The reaction of (Et(4)N)(2)[MoFe3S4Cl3(Cl-4-cat)(CH3CN)], 1, with mercapto carboxylic acids of the general type HSCH(R)COOH affords in nearly quantitative yields the novel double cubanes of the formulation [MoFe3S4Cl3(SCH(R)COO)](4-)(2) (R = H, mercaptoacetate, 2; R = CH3, thiolactate, 3; R = CH2COOH, thiomalate, 4). Black crystals of (Et(4)N)2 are monoclinic, space group C-2/c, with a = 18.959(9) Angstrom, b = 12.657(7) Angstrom, c = 28.57(1) Angstrom, beta = 98.03(4)degrees, V = 6790(5) Angstrom(3), and Z = 4. Black crystals of (Et(4)N)3 are monoclinic, space group C-2/c, with a = 16.281(5) Angstrom, b = 25.13(1) Angstrom, c = 19.019(7) Angstrom, beta = 112.61(2)degrees, V = 7182(4) Angstrom(3), and Z = 4. The solutions of both structures were accomplished by direct methods. The refinement with full-matrix least-squares methods of 299 parameters based on 5942 unique reflections for (Et(4)N)2 (2 theta(max) = 45 degrees, I > 3 sigma(I)) and of 287 parameters based on 4728 unique reflections (2 theta(max) = 45 degrees, I > 3 sigma(I)) for (Et(4)N)3 resulted in final R (R(W)) values of 6.09% (6.26%) and 7.00% (6.52%), respectively, for 2 and 3. In both structures anisotropic temperature factors were assigned for all the non-hydrogen atoms in the cluster tetraanions. The tetraanions in 2 or 3 are composed of two MoFe3S4 subunits linked by the deprotonated thiol groups. In 2, the mean intracubane Mo-S, Fe-S, and Fe-Cl bond distances are found at 2.356(3), 2.278(4), and 2.219(4) Angstrom, respectively.