Three isostructural Cu₂Ln₂ 1-D polymers [Cu₂Ln₂L₁₀(H₂O)₄·3H₂O]_n where Ln = Gd (1), Er (2), and Y (3) and HL= trans-2-butenoic acid, were synthesized and characterized by X-ray crystallography, electron paramagnetic resonance, and magnetic measurements. Pairs of alternate Cu₂ and Ln₂ dinuclear units are combined into a linear array by a set of one covalent η²:η¹:η₂ carboxylate oxygen and two H bonds, at Cu⋯Ln distances of ca. 4.5 Å. These units exhibit four η¹:η¹:η₂ and two η²:η¹:η₂ carboxylate bridges, respectively. Magnetic measurements between 2 and 300 K, fields B₀ = μ₀H between 0 and 9 T, and electron paramagnetic resonance (EPR) measurements at the X-band and room temperature are reported. The magnetic susceptibilities indicate bulk antiferromagnetic behavior of the three compounds at low temperatures. Magnetization and EPR data for 1 and 3 allowed evaluation of the exchange couplings between both Cu and Gd ions in their dinuclear units and between Cu and Gd neighbor ions in the spin chains. The data for the isolated Cu₂ units in 3 yield g_|| = 2.350 and g_T = 2.054, J_Cu-Cu = -338 (3) cm^-1 for the exchange coupling [H_ex(1,2) = -J_1-2 S₁·S₂], and D₀ = -0.342 (0.003) cm^-1 and E₀ = 0.003 (0.001) cm^-1 for the zero-field-splitting parameters of the triplet state arising from anisotropic spin-spin interactions. Considering tetranuclear blocks Gd-Cu-Cu-Gd in 1, with the parameters for the Cu₂ unit obtained for 3, we evaluated ferromagnetic interactions between Cu and Gd neighbors, J_Cu-Gd = 13.0 (0.1) cm^-1, and between Gd ions in the Gd₂ units, J_Gd-Gd = 0.25 (0.02) cm^-1, with g_Gd = 1.991. The bulk antiferromagnetic behavior of 1 is a consequence of the antiferromagnetic coupling between Cu ions and of the magnitude, |J_Cu-Gd|, of the Cu-Gd exchange coupling. Compound 2 displays a susceptibility peak at 15 K that may be interpreted as the combined result from antiferromagnetic couplings between Er^III ions in Er₂ units and their coupling with the Cu₂ units.