New Schiff base ligand H2L containing N2O4S donor atoms has been explored for its ability to provide complexes of selected 3d and 4f metal ions. Room temperature reaction of H2L with NiCl2 center dot 6H(2)O and Ln(NO3)(3)center dot 5H(2)O in the presence of Et3N in MeCN-MeOH (2:1) medium resulted in [Ni(4)Ln(2)(L)(2)(mu-Cl)(2)(mu(3)-OH)(4)(H2O)(6)]Cl-4 center dot 2H(2)O (where Ln = Dy3+ (1), Tb3+ (2), and Ho3+ (3) and H2L = 2-(2-(2-(2-hydroxy-3-methoxybenzylideneamino)ethylthio)ethylimino)methyl)-6-methoxyphenol). Use of Ni(SCN)(2)center dot 4H(2)O during synthesis provided SCN- ions for bridging and terminal coordination in [Ni(4)Ln(2)(L)(2)(mu-NCS)(2)(mu(3)-OH)(4) (NCS)(4) (H2O)(2)]center dot XMeOH center dot yH(2)O (where Ln = Dy3+ (4), x = 2, y = 4; Tb3+ (5) and Ho3+ (6), x = 0, y = 14.1). All six complexes possess a hexanuclear defective tetracubane topology having exchangeable bridging groups. The study of direct current magnetic susceptibility measurements revealed that the Ni(II) ions are engaged in ferromagnetic interaction with the Dy-III, Tb-III and Ho-III ions and have significant magnetic anisotropy in all six complexes. Alternating current susceptibility measurements confirmed that both of the two types of compounds qualify as zero-field single molecule magnets (SMMs), and the effective barrier for the reversal of the magnetic moment was found to be in the range U-eff = 23-31 K for 1-2 and 4-5, respectively. Detailed insight into the electronic structure and magnetic properties was calculated using DFT- and CASSCF-based analyses. The found isotropic exchange parameter (I) values are J(Ni-Ni) = -4.7 cm(-1) for 1 and J(Ni-Ni) = +29.2 cm(-1) for 4 and clearly indicate that the mu-NCS-bridge is a better candidate than mu-Cl for ferromagnetic exchange interactions. Out of the six complexes, only complex 5 displays Tb-III centered emission peaks at 451 and 480 nm.