Octahydrotriborate

Octahydrotriborate
Identifiers
CAS Number	12429-74-2 ;
3D model (JSmol)	Interactive image;
	InChI InChI=1S/B3H8/c4-1-2-3(1,4)5-2/h1-3H2/q-1 Key: QWUBYVSCVASZDU-UHFFFAOYSA-N;
	SMILES [BH2]12[H][BH2-]13[H][BH2]23;
Properties
Chemical formula	B3H8−
Molar mass	40.49 g·mol−1
Appearance	colorless
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Octahydrotriborate is the boron hydride anion B₃H₈⁻. It forms a variety of salts that are colorless and air-stable. The tetrabutylammonium salt is soluble in organic solvents such as acetonitrile and methylene chloride. The anion is an intermediate is the synthesis of various higher boron hydrides, such as pentaborane(9). B₃H₈⁻ can be viewed as the conjugate base of triborane B₃H₉.

Preparation

Octahydrotriborate is prepared by partial oxidation of borohydride with iodine or boron trifluoride:^[2]

3 BH₄⁻ + I₂ → B₃H₈⁻ + 2 H₂ + 2 I⁻

5 BH₄⁻ + 4 BF₃O(C₂H₅)₂ → 2 B₃H₈⁻ + 2 H₂ + 4 O(C₂H₅)₂ + 3 BF₄⁻

Structure and reactions

As shown by X-ray crystallography of various salts, B₃H₈⁻ consists of a distorted triangle of three BH₂ vertices. Two edges of the triangle are occupied by bridging hydrides.^[3]

It is converted to the bromide B₃H₇Br⁻ using HBr (illustrating its hydridic character):

B₃H₈⁻ + HBr → B₃H₇Br⁻ + H₂

Pyrolysis of this bromide gives pentaborane(9).^[4]

5 B₃H₇Br⁻ → 3 B₅H₉ + 5 Br⁻ + 4 H₂

Also consistent with its basicity, B₃H₈^_ functions as a bidentate ligand in a variety of coordination complexes, e.g. Cr(B₃H₈)₂.^[5]

References

^ Macintyre, Jane E. (1993-07-15). Dictionary of Inorganic Compounds, Supplement 1. CRC Press. p. 366. ISBN 978-0-412-49090-3.
^ Ryschlewitsch, G. E.; Nainan, K. C. (1974). Octahydrotriborate (1-) ([B3 H8 ]) salts. Inorganic Syntheses. Vol. 15. pp. 111–118. doi:10.1002/9780470132463.ch25. ISBN 9780470132463.
^ Dunbar, Andrew C.; Macor, Joseph A.; Girolami, Gregory S. (2014). "Synthesis and Single Crystal Structure of Sodium Octahydrotriborate, NaB₃H₈". Inorganic Chemistry. 53 (2): 822–826. doi:10.1021/ic402127x. PMID 24380447.
^ Miller, V. R.; Ryschkewitsch, G. E. (1974). Pentaborane(9) (B₅H₉). Inorganic Syntheses. Vol. 15. pp. 118–122. doi:10.1002/9780470132463.ch26. ISBN 9780470132463.
^ Goedde, Dean M.; Girolami, Gregory S. (2004). "A New Class of CVD Precursors to Metal Borides: Cr(B₃H₈)₂ and Related Octahydrotriborate Complexes". Journal of the American Chemical Society. 126 (39): 12230–12231. doi:10.1021/ja046906c. PMID 15453732.

[1] Macintyre, Jane E. (1993-07-15). Dictionary of Inorganic Compounds, Supplement 1. CRC Press. p. 366. ISBN 978-0-412-49090-3.

[2] Ryschlewitsch, G. E.; Nainan, K. C. (1974). Octahydrotriborate (1-) ([B3 H8 ]) salts. Inorganic Syntheses. Vol. 15. pp. 111–118. doi:10.1002/9780470132463.ch25. ISBN 9780470132463.

[3] Dunbar, Andrew C.; Macor, Joseph A.; Girolami, Gregory S. (2014). "Synthesis and Single Crystal Structure of Sodium Octahydrotriborate, NaB₃H₈". Inorganic Chemistry. 53 (2): 822–826. doi:10.1021/ic402127x. PMID 24380447.

[4] Miller, V. R.; Ryschkewitsch, G. E. (1974). Pentaborane(9) (B₅H₉). Inorganic Syntheses. Vol. 15. pp. 118–122. doi:10.1002/9780470132463.ch26. ISBN 9780470132463.

[5] Goedde, Dean M.; Girolami, Gregory S. (2004). "A New Class of CVD Precursors to Metal Borides: Cr(B₃H₈)₂ and Related Octahydrotriborate Complexes". Journal of the American Chemical Society. 126 (39): 12230–12231. doi:10.1021/ja046906c. PMID 15453732.

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