Two novel Mn12 derivs., [Mn12O12(O2CCCH)16(H2O)4].3H2O (1) and [Mn12O12(O2CCCC6H5)16(H2O)4].3H2O (2) were prepd. and characterized. Magnetic measurements confirm that both function as single-mol. magnets (SMM), showing frequency-dependent out-of-phase a.c. susceptibility signals and magnetization hysteresis curves. Thermal stability studies of both complexes were 1st conducted in the solid state. While complex 1 undergoes a sudden exothermal decompn. at Tonset = 118°, complex 2 exhibits a higher stability. Thermolysis reaction of 1 was hence assessed in soln. to yield dark red crystals of a two-dimensional MnII-based coordination polymer, [Mn3(O2CCCH)6(H2O)4].2H2O (3), which corresponds to an extended sheet-like structure that crystallizes in the monoclinic space group P21/n; a 9.2800(2), b 9.4132(2), c 14.9675(3) .ANG., b 99.630(1)°, and Z = 2. Finally, the magnetic properties of complex 3 were studied on an oriented single crystal over two different orientations of the reciprocal vector vs. the external field.