Chemistry:Octadecaborane

Octadecaborane(22)
	File:B18H22 from Xray coordinates.tif
	File:Iso-B18H22 from Xray coordinates.tif
Names
	Other names octadecaborane; octadecaboron doicosahydride; octodecaborane; n-Octadecaborane; i-Octadecaborane
Identifiers
CAS Number	21107-56-2 ;
EC Number	695-976-3;
Properties
Chemical formula	B18H22
Molar mass	216.77 g/mol
Appearance	White to off white powder
Density	1.012 g/cm3
Melting point	180 and 129 °C (356 and 264 °F; 453 and 402 K) n-B18H22 and i-B18H22 respectively
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Octadecaborane is an inorganic compound, a borane with chemical formula B₁₈H₂₂. It is a colorless flammable solid, like many higher boron hydrides. Although the compound has no practical applications, its structure is of theoretical and pedagogical interest.

Synthesis

It is formed by oxidative degradation of B₂₀H₁₈²⁻ or by oxidative coupling of B₉H₁₂⁻.

Structure

Two isomers are known of octadecaborane, providing the first example of isomers in a boron-hydride cluster. The clusters are also of interest because the boron centers shared between the two subunits have an unusually high number of B-B interactions. The isomers consists of two B₉H₁₁ polyhedral subunits, each having a decaborane-like form, joined at a B–B edge.^[1]^[2] These two boron atoms are each coordinated to six others; this compound was the first one found to have such a high number of borons coordinated around a single boron center.^[3] There are two different geometric isomers of this compound, differing in the orientation of the two edge-fused polyhedra to each other.^[1]^[2] This compound was the first borane found to have multiple isomeric forms.^[4] Among the geometric isomers, one with chirality was the first borane to be resolved into its separate enantiomers, and was only the second chiral borane known at that time.^[5]

References

↑ ^1.0 ^1.1 Olsen, Frederic P.; Vasavada, Ravindra C.; Hawthorne, M. Frederick (1968). "The chemistry of n-B₁₈H₂₂ and i-B₁₈H₂₂". J. Am. Chem. Soc. 90 (15): 3946–3951. doi:10.1021/ja01017a007.
↑ ^2.0 ^2.1 Londesborough, Michael G.S.; Hnyk, Drahomír; Bould, Jonathan; Serrano-Andrés, Luis; Sauri, Vicenta; Oliva, Josep M.; Kubát, Pavel; Polívka, Tomáš et al. (2012). "Distinct Photophysics of the Isomers of B₁₈H₂₂ Explained". Inorg. Chem. 51 (3): 1471–1479. doi:10.1021/ic201726k. PMID 22224484.
↑ Simpson, P. G.; Lipscomb, W. N. (1962). "Molecular Structure of B₁₈H₂₂". Proceedings of the National Academy of Sciences of the United States of America 48 (9): 1490–1491. doi:10.1073/pnas.48.9.1490. PMID 16590990. PMC 220984. Bibcode: 1962PNAS...48.1490S. http://www.pnas.org/content/48/9/1490.full.pdf.
↑ Simpson, Paul G.; Folting, Kirsten; Lipscomb, William N. (1963). "The Molecular Structure of i-B₁₈H₂₂". J. Am. Chem. Soc. 85 (12): 1879–1880. doi:10.1021/ja00895a046.
↑ Heřmánek, S.; Plešek, J. (1970). "Chemistry of boranes. XXI. Resolution of iso-octadecaborane to optical enantiomers". Collection of Czechoslovak Chemical Communications 35 (8): 2488–2493. doi:10.1135/cccc19702488.