Disodium enneaborate

Disodium enneaborate is the traditional name for a salt of sodium, boron, oxygen, and hydrogen, with elemental formula Na2B9H22O20 or Na2B9O9·11H2O. It is the sodium borate with the highest boron/sodium ratio.[1]

Disodium enneaborate
Identifiers
3D model (JSmol)
  • InChI=1S/B8H4O15.BH3O3.2Na.2H2O/c9-1-14-2(10)17-6(16-1)19-7-18-5(13)22-8(23-7)20-3(11)15-4(12)21-8;2-1(3)4;;;;/h9-12H;2-4H;;;2*1H2/q-2;;2*+1;;
    Key: FUFQAFYJPUNFLR-UHFFFAOYSA-N
  • [Na+].[Na+].[O]B1O[B-]2(OB(O)OB(O)O2)OB(O1)O[B-]3OB(O)OB(O)O3.OB(O)O.O.O
Properties
B9H22Na2O20
Molar mass 485.43 g·mol−1
Related compounds
Related compounds
 Borax
Sodium pentaborate
Disodium octaborate
Trisodium borate
Sodium metaborate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Structure

The correct formula has since been determined to be (Na+)2[B8O11(OH)4]2−·B(OH)3·2H2O. The anion is a linear polymer with repeating unit [−B8O11(OH)4−]2−. Sodium cations, water molecules, and undissociated boric acid molecules B(OH)3 lie between the chains, held by numerous hydrogen bonds.[1]

The compound crystallizes in the monoclinic crystal system with space group P21/n. The cell parameters are a = 1021.3 pm, b = 1294.0 pm, c = 1245.7 pm, β = 93.070°, V = 1.6440 nm3, and Z = 2. The sodium cations occur in groups of four with interatomic distances of 378.30 pm and 379.32 pm.[1]

Reactions

Upon heating, disodium enneaborate initially becomes amorphous and then crystallizes as anhydrous disodium octaborate α-Na2B8O13 along with amorphous B2O3. Notably, the former contains octaborate fundamental building blocks that are topologically equivalent to those in the enneaborate.[1]

References
  1. Doinita Neiner, Yulia V. Sevryugina, Larry S. Harrower, and David M. Schubert (2017): "Structure and Properties of Sodium Enneaborate, Na2[B8O11(OH)4]·B(OH)3·2H2O". Inorganic Chemistry, volume 56, issue 12, pages 7175–7181. doi:10.1021/acs.inorgchem.7b00823


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