The exchange coupling constants of two Mn(17) complexes have been analyzed; one of them has the second largest ground-state spin value reported up to now, being the largest-spin single-molecule magnet. The two complexes show a two-edge-sharing supertetrahedra structural motif, Mn(II)(6)Mn(III)(11), and similar ligands, but they show different total spin values. One of them has the highest possible, S = 37, while for the second complex, the S value is lower and equal to 28 ± 1. The calculated J values using DFT methods for both systems indicate the predominance of the ferromagnetic interactions consistent with the S = 37 total spin. The analysis of similar Mn(19) complexes with the two supertetrahedra sharing one vertex gives similar results, pointing out the preponderance of the ferromagnetic couplings.