Samarium 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
samarium (Sm). In these compounds, samarium generally exhibits the +3 oxidation state, such as
SmCl3,
Sm(NO3)3 and
Sm(C2O4)3. Compounds with samarium in the +2 oxidation state are also known, for example
SmI2.
Properties of samarium compounds
Chalcogenides
Oxides
The most stable
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 ...
of samarium is the
sesquioxide
A sesquioxide is an oxide of an element (or radical), where the ratio between the number of atoms of that element and the number of atoms of oxygen is 2:3. For example, aluminium oxide and phosphorus(III) oxide are sesquioxides.
Many sesquioxid ...
Sm
2O
3. Like many samarium compounds, it exists in several crystalline phases. The
trigonal form is obtained by slow cooling from the melt. The
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...
of Sm
2O
3 is high (2345 °C), so it is usually melted not by direct heating, but with
induction heating, through a radio-frequency coil. Sm
2O
3 crystals of
monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...
symmetry can be grown by the flame fusion method (
Verneuil process
The Verneuil method (or Verneuil process or Verneuil technique), also called flame fusion, was the first commercially successful method of manufacturing synthetic gemstones, developed in the late 1883 by the French chemist Auguste Verneuil. It ...
) from Sm
2O
3 powder, that yields cylindrical boules up to several centimeters long and about one centimeter in diameter. The boules are transparent when pure and defect-free and are orange otherwise. Heating the metastable trigonal Sm
2O
3 to 1900 °C converts it to the more stable monoclinic phase.
Cubic Sm
2O
3 has also been described.
Samarium is one of the few lanthanides that form a monoxide, SmO. This lustrous golden-yellow compound was obtained by reducing Sm
2O
3 with samarium metal at high temperature (1000 °C) and pressure above 50 kbar; lowering the pressure resulted in incomplete reaction. SmO has cubic rock-salt lattice structure.
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C ...
, p. 1239
Other chalcogenides
Samarium forms a trivalent
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
,
selenide and
telluride. Divalent chalcogenides
SmS
Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...
,
SmSe and
SmTe with cubic rock-salt
crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...
are also known. They are remarkable by converting from semiconducting to metallic state at room temperature upon application of pressure. Whereas the transition is continuous and occurs at about 20–30 kbar in SmSe and SmTe, it is abrupt in SmS and requires only 6.5 kbar. This effect results in spectacular color change in SmS from black to golden yellow when its crystals of films are scratched or polished. The transition does not change lattice symmetry, but there is a sharp decrease (~15%) in the crystal volume.
[Beaurepaire, Eric (Ed.]
''Magnetism: a synchrotron radiation approach''
Springer, 2006 p. 393 It shows
hysteresis
Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
, that is when the pressure is released, SmS returns to the semiconducting state at much lower pressure of about 0.4 kbar.
Halides
Samarium metal reacts with all the
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, forming tri
halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluor ...
s:
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C ...
, pp. 1236, 1241
:2 Sm (s) + 3 X
2 (g) → 2 SmX
3 (s) (X = F, Cl, Br or I)
Their further reduction with samarium, lithium or sodium metals at elevated temperatures (about 700–900 °C) yields dihalides.
The diiodide can also be prepared by heating SmI
3, or by reacting the metal with
1,2-diiodoethane
1,2-Diiodoethane is an organoiodine compound.
Preparation and reactions
1,2-Diiodoethane can be prepared by the reaction of ethylene with iodine (I):
:CH + I CHI
1,2-Diiodoethane is most commonly used in organic synthesis in the preparation ...
in anhydrous
tetrahydrofuran
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...
at room temperature:
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C ...
, p. 1240
:Sm (s) + ICH
2-CH
2I → SmI
2 + CH
2=CH
2.
In addition to dihalides, the reduction also produces many
non-stoichiometric
In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...
samarium halides with a well-defined crystal structure, such as Sm
3F
7, Sm
14F
33, Sm
27F
64,
Sm
11Br
24, Sm
5Br
11 and Sm
6Br
13.
As reflected in the table above, samarium halides change their crystal structures when one type of halide atom is substituted for another, which is an uncommon behavior for most elements (e.g. actinides). Many halides have two major crystal phases for one composition, one being significantly more stable and another being metastable. The latter is formed upon compression or heating, followed by quenching to ambient conditions. For example, compressing the usual monoclinic samarium diiodide and releasing the pressure results in a PbCl
2-type orthorhombic structure (density 5.90 g/cm
3), and similar treatment results in a new phase of samarium triiodide (density 5.97 g/cm
3).
Borides
Sintering
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
powders of samarium oxide and boron, in vacuum, yields a powder containing several samarium boride phases, and their volume ratio can be controlled through the mixing proportion.
The powder can be converted into larger crystals of a certain samarium boride using
arc melting
An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc.
Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to a ...
or
zone melting
Zone melting (or zone refining, or floating-zone method, or floating-zone technique) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molte ...
techniques, relying on the different melting/crystallization temperature of SmB
6 (2580 °C), SmB
4 (about 2300 °C) and SmB
66 (2150 °C). All these materials are hard, brittle, dark-gray solids with the hardness increasing with the boron content.
Samarium diboride is too volatile to be produced with these methods and requires high pressure (about 65 kbar) and low temperatures between 1140 and 1240 °C to stabilize its growth. Increasing the temperature results in the preferential formations of SmB
6.
Samarium hexaboride
Samarium hexaboride is a typical intermediate-valence compound where samarium is present both as Sm
2+ and Sm
3+ ions at the ratio 3:7.
It belongs to a class of
Kondo insulators, that is at high temperatures (above 50 K), its properties are typical of a Kondo metal, with metallic electrical conductivity characterized by strong electron scattering, whereas at low temperatures, it behaves as a non-magnetic insulator with a narrow
band gap of about 4–14 meV. The cooling-induced metal-insulator transition in SmB
6 is accompanied by a sharp increase in the
thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
, peaking at about 15 K. The reason for this increase is that electrons themselves do not contribute to the thermal conductivity at low temperatures, which is dominated by
phonon
In physics, a phonon is a collective excitation in a periodic, Elasticity (physics), elastic arrangement of atoms or molecules in condensed matter physics, condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phon ...
s, but the decrease in electron concentration reduced the rate of electron-phonon scattering.
New research seems to show that it may be a
topological insulator.
Other inorganic compounds
Samarium
carbide
In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.
Interstitial / Metallic carbides
The carbides of the ...
s are prepared by melting a graphite-metal mixture in an inert atmosphere. After the synthesis, they are unstable in air and are studied also under inert atmosphere.
Samarium monophosphide SmP is a
semiconductor
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
with the bandgap of 1.10 eV, the same as in
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
, and high electrical conductivity of
n-type. It can be prepared by annealing at 1100 °C an evacuated quartz ampoule containing mixed powders of phosphorus and samarium. Phosphorus is highly volatile at high temperatures and may explode, thus the heating rate has to be kept well below 1 °C/min.
Similar procedure is adopted for the monarsenide
SmAs, but the synthesis temperature is higher at 1800 °C.
Numerous crystalline binary compounds are known for samarium and one of the group-14, 15 or 16 element X, where X is Si, Ge, Sn, Pb, Sb or Te, and metallic alloys of samarium form another large group. They are all prepared by annealing mixed powders of the corresponding elements. Many of the resulting compounds are non-stoichiometric and have nominal compositions Sm
aX
b, where the b/a ratio varies between 0.5 and 3.
Organosamarium compounds
Samarium forms a
cyclopentadienide and its chloroderivatives and . They are prepared by reacting samarium trichloride with in
tetrahydrofuran
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...
. Contrary to cyclopentadienides of most other lanthanides, in some rings bridge each other by forming ring vertexes η
1 or edges η
2 toward another neighboring samarium, thus creating polymeric chains.
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C ...
, p. 1248 The chloroderivative has a dimer structure, which is more accurately expressed as . There, the chlorine bridges can be replaced, for instance, by iodine, hydrogen or nitrogen atoms or by CN groups.
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, p. 1249
The ()
− ion in samarium cyclopentadienides can be replaced by the indenide ()
− or
cyclooctatetraenide ()
2− ring, resulting in or . The latter compound has a structure similar to
uranocene. There is also a cyclopentadienide of divalent samarium,
2− a solid that sublimates at about 85 °C. Contrary to
ferrocene
Ferrocene is an organometallic compound with the formula . The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, a ...
, the rings in are not parallel but are tilted by 40°.
A
metathesis reaction in tetrahydrofuran or
ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...
gives
alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...
s and
aryl
In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used as ...
s of samarium:
:
:
Here R is a hydrocarbon group and Me =
methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...
.
See also
*
:Samarium compounds
*
:Chemical compounds by element
*
Praseodymium compounds
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 ...
*
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
Europium compounds are compounds formed by the lanthanide metal europium (Eu). In these compounds, europium generally exhibits the +3 oxidation state, such as EuCl3, Eu(NO3)3 and Eu(CH3COO)3. Compounds with europium in the +2 oxidation state are ...
References
{{Chemical compounds by element
Chemical compounds by element
Samarium compounds