carborane
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What is a carborane?
A carborane is a thermally stable organometallic compound containing carbon, boron, and hydrogen. Carboranes have the general formula (C_2B_nH_{n+2}), where n ranges from 3 to 10. These compounds have polyhedral molecular structures that consist of networks of boron and carbon atoms, where the carbon atoms are in adjacent positions.
Carboranes are prepared through the reaction of acetylene or acetylene derivatives with boron hydrides. The most common carborane is ortho-carborane, (C_2B_{10}H_{12}), which is created by reacting acetylene with decaborane in the presence of diethyl sulfide. Carboranes are used in the synthesis of polymers and lubricants and have applications in fields such as hydrogen storage and medicine.
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What elements make up a carborane molecule?
Carborane molecules are organometallic compounds containing carbon, boron, and hydrogen. Their general formula is C2BnHn+2, where n ranges from 3 to 10. Carboranes feature polyhedral molecular structures with boron and carbon atoms in networks where carbon atoms are adjacent.
These structures resemble isoelectronic polyhedral boranes, involving three-center bonds and ordinary two-center bonds. A key structural feature is the covalent bonding of carbon to five or six other atoms simultaneously. Carboranes are thermally stable and used in synthesizing polymers and lubricants.
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What unique shape do carborane molecules have?
Carborane molecules have a polyhedral structure that consists of a network of boron and carbon atoms. These atoms occupy adjacent positions in the molecule. Carboranes have similar structures to polyhedral boranes that possess the same number of electrons. The most distinctive feature of carboranes is the covalent bonding of carbon to five or six other atoms.
The most studied carborane is ortho-carborane, or (C_2B_{10}H_{12}). Its molecular structure resembles an icosahedron, with 10 boron atoms and two carbon atoms forming the apices.
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How are carboranes different from other chemical compounds?
Carboranes are a class of organometallic compounds containing carbon, boron, and hydrogen, with the general formula (C_2B_nH_{n+2}).
Their molecular structures are polyhedral networks of boron and carbon atoms, where carbon atoms occupy adjacent positions. Carboranes' structures resemble those of isoelectronic polyhedral boranes, featuring three-center bonds and ordinary two-center bonds. A key structural feature is the covalent bonding of carbon to five or six other atoms simultaneously.
Carboranes are generally produced through the reaction of acetylene or acetylene derivatives with boron hydrides. The nomenclature of carboranes uses the same structural prefixes as boranes (closo-, arachno-, etc.).
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What special properties do carboranes have?
Carboranes are a class of organometallic compounds containing carbon, boron, and hydrogen, with the general formula (C_2B_nH_{n+2}). These compounds have polyhedral molecular structures featuring networks of boron and carbon atoms, where carbon atoms occupy adjacent positions.
Carboranes are thermally stable. Most closo-carboranes can withstand temperatures up to 400 °C (750 °F) without degrading. The three isomeric icosahedral closo-carboranes of formula (C_2B_{10}H_{12}) are easy to prepare and stable in the air.
Carboranes are used in the synthesis of polymers and lubricants. They can also combine with transition metals to form metallacarboranes, some of which display catalytic activity.
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How are carboranes used in science and technology?
Carboranes are a class of organometallic compounds containing carbon, boron, and hydrogen, with the general formula (C_2B_nH_{n+2}). These thermally stable compounds have polyhedral molecular structures featuring networks of boron and carbon atoms.
Carboranes are used in the synthesis of polymers and lubricants. Thousands of carboranes have been prepared and combined with transition metals, yielding metallacarboranes, some of which demonstrate catalytic activity. The most studied carborane is ortho-carborane, (C_2B_{10}H_{12}), which is produced through the reaction of acetylene with decaborane in the presence of diethyl sulfide.
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carborane, any member of a class of organometallic compounds containing carbon (C), boron (B), and hydrogen (H). The general formula of carboranes is represented by C2BnHn + 2, in which n is an integer; carboranes with n ranging from 3 to 10 have been characterized.
The first carboranes were produced in the 1950s, but the results were not declassified and published until 1962–63. Since then, many thousands of carboranes have been prepared, and they have been combined with transition metals to yield derivatives called metallacarboranes, some of which show catalytic activity.
Structure and bonding of carboranes
The carboranes have polyhedral molecular structures based on networks of boron and carbon atoms, in which the carbon atoms occupy adjacent positions. As a result, the structures of carboranes and their derivatives are similar to those of the isoelectronic (possessing the same number of electrons) polyhedral boranes, and, like the boranes, they involve three-centre bonds as well as ordinary two-centre bonds. Their most significant structural feature is the covalent bonding of carbon simultaneously to five or six other atoms.
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In addition, the nomenclature of carboranes employs the same structural prefixes (closo-, arachno-, etc.) as those of borane. The numbering of the atoms in carborane compounds begins with the apex atom of lowest coordination (i.e., with the fewest bonds), and polyhedral vertex atoms are numbered in a clockwise direction with the carbon atoms being given the lowest possible numbers. The best-studied carborane is ortho-carborane, C2B10H12, made by reaction of acetylene with decaborane in the presence of diethyl sulfide. Its molecular structure resembles an icosahedron with the 10 boron atoms and two adjacent carbon atoms forming the apices.
Reactions and synthesis of carboranes
Carboranes are generally prepared by reaction of acetylene or acetylene derivatives with boron hydrides.The first three carboranes—trigonal bipyramidal 1,5-C2B3H5; the 1,2- and 1,6- isomers of octahedral C2B4H6; and pentagonal pyramidal 2,4-C2B5H7—that were produced in the 1950s were generated in low yield by the reaction of pentaborane(9) with acetylene in a silent electric discharge. As is the case with boranes, the nido- and arachno-carboranes are less thermally stable and reactive toward air and chemical reagents than the corresponding closo-carboranes, most of which are stable to 400 °C (750 °F), although they may rearrange to more stable isomeric forms.
The three isomeric icosahedral closo-carboranes of formula C2B10H12 are unusual both in their ease of preparation and their stability in air. Not only has their chemistry been the most extensively studied of all carboranes, but their discovery ushered in the rapid development of the field. Although their systematic International Union of Pure and Applied Chemistry (IUPAC) name is closo-dicarbadodecaborane(12), the three isomers are often simply called ortho-, meta-, and para-carborane.
The most common carborane, the ortho-isomer, has been available in multikilogram quantities since the early 1970s and is best prepared by the reaction of acetylene, C2H2, with decaborane(14) in the presence of a Lewis base such as diethyl sulfide, (C2H5)2S.
nido-B10H14 + 2(C2H5)2S → B10H12{S(C2H5)2}2 + H2
B10H12{S(C2H5)2}2 + C2H2 → closo-1,2-C2B10H12 + 2(C2H5)2S + H2
The two other isomers are prepared by thermal isomerization of the 1,2- (ortho-) isomer.
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Numerous derivatives of icosahedral closo-carboranes, especially of 1,2-C2B10H12, have been prepared by replacement of hydrogen atoms by other groups. Despite their stability toward heat and reagents, the American chemist M. Frederick Hawthorne in 1964 showed that they could be degraded to nido-carborane anions by reaction with strong bases in protonic solvents (those capable of donating H+ ions); for example, closo-1,2-C2B10H12 + RONa + 2ROH → Na[nido-7,8-C2B9H12] + B(OR)3 + H2 (where R is an alkyl group). These nido-anionic cages, called dicarbollide ions (from Spanish olla, meaning “bowl”) led to the preparation of metallacarboranes with their own extensive chemistry.
The first hypho-carborane, C3B4H12, was reported in 1993 by Robert Greatrex, Norman N. Greenwood, and their colleagues.