Our explorations of the reactivity of Fe/Mo/S clusters of some relevance to the FeMoco nitrogenase have led to new double-fused cubane clusters with the Mo2Fe6S8 core as derivatives of the known (Cl-4-cat)(2)Mo2Fe6S8(PPr3)(6) (1) fused double cubane. The new clusters have been obtained by substitution reactions of the PPr3 ligands with Cl-, BH4-, and N-3(-). By careful control of the conditions of these reactions, the clusters [(Cl-4-cat)(PPr3)MoFe3S4(BH4)(2)](2)(Bu4N)(4) (11), [(Cl-4-cat)(PPr3)MoFe3S4(PPr3)(BH4)](2)(Bu4N)(2) (111), RCl4-cat)(PPr3)MoFe3S4(N-3)(2)](2)(Bu4N)(4) (IV), [(Cl(4-)cat) (PPr3)MoFe3S4(PPr3)(N-3)](2)(Bu2N)(2) (V), and [(Cl-4-cat)(PPr3)MoFe3S4Cl2](2)(Et4N)(4) (VI) have been obtained and structurally characterized. A study of their electrochemistry shows that the reduction potentials for the derivatives of I are shifted to more positive values than those of 1, suggesting a stabilization of the reduced clusters by the anionic ligands BH4- and N-3(-). Using H-1 NMR spectroscopy, we have explored the lability of the BH4- ligand in 11 in coordinating solvents and its hydridic character, which is apparent in its reactivity toward proton sources such as MeOH or PhOH,