Three novel ferrocenecarboxylato-bridged lanthanide dimers [Gd-2(mu(2)-OOCFC)(2)(OOCFC)(4)(MeOH)(2)(H2O)(2).2MeOH.2H(2)O (1) (Fc = (eta(5)-C5H5)Fe(eta(5)-C5H4)), [Nd-2(mu(2)-OOCFC)(2)(OOCFC)(4)(H2O)(4)].2MeOH.H2O (2), and [Y-2(mu(2)-OOCFC)(2)(OOCFc(4)(H2O)(4)].2MeOH (3) have been synthesized and characterized by single-crystal X-ray crystallography. In each complex, two Ln(III) (Ln = Gd, Nd, or Y) ions are bridged by two ferrocenecarboxylate anions as asymmetrically bridging ligands, leading to dimeric cores, [Ln(2)(mu(2)-OOCFc)(2)]; each Ln(III) ion has an irregular polyhedral coordination environment with nine coordinated oxygen atoms derived from the ferrocenecarboxylate ligands and coordinated solvent molecules. In the solid-state structure of compound 1, [Gd-2(mu(2)-OOCFc)(2)(OOCFC)(4)(MeOH)(2)(H2O)(2)] groups are joined together by hydrogen bonds forming a two-dimensional network. Both compounds 2 and 3 show one-dimensional chain structures by hydrogen bonding; they are different from 1. Magnetic measurements show unexpected ferromagnetic coupling between the gadolinium(III) ions; the best fittings to the experimental magnetic susceptibilities gave J = 0.006 cm(-1) and g = 2.0 for 1. The magnetic behavior for 2 was also studied in the temperature range of 1.8-300 K.