Carbide: Difference between revisions
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imported>Bernanke's Crossbow →Allylides: New src |
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The long-held view is that the carbon atoms fit into octahedral interstices in a close-packed metal lattice when the metal atom radius is greater than approximately 135 pm:<ref name="Greenwood" /> | The long-held view is that the carbon atoms fit into octahedral interstices in a close-packed metal lattice when the metal atom radius is greater than approximately 135 pm:<ref name="Greenwood" /> | ||
*When the metal atoms are [[close-packing|cubic close-packed]], (ccp), then filling all of the octahedral interstices with carbon achieves 1:1 stoichiometry with the [[Rock-salt structure|rock salt structure]].<ref name=Zhu>{{Cite journal |last1=Zhu |first1=Qinqing |last2=Xiao |first2=Guorui |last3=Cui |first3=Yanwei |last4=Yang |first4=Wuzhang |last5=Wu |first5=Siqi |last6=Cao |first6=Guang-Han |last7=Ren |first7=Zhi |date=2021-10-15 |title=Anisotropic lattice expansion and enhancement of superconductivity induced by interstitial carbon doping in Rhenium |url=https://www.sciencedirect.com/science/article/pii/S0925838821016996 |journal=Journal of Alloys and Compounds |language=en |volume=878 | | *When the metal atoms are [[close-packing|cubic close-packed]], (ccp), then filling all of the octahedral interstices with carbon achieves 1:1 stoichiometry with the [[Rock-salt structure|rock salt structure]].<ref name=Zhu>{{Cite journal |last1=Zhu |first1=Qinqing |last2=Xiao |first2=Guorui |last3=Cui |first3=Yanwei |last4=Yang |first4=Wuzhang |last5=Wu |first5=Siqi |last6=Cao |first6=Guang-Han |last7=Ren |first7=Zhi |date=2021-10-15 |title=Anisotropic lattice expansion and enhancement of superconductivity induced by interstitial carbon doping in Rhenium |url=https://www.sciencedirect.com/science/article/pii/S0925838821016996 |journal=Journal of Alloys and Compounds |language=en |volume=878 |article-number=160290 |doi=10.1016/j.jallcom.2021.160290 |issn=0925-8388|url-access=subscription }}</ref> | ||
*When the metal atoms are [[close-packing|hexagonal close-packed]], (hcp), as the octahedral interstices lie directly opposite each other on either side of the layer of metal atoms, filling only one of these with carbon achieves 2:1 stoichiometry with the CdI<sub>2</sub> structure.<ref name=Zhu/> | *When the metal atoms are [[close-packing|hexagonal close-packed]], (hcp), as the octahedral interstices lie directly opposite each other on either side of the layer of metal atoms, filling only one of these with carbon achieves 2:1 stoichiometry with the CdI<sub>2</sub> structure.<ref name=Zhu/> | ||
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====Methanides==== | ====Methanides==== | ||
Methanides are a subset of carbides distinguished by their tendency to decompose in water producing [[methane]]. Three examples are [[aluminium carbide]] {{chem2|Al4C3}}, [[magnesium carbide]] {{chem2|Mg2C}}<ref>{{cite journal|title=Synthesis of Mg2C: A Magnesium Methanide|author1=O.O. Kurakevych |author2=T.A. Strobel |author3=D.Y. Kim |author4=G.D. Cody |volume =52|issue=34|year=2013|pages=8930–8933|journal=Angewandte Chemie International Edition|doi=10.1002/anie.201303463|pmid = 23824698}}</ref> and [[beryllium carbide]] {{chem2|Be2C}}. | Methanides are a subset of carbides distinguished by their tendency to decompose in water producing [[methane]]. Three examples are [[aluminium carbide]] {{chem2|Al4C3}}, [[magnesium carbide]] {{chem2|Mg2C}}<ref>{{cite journal|title=Synthesis of Mg2C: A Magnesium Methanide|author1=O.O. Kurakevych |author2=T.A. Strobel |author3=D.Y. Kim |author4=G.D. Cody |volume =52|issue=34|year=2013|pages=8930–8933|journal=Angewandte Chemie International Edition|doi=10.1002/anie.201303463|pmid = 23824698 |bibcode=2013ACIE...52.8930K }}</ref> and [[beryllium carbide]] {{chem2|Be2C}}. | ||
Transition metal carbides are not saline: their reaction with water is very slow and is usually neglected. For example, depending on surface porosity, 5–30 atomic layers of [[titanium carbide]] are hydrolyzed, forming [[methane]] within 5 minutes at ambient conditions, following by saturation of the reaction.<ref>{{cite journal|url=https://link.springer.com/article/10.1007%2FBF00780135|title=Reaction of titanium carbide with water|author1=A. I. Avgustinik |author2=G. V. Drozdetskaya |author3=S. S. Ordan'yan |volume =6|issue=6|year=1967|pages=470–473|journal=Powder Metallurgy and Metal Ceramics|doi=10.1007/BF00780135|s2cid=134209836|url-access=subscription}}</ref> | Transition metal carbides are not saline: their reaction with water is very slow and is usually neglected. For example, depending on surface porosity, 5–30 atomic layers of [[titanium carbide]] are hydrolyzed, forming [[methane]] within 5 minutes at ambient conditions, following by saturation of the reaction.<ref>{{cite journal|url=https://link.springer.com/article/10.1007%2FBF00780135|title=Reaction of titanium carbide with water|author1=A. I. Avgustinik |author2=G. V. Drozdetskaya |author3=S. S. Ordan'yan |volume =6|issue=6|year=1967|pages=470–473|journal=Powder Metallurgy and Metal Ceramics|doi=10.1007/BF00780135|s2cid=134209836|url-access=subscription}}</ref> | ||
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====Allylides==== | ====Allylides==== | ||
The [[polyatomic ion]] {{chem2|C3(4−)}}, sometimes called '''allylide''', is found in {{chem2|Li4C3}} and {{chem2|Mg2C3}}. The ion is linear and is [[isoelectronic]] with {{CO2}}.<ref name="Greenwood" /> The C–C distance in {{chem2|Mg2C3}} is 133.2 pm.<ref>{{cite journal|title=Crystal Structure of Magnesium Sesquicarbide|doi=10.1021/ic00041a018|author1=Fjellvag H. |author2=Pavel K. |journal=Inorg. Chem. |year=1992|volume=31|page=3260|issue=15}}</ref> {{chem2|Mg2C3}} yields [[methylacetylene]], {{chem2|CH3CCH}}, and [[propadiene]], {{chem2|CH2CCH2}} | The [[polyatomic ion]] {{chem2|C3(4−)}}, sometimes called '''allylide''', is found in {{chem2|Li4C3}} and {{chem2|Mg2C3}}. The ion is linear and is [[isoelectronic]] with {{CO2}}.<ref name="Greenwood" /> The C–C distance in {{chem2|Mg2C3}} is 133.2 pm.<ref>{{cite journal|title=Crystal Structure of Magnesium Sesquicarbide|doi=10.1021/ic00041a018|author1=Fjellvag H. |author2=Pavel K. |journal=Inorg. Chem. |year=1992|volume=31|page=3260|issue=15}}</ref> | ||
{{chem2|Mg2C3}} hydrolysis yields [[methylacetylene]], {{chem2|CH3CCH}}, and [[propadiene]], {{chem2|CH2CCH2}}, which was the first indication that the salt contains {{chem2|C3(4−)}}. Conversely, {{chem2|Li4C3}} is made from the reaction of [[propyne]] and 4 equivalents of [[N-Butyllithium|butyllithium]] in [[hexanes]].<ref name=PolyLi>{{Cite journal|doi=10.1021/ja01050a040|title=Polylithium compounds III: Polylithium compounds from propyne and 1-butyne, and their polysilicon derivatives|first1=Robert|last1=West|first2=Priscilla C.|last2=Jones|journal=Journal of the American Chemical Society|volume=91|issue=22|date=October 22, 1969}}</ref>{{rp|6156}} | |||
Due to its higher [[lattice energy]], {{chem2|Mg2C3}} is much more stable than {{chem2|Li4C3}}. For example, of the two only the latter reacts explosively with bromine.<ref name=PolyLi/>{{rp|6159}} | |||
===Covalent carbides=== | ===Covalent carbides=== | ||