The hydrothermal reaction of Ln(2)O(3) (Ln = Er, Gd, and Sm), pyridine-2,5-dicarboxylic acid (H(2)Pydc), and Cu(II) reagents (CuO, Cu(OAc)(2).2H(2)O, or CuCl2.2H(2)O) with a mole ratio of 1:2:4 resulted in the formation of six polymeric Cu(II)-Ln(III) complexes, [{Ln(2).Cu-3(pydc)(6)(H2O)(12)}.4H(2)O](n) (Ln = Er (1); Ln = Gd (2)), [{Ln(4)CU(2)(pydc)(8)(H2O)(12)}.4H(2)O](n) (Ln = Sm (3); Ln = Gd (4); Ln = Er (5)), and [{Gd2Cu2(pydc)(4)(H2O)(8)}.Cu(pydc)(2).12H(2)O](n) (6). 1 and 2 are isomorphous and crystallize in triclinic space group P1. Compounds 3-5 are isomorphous and crystallize in monoclinic space group P2(1)/c. Compound 6 crystallizes in triclinic space group PT. Complexes 1 and 2 have one-dimensional zigzag chain structures and compounds 3-5 display three-dimensional wavelike polymeria structures, while 6 has an infinite sandwich-type structure. The different structures of the complexes are induced by the different forms of Cu(II) reagents; the reactions of Cu(OAc)(2).2H(2)O yield high Cu/Ln ratio products 1, 2, and 6, while the reactions of CuO or CuCl.2H(2)O/2,2'-bipyridine results in low Cu/Ln ratio compounds 3-5. Temperature-dependent magnetic susceptibilities for 2, 4, and 5 were, studied, and the thermal stabilities of complexes 2 and 4 were examined.