Samarium compounds
Samarium compounds are compounds formed by the lanthanide 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
Formula | color | symmetry | space group | No | Pearson symbol | a (pm) | b (pm) | c (pm) | Z | density, g/cm3 |
---|---|---|---|---|---|---|---|---|---|---|
Sm | silvery | trigonal[1] | R3m | 166 | hR9 | 362.9 | 362.9 | 2621.3 | 9 | 7.52 |
Sm | silvery | hexagonal[1] | P63/mmc | 194 | hP4 | 362 | 362 | 1168 | 4 | 7.54 |
Sm | silvery | tetragonal[2] | I4/mmm | 139 | tI2 | 240.2 | 240.2 | 423.1 | 2 | 20.46 |
SmO | golden | cubic[3] | Fm3m | 225 | cF8 | 494.3 | 494.3 | 494.3 | 4 | 9.15 |
Sm2O3 | trigonal[4] | P3m1 | 164 | hP5 | 377.8 | 377.8 | 594 | 1 | 7.89 | |
Sm2O3 | monoclinic[4] | C2/m | 12 | mS30 | 1418 | 362.4 | 885.5 | 6 | 7.76 | |
Sm2O3 | cubic[5] | Ia3 | 206 | cI80 | 1093 | 1093 | 1093 | 16 | 7.1 | |
SmH2 | cubic[6] | Fm3m | 225 | cF12 | 537.73 | 537.73 | 537.73 | 4 | 6.51 | |
SmH3 | hexagonal[7] | P3c1 | 165 | hP24 | 377.1 | 377.1 | 667.2 | 6 | ||
Sm2B5 | gray | monoclinic[8] | P21/c | 14 | mP28 | 717.9 | 718 | 720.5 | 4 | 6.49 |
SmB2 | hexagonal[9] | P6/mmm | 191 | hP3 | 331 | 331 | 401.9 | 1 | 7.49 | |
SmB4 | tetragonal[10] | P4/mbm | 127 | tP20 | 717.9 | 717.9 | 406.7 | 4 | 6.14 | |
SmB6 | cubic[11] | Pm3m | 221 | cP7 | 413.4 | 413.4 | 413.4 | 1 | 5.06 | |
SmB66 | cubic[12] | Fm3c | 226 | cF1936 | 2348.7 | 2348.7 | 2348.7 | 24 | 2.66 | |
Sm2C3 | cubic[13] | I43d | 220 | cI40 | 839.89 | 839.89 | 839.89 | 8 | 7.55 | |
SmC2 | tetragonal[13] | I4/mmm | 139 | tI6 | 377 | 377 | 633.1 | 2 | 6.44 | |
SmF2 | purple[14] | cubic[15] | Fm3m | 225 | cF12 | 587.1 | 587.1 | 587.1 | 4 | 6.18 |
SmF3 | white[14] | orthorhombic[15] | Pnma | 62 | oP16 | 667.22 | 705.85 | 440.43 | 4 | 6.64 |
SmCl2 | brown[14] | orthorhombic[16] | Pnma | 62 | oP12 | 756.28 | 450.77 | 901.09 | 4 | 4.79 |
SmCl3 | yellow[14] | hexagonal[15] | P63/m | 176 | hP8 | 737.33 | 737.33 | 416.84 | 2 | 4.35 |
SmBr2 | brown[14] | orthorhombic[17] | Pnma | 62 | oP12 | 797.7 | 475.4 | 950.6 | 4 | 5.72 |
SmBr3 | yellow[14] | orthorhombic[18] | Cmcm | 63 | oS16 | 404 | 1265 | 908 | 2 | 5.58 |
SmI2 | green[14] | monoclinic | P21/c | 14 | mP12 | |||||
SmI3 | orange[14] | trigonal[19] | R3 | 63 | hR24 | 749 | 749 | 2080 | 6 | 5.24 |
SmN | cubic[20] | Fm3m | 225 | cF8 | 357 | 357 | 357 | 4 | 8.48 | |
SmP | cubic[21] | Fm3m | 225 | cF8 | 576 | 576 | 576 | 4 | 6.3 | |
SmAs | cubic[22] | Fm3m | 225 | cF8 | 591.5 | 591.5 | 591.5 | 4 | 7.23 |
Chalcogenides
Oxides
The most stable
Samarium is one of the few lanthanides that form a monoxide, SmO. This lustrous golden-yellow compound was obtained by reducing Sm2O3 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.[3][23]
Other chalcogenides
Samarium forms a trivalent
Halides
Samarium metal reacts with all the halogens, forming trihalides:[27]
- 2 Sm (s) + 3 X2 (g) → 2 SmX3 (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.[16] The diiodide can also be prepared by heating SmI3, or by reacting the metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room temperature:[28]
- Sm (s) + ICH2-CH2I → SmI2 + CH2=CH2.
In addition to dihalides, the reduction also produces many non-stoichiometric samarium halides with a well-defined crystal structure, such as Sm3F7, Sm14F33, Sm27F64,[15] Sm11Br24, Sm5Br11 and Sm6Br13.[29]
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 PbCl2-type orthorhombic structure (density 5.90 g/cm3),[30] and similar treatment results in a new phase of samarium triiodide (density 5.97 g/cm3).[31]
Borides
Sintering 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.[32] The powder can be converted into larger crystals of a certain samarium boride using arc melting or zone melting techniques, relying on the different melting/crystallization temperature of SmB6 (2580 °C), SmB4 (about 2300 °C) and SmB66 (2150 °C). All these materials are hard, brittle, dark-gray solids with the hardness increasing with the boron content.[11] 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 SmB6.[9]
Samarium hexaboride
Samarium hexaboride is a typical intermediate-valence compound where samarium is present both as Sm2+ and Sm3+ ions at the ratio 3:7.
New research seems to show that it may be a topological insulator.[35][36][37]
Other inorganic compounds
Samarium
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 SmaXb, where the b/a ratio varies between 0.5 and 3.[38][39][40]
Organosamarium compounds
Samarium forms a cyclopentadienide Sm(C5H5)3 and its chloroderivatives Sm(C5H5)2Cl and Sm(C5H5)Cl2. They are prepared by reacting samarium trichloride with NaC5H5 in tetrahydrofuran. Contrary to cyclopentadienides of most other lanthanides, in Sm(C5H5)3 some C5H5 rings bridge each other by forming ring vertexes η1 or edges η2 toward another neighboring samarium, thus creating polymeric chains.[41] The chloroderivative Sm(C5H5)2Cl has a dimer structure, which is more accurately expressed as (η(5)−C5H5)2Sm(−Cl)2(η(5)−C5H5)2. There, the chlorine bridges can be replaced, for instance, by iodine, hydrogen or nitrogen atoms or by CN groups.[42]
The (C5H5)− ion in samarium cyclopentadienides can be replaced by the indenide (C9H7)− or cyclooctatetraenide (C8H8)2− ring, resulting in Sm(C9H7)3 or KSm(η(8)−C8H8)2. The latter compound has a structure similar to uranocene. There is also a cyclopentadienide of divalent samarium, Sm(C5H5)2− a solid that sublimates at about 85 °C. Contrary to ferrocene, the C5H5 rings in Sm(C5H5)2 are not parallel but are tilted by 40°.[42][43]
A
- SmCl3 + 3LiR → SmR3 + 3LiCl
- Sm(OR)3 + 3LiCH(SiMe3)2 → Sm{CH(SiMe3)2}3 + 3LiOR
Here R is a hydrocarbon group and Me =
Pictures of samarium compounds
See also
- Category:Samarium compounds
- Category:Chemical compounds by element
- Praseodymium compounds
- Neodymium compounds
- Europium compounds
References
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