# Hydrolysis of magnesium boride

Does magnesium boride react with water to form boranes?

My attempt:

Magnesium nitride reacts with water to form ammonia and magnesium hydroxide.

Similarly, does magnesium boride also react with water to form a borane and magnesium hydroxide?

Hydrolysis of magnesium boride has previously been attempted1. Two hydrolysis products were observed. The main hydrolysis product was found to be $$\ce{Mg3B2(OH)6}$$ but at $$\pu{-10 ^\circ C}$$, a different product is formed whose composition was found to be $$\ce{H3B2(MgOH)3}$$ which immediately converts back to the main product if the temperature were slightly increased. The corresponding reactions were:

$$\ce{Mg3B2 + 6H2O -> Mg3B2(OH)6 + 3H2}$$ $$\ce{Mg3B2 + 3H2O -> H3B2(MgOH)3}$$ $$\ce{H3B2(MgOH)3 + 3H2O -> Mg3B2(OH)6 + 3H2}$$

No boric acid, magnesium borate or even boranes were formed although these products were expected from the hydrolysis reaction.

Reference

1. The hydrolysis of magnesium boride by Rames C. Ray and Prafulla C. Sinha , J. Chem. Soc., 1935, 1694-1695, DOI: 10.1039/JR9350001694 (PDF)
• The compound $\ce{Mg_3B_2(OH)_6}$ seems to be made of $3$ $\ce{Mg(OH)_2}$ + $2$ atoms of elementary Boron. It looks as if Boron had been oxidized from $-3$ to $0$. Strange reaction ! Everything looks as if both Mg and B are at the oxidation number of zero in magnesium boride !!! Never seen such a strange reaction ! – Maurice Jul 31 '20 at 16:40
• Are there other borides which gets hydrolsed to form boranes? – Neville S Vempeny Aug 2 '20 at 5:20
• @NevilleVempeny Not that I know of, but action of dilute acids on magnesium boride gives various types of boranes especially $\ce{B4H10}$. See here and here for reference. – Nilay Ghosh Aug 2 '20 at 8:16
• @Maurice I think there is something even more strange. We are speaking of $\ce{Mg3B2}$, but does this even exist? Magnesium-boron phase diagram I've seen show no compound with stoichiometry $\ce{MgB_x}$ for any $x<2$. – Oscar Lanzi Dec 15 '20 at 19:20