Within the transition metal oxide systems, vanadium presents a unique chemistry due to its capacity to form a great number of mixed-valence oxo clusters which often have the peculiarity to incorporate species that function, for size, shape, and charge, as templates. Prismatic, lustrous dark brown crystals of [(n-C4H9)NH3](9)[V19O49]. 7H(2)O are obtained by reacting (n-C4H9NH3)VO3, VOSO4, and (n-C4H9)NH2 in H2O. The X-ray crystal structure shows an ellipsoidal metal-ore cluster formed by 15 VO5 and 3 VO4 polyhedra surrounding an almost regular VO4 tetrahedron located on the 3-fold axis of a trigonal cell of dimensions a = 19.113(5) Angstrom and c = 13.743(5) Angstrom with space soup and Z = 2. Exponentially weighted bond valence sum calculations, manganometric titration of the V-IV centers, and magnetic measurements are consistent with the presence of three localized and three delocalized electrons. Variable-temperature solid-state susceptibility studies indicate antiferromagnetic coupling between V-IV centers. Cyclic voltammetry in acetonitrile shows a irreversible reduction at -1.24 V and a reversible oxidation at +0.17 V (vs Ag/AgCl). The title compound converts quantitatively to the metal oxide K2V3O8 with an extended layered structure as soon as a potassium salt is added to a neutral aqueous solution of the polyoxoanion.