Syntheses, characterization, and magnetic properties of a series of diphenoxo-bridged discrete dinuclear MIILnIII 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 CuIILnIII compounds (Ln = Ce (1), Pr (2), Nd (3), Sm (4), Tb (7), Ho (9), Er (10), and Yb (12)) and three NiIILn III (Ln = Ce (13), Sm (16), and Gd (18)) compounds have been determined. Considering the previously reported structure of the Cu IIGdIII (6) compound (Eur. J. Inorg. Chem. 2005, 1500), a total of twelve structures are discussed/compared in this study. Four types of composition are observed in the CuIILnIII complexes: [CuIILLnIII (NO3)3(H2O)] (1-3: Ln = Ce-Nd), [CuIILSmIII(NO3) 3]·CH3COCH3 (4), [CuII(H 2O)LLnIII(NO3)3] (5: Ln = Eu; 6: Ln = Gd), and [CuIILLnIII(NO3)3] (4A: Ln = Sm; 7-12: Ln = Tb-Yb). On the other hand, the NiIILn III complexes are characterized to have two types of composition: [NiIILLnIII(H2O)(NO3)3] (13-15: Ln = Ce-Nd) and [NiIILLnIII(NO3) 3]·0.5CH3COCH3 (16-24: Ln = Sm-Yb). Among twelve X-ray structures, seven belong to three different isomorphous sets (CuIICeIII (1), CuIIPrIII (2), CuIINdIII (3), and NiIICeIII (13); CuIITbIII (7), CuIIHoIII (9), CuIIErIII (10), and CuIIYbIII (12); NiIISmIII (16) and NiIIGdIII (18)), whereas space group/unit cell parameters of two others (CuIISm III (4) and CuIIGdIII (6)) are of different types. The lanthanide(III) centers in CuIICeIII (1), CuIIPrIII (2), CuIINdIII (3), and NiIICeIII (13) complexes are eleven-coordinated, while the lanthanide(III) centers in other compounds are ten-coordinated. As evidenced from the dihedral angle (σ) between the CuO(phenoxo)2 and LnO(phenoxo)2 planes, variation in the extent of planarity of the bridging moiety in the CuIILnIII compounds takes place; the ranges of σ values are 0.8-6.2° in the 4f1-7 analogues and 17.6-19.1° in the 4f8-13 analogues. The Cu IIGdIII (6) compound exhibits ferromagnetic interaction (Eur. J. Inorg. Chem. 2005, 1500). The nature of the magnetic exchange interaction in the CuIILnIII complexes has been understood by utilizing the empirical approach; the NiIILnIII complexes have been used as references. The metal centers in the Eu III complex are uncorrelated, while other 4f1-6 analogues (CeIII, PrIII, NdIII, and SmIII) exhibit antiferromagnetic interaction. Among the higher analogues (4f 7-13), only YbIII exhibits antiferromagnetic interaction, while interaction in other analogues (GdIII, TbIII, DyIII, HoIII, ErIII, and TmIII) 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. © 2010 American Chemical Society.