Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...
.
It crystallizes in the
PuBr3 type
with space group ''Cmcm'' (No. 63) with ''a'' = 4.3281(6) Å, ''b'' = 14.003(6) Å and ''c'' = 9.988(3) Å.
The
tetrafluoride, PrF4, is also known, and is produced by reacting a mixture of
sodium fluoride
Sodium fluoride (NaF) is an inorganic compound with the formula . It is used in trace amounts in the fluoridation of drinking water, in toothpaste, in metallurgy, and as a flux. It is a colorless or white solid that is readily soluble in water. I ...
and
praseodymium(III) fluoride with
fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
gas, producing Na
2PrF
6, following which sodium fluoride is removed from the reaction mixture with liquid
hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock i ...
.
[Greenwood and Earnshaw, p. 1240–2] Additionally, praseodymium forms a bronze
diiodide; like the diiodides of lanthanum, cerium, and
gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen ...
, it is a praseodymium(III)
electride
An electride is an ionic compound in which an electron is the anion. Solutions of alkali metals in ammonia are electride salts. In the case of sodium, these blue solutions consist of a(NH3)6sup>+ and solvated electrons:
:Na + 6 NH3 → ...
compound.
Organopraseodymium compounds
Organopraseodymium compounds are compounds with a
praseodymium
Praseodymium is a chemical element with the Symbol (chemistry), symbol Pr and the atomic number 59. It is the third member of the lanthanide series and is considered to be one of the rare-earth metals. It is a soft, silvery, malleable and ductile ...
-to-
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
bond. These compounds are very similar to
those of the other lanthanides, as they all share an inability to undergo
π backbonding
In chemistry, π backbonding, also called π backdonation, is when electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a ''π-acceptor ligand''. It is especially common in the organometallic che ...
. They are thus mostly restricted to the mostly ionic
cyclopentadienide
In chemistry, the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of and abbreviated as Cp−. It is formed from the deprotonation of the molecule cyclopentadiene.
Properties
The cyclopentadienyl anion i ...
s (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.
The coordination chemistry of praseodymium is largely that of the large, electropositive Pr
3+ ion, and is thus largely similar to those of the other early lanthanides La
3+, Ce
3+, and Nd
3+. For instance, like lanthanum, cerium, and neodymium,
praseodymium nitrate forms both the 4:3 and 1:1 complexes with
18-crown-6
18-Crown-6 is an organic compound with the formula 2H4O and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a li ...
, whereas the middle lanthanides from
promethium
Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of onl ...
to
gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen ...
can only form the 4:3 complex and the later lanthanides from
terbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with wa ...
to
lutetium
Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted am ...
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
3">r3 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.
However, the first example of a molecular complex of praseodymium(IV) has recently been reported. Like the other organolanthanide compounds, properties of organopraseodymium compounds include:
*Organopraseodymium compounds are very air- and water-sensitive and
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...
.
*Chemistry in the 0
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
is far more limited. In fact, their electropositive nature makes their organometallic compounds more likely to be ionic.
*Organopraseodymium compounds form no stable
carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...
s at room temperature; organopraseodymium carbonyl compounds have been observed only in
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
matrices, and decompose when heated to 40
K.
σ-Bonded complexes
Metal-carbon σ bonds are found in alkyls of praeodymium such as
6">rMe6sup>3− and Pr
3)2">H(SiMe3)2sub>3.
π-Bonded complexes
Cyclopentadienyl complex
A cyclopentadienyl complex is a coordination complex of a metal and cyclopentadienyl groups (, abbreviated as Cp−). Cyclopentadienyl ligands almost invariably bind to metals as a pentahapto (''η''5-) bonding mode. The metal–cyclopentadien ...
es, are known for praseodymium. It can be produced by the following reaction scheme:
:3 Na
p+ PrCl
3 → Pr
psub>3 + 3 NaCl
These compounds are of limited use and academic interest.
Applications
Praseodymium(III) nitride is used in high-end electric and semiconductor products, and as a raw material to produce phosphor. Also it is used as a magnetic material and sputtering target material. Many praseodymium compounds, such as
praseodymium(III) oxalate, are used to colour some glasses and enamels. If mixed with certain other materials, praseodymium(III) oxalate paints glass intense yellow.
Praseodymium(III,IV) oxide has a number of potential applications in chemical
catalysis
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, and is often used in conjunction with a promoter such as
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
or
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
to improve its catalytic performance. It has a high-K dielectric constant of around 30 and very low leakage currents
[Osten HJ, Liu JP, P Gaworzewski, E Bugiel, Zaumseil P: IEDM Technical Digest 653. 2000.] which have also made it a promising material for many potential applications in
nanodevice
A molecular machine, nanite, or nanomachine is a molecular component that produces quasi-mechanical movements (output) in response to specific stimuli (input). In cellular biology, macromolecular machines frequently perform tasks essential for ...
s and
microelectronic
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre-sc ...
s.
[Shamshi Hassan, M., Shaheer Akhtar, M., Shim, KB. et al. Morphological and Electrochemical Properties of Crystalline Praseodymium Oxide Nanorods. Nanoscale Res Lett 5, 735 (2010). https://doi.org/10.1007/s11671-010-9547-8]
References
See also
*
Neodymium compounds
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 stat ...
*
Europium compounds
{{Chemical compounds by element
*
Chemical compounds by element