The present paper presents a comprehensive study of the electronic structure of nano-scale molecular oxide capsules of the type [{M^VI(M^VI)₅O₂₁}₁₂{M'^V₂O₂(µ-X)(µ-Y)(L^n-)}₃₀]^(12+n)-, where M,M’=Mo, W, and the bridging ligands X,Y=O,S, carried out by means of density functional theory. Discussion of the electronic structure of these derivatives is focused on the thermodynamic stability of each of the structures, the one having the highest gap being M=W, M’=Mo, X=Y=S. For the most well known structure M=M’=Mo, X=Y=O, [Mo₁₃₂O₃₇₂]^12-, the chemical of several ligands to the {Mo^V₂O₂(μ-O)₂} linker moiety produces negligible effects on its stability which is evidence of a strong ionic component in these bonds. The existence of hitherto unknown species, namely W₁₃₂ with both bridging alternatives is discussed and put into context with our findings.