The self-assembly of 4-hydroxypyridine-2,6-dicarboxylic acid (H(3)CAM) and pyridine-2,6-dicarboxylic acid (H(2)PDA) with Zn(II) salts under hydrothermal conditions gave two novel coordination polymers {[Zn(HCAM)]center dot H2O}(n) (1) and {[Zn(PDA)(H2O)(1.5)]}(n) (1a). 1 and 1a comprise of a 2D (4,4) net and a 1D zigzag chain, respectively, in which a new coordination mode of PDA is found. The reactions of H(3)CAM and H(2)PDA with Nd2O3 in the M/L ratio 2:3 gave {[Nd-2(HCAM)(3)(H2O)(4)], 2H(2)O}(n) (2) and {[Nd-2(PDA)(3)(H2O)(3)]center dot 0.5H(2)O}(n) (2a). In 2, a square motif as a building block constructed by four Nd(III) ions was further assembled into a highly ordered 2D (4,4) grid. 2a is a 3D microporous coordination polymer. It is interesting to note that, when Ln(III) salts rather than oxides were employed, the reaction produced {[Ln(CAM)(H2O)(3)]center dot H2O}(n) (Ln = Gd, 3; Dy, 4; Er, 5) for H(3)CAM and {[Gd-2(PDA)(3)(H2O)(3)]center dot H2O}(n) (3a) for H2PDA. 3-5 are 2D coordination polymers with a 3(3)4(2) uniform net, where hydroxyl groups of H(3)CAM coordinate with metal ions. The reaction of H(3)CAM and Er2O3 instead of Er(ClO4)(3) produced {[Er-2(HCAM)(3)(H2O)(4)]center dot 2H(2)O}(n) (6). The compounds 2a and 3a, 2 and 6 are isomorphous. The stereochemical and supramolecular effects of hydroxyl groups result in the dramatic structural changes from 1D (1a) to 2D (1) and from 2D (2) to 3D (2a). When Ln(III) salts instead of Ln(2)O(3) were employed in the hydrothermal reactions with H(3)CAM, different self-assembly processes gave the products of different metal/ligand ratio with reactants (3-5).