We report herein the syntheses and investigation of the magnetic properties of a Co-4(II) compound, a series of trinuclear Co(2)(II)Ln(III)(Ln(III) = Nd-III, Sm-III, Gd-III, Tb-III, Dy-III) complexes, and a Co-7(II) complex. The homometallic Co-4(II) core was obtained from the reaction of Ln(NO3)(3)center dot xH(2)O/Co(NO3)(2)center dot 6H(2)O/H(2)vab/Et3N in a 0.5:0.5:1:2 ratio in methanol. Variation in synthetic conditions was necessary to get the desired Co-II-Ln(III) complexes. The Co-II-Ln(III) assembly was synthesized from Ln(NO3)(3).xH(2)O/Co(OAc)(2)(center dot) 4H(2)O/H(2)vab/NaOMe in a 0.4:0.5:1:1 ratio in methanol. The isostructural Co(2)(II)Ln(III) complexes have a core structure with the general formula [Co(2)Ln(Hvab)(4)(NO3)](NO3)center dot MeOH center dot H2O, (where H(2)vab = 2-[(2-hydroxymethyl-phenylimino)-methyl]-6-methoxy-phenol) with simultaneous crystallization of Co-7(II) complex in each reaction. The magnetic investigation of these complexes reveals that both homometallic complexes and four Co-II-Ln(III) complexes (except Co-II-Nd-III) display behavior characteristic of single molecule magnets.