A family of high-nuclearity [Ln(6)(III)Mn(12)(III)] (Ln = Gd, Tb) nanomagnets has been synthesized, of which two are in D-2 molecular symmetry and the other two are in C-1 symmetry. X-ray crystallography shows that each of them contains a similar {(Mn8O13)-O-III} unit, four marginal Mn-III ions, and two linear {Ln(3)(III)} units with parallel or perpendicular orientation for high- and low-symmetry cores, respectively. For [(Gd6Mn12III)-Mn-III], the distinct spins of the {(Mn8O13)-O-III} unit lead to different spin ground states (S-T = 23 for the high-symmetry one and S-T = 16 for the low-symmetry one), and significant magnetocaloric effects are observed in a wide temperature range [full width at half-maximum (FWHM) of -Delta S-m > 18 K] that can maximizes the refrigerant capacity, which may be attributed to the ferromagnetic interactions. By replacement of isotropic Gd-III with anisotropic Tb-III, they behave as single-molecule magnets, with the high-symmetry one possessing a larger effective barrier (36.6 K) than the low-symmetry one (19.6 K).