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Pentaborane(11)
Identifiers
CAS Number	18433-84-6 ;
3D model (JSmol)	Interactive image;
ChemSpider	34987102;
ECHA InfoCard	100.038.447
EC Number	242-307-4;
UNII	79Z6OH65UV ;
CompTox Dashboard (EPA)	DTXSID901317015 ;
	InChI InChI=1S/B5H11/c1-3-4-2-5(1,3)4/h5H,3-4H2,1-2H3 Key: OPSKXWPMAKCNOG-UHFFFAOYSA-N;
	SMILES [BH3]1[BH2]2[BH]13[BH2]2[BH3]3;
Properties
Chemical formula	B5H11
Molar mass	65.14 g·mol−1
Melting point	−123 °C (−189 °F; 150 K)
Boiling point	63 °C (145 °F; 336 K)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Pentaborane(11) is inorganic compound with the chemical formula B₅H₁₁. It is an obscure boron hydride cluster, especially relative to the heavily studied pentaborane(9) (B₅H₉). With two more hydrogen atoms than nido-pentaborane(9), pentaborane(11) is classified as an arachno- cluster.^[1]

Synthesis

Like many boron hydride clusters, pentaborane(11) was originally obtained from the pyrolysis of diborane. A more systematic synthesis entails treatment of [B₄H₉]⁻ with boron tribromide. The Lewis acid abstracts hydride to give unstable B₄H₈, the precursor to B₅H₁₁:^[2]

[B₄H₉]⁻ + BBr₃ → B₄H₈ + HBBr₃⁻

2 B₄H₈ → B₅H₁₁ + "B₃H₅"

References

^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
^ Toft, Mark A.; Leach, J. B.; Himpsl, Francis L.; Shore, Sheldon G. (1982). "New, Systematic Syntheses of Boron Hydrides via Hydride ion Abstraction Reactions: Preparation of B₂H₆, B₄H₁₀, B₅H₁₁, and B₁₀H₁₄". Inorganic Chemistry. 21 (5): 1952–7. doi:10.1021/ic00135a048.

[1] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[2] Toft, Mark A.; Leach, J. B.; Himpsl, Francis L.; Shore, Sheldon G. (1982). "New, Systematic Syntheses of Boron Hydrides via Hydride ion Abstraction Reactions: Preparation of B₂H₆, B₄H₁₀, B₅H₁₁, and B₁₀H₁₄". Inorganic Chemistry. 21 (5): 1952–7. doi:10.1021/ic00135a048.

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