The tridecanuclear heterovalent mixed-metal (Mn11Gd2) complex [MnIII9MnII2GdIII2(O)8(OH)2(O2CR)17(NO3)2(H2O)] has been obtained from the reaction of the hexanuclear compound [Mn6O2(Piv)10(4-Me-py)2.5(PivH)1.5] with Gd(NO3)3·6H2O in CH3CN. The complex presents an unusual "bell"-shaped core with a high-spin ground state and is a new member of the high-nuclearity 3d-4f single-molecule magnets family.