A new family of pentanuclear 3d-4f heterometal complexes of general composition [Ln(2)(III)((ML)-L-II)(3)(mu(3)-O)(3)H](ClO4)center dot xH(2)O (1-5) [Ln = Nd, M = Zn, 1; Nd, Ni, 2; Nd, Cu, 3; Gd, Cu, 4; Tb, Cu, 5] have been synthesized in moderate yields (50-60%) following a self-assembly reaction involving the hexadentate phenol-based ligand, viz., N,N-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-N',N'-diethylethylenediamine (H2L). Single-crystal X-ray diffraction analyses have been used to characterize these complexes. The compounds are all isostructural, having a 3-fold axis of symmetry that passes through the 4f metal centers. The [(ML)-L-II] units in these complexes are acting as bis-bidentate metalloligands and, together with mu(3)-oxido bridging ligands, complete the slightly distorted monocapped square antiprismatic nine-coordination environment around the 4f metal centers. The cationic complexes also contain a H+ ion that occupies the central position at the 3-fold axis. Magnetic properties of the copper(II) complexes (3-5) show a changeover from antiferromagnetic in 3 to ferromagnetic 3d-4f interactions in 4 and 5. For the isotropic (CuII-GdIII) compound 4, the simulation of magnetic data provides very weak Cu-Gd (J(1) = 0.57 cm(-1)) and Gd-Gd exchange constants (J(2) = 0.14 cm(-1)). Compound 4 is the only member of this triad, showing a tail of an out-of-phase signal in the ac susceptibility measurement. A large-spin ground state (S = 17/2) and a negative value of D (-0.12 cm(-1)) result in a very small barrier (8 cm(-1)) for this compound. Among the three (Nd2M3II)-M-III (M = Zn-II,Ni-II, and Cu-II) complexes, only the Zn-I analogue (1) displays an NIR luminescence due to the 4F(3/2) -> I-4(11/2) transition in Nd-III when excited at 290 nm. The rest of the compounds do not show such Nd-III/Tb-III-based emission. The paramagnetic Cu-II and Ni-II ions quench the fluorescence in 2-5 arid thereby lower the population of the triplet state.