The experimental structures of Cp4M4B4H4 (M = Co, Ni) are both bisdisphenoids. However, in the cobalt compound, the metal atoms are located at the four degree 5 vertices, whereas in the nickel compound the metal atoms are located at the four degree 4 vertices. Density functional theory has shown these structures to be the lowest-energy structures by the substantial margins of around 23 and 15 kcal/mol for M = Co and Ni, respectively. The unknown analogous tetraferraborane Cp4Fe4B4H4 was predicted to have a different type of structure, namely a tetracapped tetrahedron, with the iron atoms at the four degree 6 vertices, similarly to the experimental structure of the valence isoelectronic Cp4Fe4(μ3-CO)4. The experimentally unknown Cp4M4B2H2 and Cp4M4 systems have also been optimized. Addition of BH units to either Cp4M4B2H2 or Cp4M4 to give the corresponding Cp4M4B4H4 derivatives has been predicted to be extremely exothermic.