In the BX family, the last row of Table shows the trend of a strong decrease of the cohesive energy counted per FU with a very low magnitude for X = Bi. Note that for BBi the electronegativity trend is reversed compared to other boron pnictides: (Bi) < (B), so that it can rather be called a "boride", i.e. with negatively charged boron (see next section for an illustration).