Homometallic europium(III) and terbium(III) trans-2-butenoate polymers, chemical formulas [{Eu₃(MeCH=CHCO₂)₉(H₂O)₄}·H₂O·EtOH]_n (1) and [{Tb(MeCH=CHCO₂)₃(H₂O)}·MeCH=CHCO₂H]_n (2) and their dimeric 1,10-phenanthroline derivatives [Ln₂(MeCH=CHCO₂)₆(phen)₂]·2H₂O, with Ln=Eu (3) and Tb (4), were prepared and characterized by single-crystal X-ray diffraction. The coordination polymers 1 and 2 adopt different carboxylate-bridged infinite chain structures. While the europium compound 1 shows three independent europium centers linked to each other by three different types and number of carboxylate bridges, the terbium polymer 2 shows one independent metal center bridged by the same type of double carboxylates along the chains. Compounds 3 and 4 are isomorphous dinuclear structures with quadruply bridged carboxylate groups, two in the η¹:η¹:μ₂ and two in the η²:η¹:μ₂ modes. The magnetic and photophysical behaviors of the four compounds are reported in the solid state.