Strontium carbide

Strontium carbide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.925 Edit this at Wikidata
  • InChI=1S/C2.Sr/c1-2;/q-2;+2
    Key: QBIPZSRMYKVEBD-UHFFFAOYSA-N
  • [Sr+2].[C-]#[C-]
Properties
C2Sr
Molar mass 111.64 g·mol−1
Related compounds
Other cations
 Calcium carbide; Barium carbide; Europium carbide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Strontium carbide (also more precisely known as strontium acetylide or strontium dicarbide) is a salt with chemical formula SrC2. It was first synthesized by Moissan in 1894.[1]

Strontium carbide can be formed in an electric arc furnace from strontium carbonate and a reductant, such as a reducing sugar[1][2] or magnesium metal.[3] Alternatively, carbothermal reduction of strontium oxide with graphite begins around 150 °C and is catalyzed by calcium oxide.[4] Classical organic chemistry syntheses include transmetallation from mercury acetylide or an acid-base reaction between dibenzylstrontium and acetylene, although these techniques often produce complexes with the solvent.[5] Direct formation from the elements has a notional enthalpy of -20 kcal/mol.[6]

Nevertheless, strontium carbide may be only metastable when encapsulated in a fullerene.[7] It slowly hydrolyzes in air to acetylene.[1]

The material is polymorphic, forming a monoclinic crystal structure akin to calcium carbide II[2] and a black[1] tetragonal phase. Heated to 370 °C, it reversibly converts to a face-centered cubic (fcc) lattice.[2] Yttrium carbide retains the fcc lattice down to room temperature; the difference is a 3eg orbital that strontium lacks the electrons to fill.[8] Cyanamide impurities stabilize one other strontium carbide polymorph, just as they do for calcium carbide. The stabilized calcium carbide polymorph is triclinic, and the strontium carbide polymorph is believed to be so as well.[9]

At roughly 1800 °C, strontium carbide melts.[6] It forms a solid solution with europium carbide, as Eu2+ has an almost identical ionic radius to Sr2+.[10]

Strontium carbide is a chemical intermediate in an archaic carbon-14 dating technique: burning the material to be dated releases carbon dioxide, trapped as strontium carbonate. Magnesium then reduces the carbonate to strontium carbide and hydrolysis releases acetylene.[3][11] The radioactive decay of the acetylene can then be observed directly[11] or heating to 600 °C polymerizes the acetylene to benzene for a liquid scintillator.[3]

Solid state metathesis of strontium carbide and a (complex) metal oxide gives the corresponding metal carbide and strontium oxide. The latter washes away easily in pure water.[12]

  1. ^ a b c d Cite error: The named reference hist was invoked but never defined (see the help page).
  2. ^ a b c Cite error: The named reference poly was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference C14 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference gas was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference orgo was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference VP was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference fuller was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference eg was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference CaPoly was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference ss was invoked but never defined (see the help page).
  11. ^ a b Cite error: The named reference Osaka was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference SSM was invoked but never defined (see the help page).