The hydrolytic stability of borides was studied. It was found that, among the Mg borides, only MgB2 reacted with HCl. Alloys of Mg with MgB2 gave higher yields of B hydrides than did pure MgB2. This was attributed to the hydrogenating effect of H in its so-called nascent state.

Chemical Stability and Structure of Borides. L.Y.Markovskii: Poroshkovaya Metallurgia, 1962, 2[4], 39-45

Figure 7

Substitutional O Atom on a B Plane