Following a recent study of boron-containing compounds for use as fuels, we follow up here with calculations of the thermodynamic properties of mixed boron–nitrogen compounds; specifically, two isomers of diazadiboretidine, cyclo-B2N2H4. The 1,2-isomer has similar atoms adjacent in the ring, while the 1,3-isomer alternates boron and nitrogen atoms in the ring. Our results indicate that the combustion energies are about 31–38 kJ/g, making these compounds better than many small ringed compounds but still less than methane on a per-gram basis.