Iron diboride, FeB₂

Iron diboride, FeB₂, has been prepared in a similar manner to the sub-boride, and represents the maximum limit of combination of iron with boron. Its density is 5; it is slightly yellow in colour, hard, and friable, being readily oxidised by moist air.

Other complexes, such as Fe₅B₆, Fe₃B₄, Fe₂B₃, have been prepared, but are probablv not all separate chemical entities.