Syntheses, characterization, and magnetic properties of a series of diphenoxo-bridged discrete dinuclear M(II)Ln(III) complexes (M = Cu or Ni, Ln. Ce-Yb) derived from the compartmental Schiff base ligand, H2L, obtained on condensation of 3-ethoxysalicylaldehyde with trans-1,2-diaminocyclohexane, are described. Single crystal X-ray structures of eight Cu(II)Ln(III) compounds (Ln = Ce (1), Pr (2), Nd (3), Sm (4), Tb (7), Ho (9), Er (10), and Yb (12)) and three Ni(II)Ln(III) (Ln = Ce (13), Sm (16), and Gd (18)) compounds have been determined. Considering the previously reported structure of the (CuGdIII)-Gd-II (6) compound (Eur. J. lnorg. Chem. 2005, 1500), a total of twelve structures are discussed/compared in this stucy. Four types of composition are observed in the Cu(II)Ln(III) complexes: [Cu(II)LLn(III) (NO3)(3)(H2O)] (1-3: Ln = Ce-Nd), [(CuLSmIII)-L-II(NO3)(3)]center dot CH3COCH3 (4), [Cu-II(H2O)LLn(III)(NO3) (5: Ln = Eu; 6: Ln = Gd), and [CulILLnul(NO3)(3)] (4A: Ln = Sm; 7-12: Ln = Tb-Yb). On the other hand, the NinLrim complexes are characterized to have two types of composition: [Ni(II)LLn(III)(H2O)(NO3)31 (13-15: Ln = Ce-Nd) and [Ni(II)LLn(III)(NO3)3] " 0.5CH(3)COCH(3) (16-24: Ln = Sm-Yb). Among twelve X-ray structures, seven belong to three different isomorphous sets ((CuCeIII)-Ce-II (1), (CuPrIII)-Pr-II (2), (CuNdIII)-Nd-II (3), and (NiCeIII)-Ce-II (13); (CuTbIII)-Tb-II (7), CullHol" (9), CuIIErIII (10), and CullYbIll (12); (16) and NillGe (18)), whereas space group/unit cell parameters of two others (CullSmIll (4) and Cull-uo (6)) are of different types. The lanthanide(III) centers in Cute (1), Cu II ',rill (2), CuliNdIll (3), and Niii-eiii L, (13) complexes are eleven-coordinated, while the lanthanide(III) centers in other compounds are tencoordinated. As evidenced from the dihedral angle (6) between the CuO(phenoxo)2 and LnO(phenoxo)2 planes, variation in the extent of planarity of the bridging moiety in the CuIlLnill compounds takes place; the ranges of 6 values are 0.8-6.2 degrees in the 4f(1-7) analogues and 17.6-19.1 degrees in the 4f(8-13) analogues. The CutclIll (6) compound exhibits ferromagnetic interaction (Eur. J. lnorg. Chem. 2005, 1500). The nature of the magnetic exchange interaction in the CuIlLnIll complexes has been understood by utilizing the empirical approach; the NillLnIll complexes have been used as references. The metal centers in he Eu-III complex are uncorrelated, while other 4f(1-6) analogues (Celli, Pr", Nclul, and SmIll) exhibit antiferromagnetic interaction. Among the higher analogues (4f(7-13)), only Yb-III exhibits antiferromagnetic interaction, while interaction in ot ler analogues (GclIll,, Ho Er", and Tel) is ferromagnetic. An important aspect of the present study is the measurement of the magnetic susceptibility of the unblocked samples as well as on blocking the samples with grease to avoid powder reorientation, if any. Comparison of the two sets of data reveals significant difference in some cases.