High-spin molecules have been proposed as candidates for the storage of information at the molecular level. The electronic structure of two complex magnetic molecular systems, Mn-10 and Mn-19, is characterized by means of a computational study based on density functional theory. All the exchange interactions in the recently reported Mn-19 complex with the highest known spin value of 83/2, and in its highly symmetric Mn-10 parent compound, are ferromagnetic. In these complexes, there are two kinds of ferromagnetic coupling: the first one corresponds to Mn-II-Mn-III. interactions through a double mu(2)-alkoxo-mu(4)-oxo bridge where the high coordination number of the Moll cations results in long Mn-II-O bond distances, while the second one involves Mn-III-Mn-III interactions through mu(2)-alkoxo-mu(3)-eta(1):eta(1):eta(1) azido bridging ligands with long Mn-III-N distances due to a Jahn-Teller effect.