Please don't say sodium tetraborate decahydrate since that is not the real composition of borax.

Borax contains tetranuclear coordination complexes $\ce{[B4O5(OH)4]^-^2}$. I'm asking about the name of this complex in borax.


1 Answer 1


The name suggested here (via the question comments), the anion-corresponding part, ‘bicyclo[3.3.1]tetraboroxane-3,7-diolate’ ($\ce{[B4O5(O)2]^2-}$) obviously does not match with the tetraborate formula $\ce{[B4O5(OH)4]^2-}$ present in borax, whose structure, confirmed by X-ray crystallography, including hydrogens[1], is

Fig.1 Tetraborate anion

However, the ‘bicyclo[3.3.1]tetraboroxane’ part is correct, for the parent hydride:

Fig.2 Bicyclotetraboroxane

This type of names is known e.g. for the ‘cyclotriboroxane’ name for boroxine, or ‘cyclotetrasiloxane’ (in octamethylcyclotetrasiloxane).

So the name would be rather 1,3,5,7-tetrahydroxybicyclo[3.3.1]tetraboroxane, or bicyclo[3.3.1]tetraboroxane-1,3,5,7-tetrol, however it still does not explicitly tell that it's an anion.

Interestingly, this boroxane, siloxane type names (interchanging element/oxygen pattern) is rather marginally mentioned in the inorganic nomenclature, notably more detailed in the organic nomenclature.[2]

Inorganic additive nomenclature is able to constructs names for similar skeletons,[3] but somewhat differently than organic nomenclature.

E.g. bicyclo[x.y.z]Nane (where N is the numerical prefix root, with the exception for 1..4, ‘meth’..‘but’, for the organic names) would be named: Ncarby-[0a.z1,b]dicycle, where a = x+y+2 and b = x+2. If the structure is an ion, it's ‘…cyclate’ followed by the charge in parentheses. One advantage is that the first numeral is the size of the (largest) cycle, not just a branch.

Some examples from the book:

Example 1

(IR- Example 6)

Example 2

cyclo-triphosporic acid
(IR-8.3 Example 5)

Example 3

(IR-7.4.3 Example 11)

(The leading zero in the first numeral in the square brackets is intentional for the cycles, however in the latter example, it's not used, despite IR-7.4.2 Nodal descriptor, example 3, that states that the nodal descriptor for hexacycle is ‘06’.)

With this nomenclature we can get very descriptive (but almost unusable) names
1,3,5,7-tetrahydroxidotetrabory-2,4,6,8,9-pentaoxy-[08.11,5]dicyclate(2−), or


  1. Levy H.A., Lisensky G.C. Crystal structures of sodium sulfate decahydrate (Glauber's salt) and sodium tetraborate decahydrate (borax). Redetermination by neutron diffraction Acta Crystallographica Section B 34 (1978): p. 3507
  2. IUPAC Blue Book 2013, P-
  3. IUPAC Red Book 2005, IR-7.4 Additive nomenclature: Inorganic chains and rings
  • 1
    $\begingroup$ snort dicyclate! :D Yep, that almost unusable, indeed... $\endgroup$
    – Mithoron
    Jun 3, 2020 at 15:35

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