A novel lanthanide metal-organic framework was yielded by hydrothermal reaction of 5-chloro-6-hydroxypyridine-3-carboxylic acid (5-Cl-6-HOPy-3-CO2H) and Dy2O3 in the presence of oxalic acid (H2OX), namely, [Dy2(1H-5-Cl-6-Opy-3-CO2)2(OX)2(H2O)]·2H2O (1, 1H-5-Cl-6-Opy-3-CO2－ = 1-hydro-5-chloro-6-oxopyridine-3-carboxylate). The new ligand 1H-5-Cl-6-Opy-3-CO2－ was formed by the autoisomerization of single deprotonated 1H-5-Cl-6-HOpy-3-CO2－ anion (from the enol form into the ketone one). There exist two types of dysprosium(III) ions in (1, showing two different coordination configurations. The dysprosium(III) ions are bridged by oxalate anions to construct an interesting layer network with a 4-nodal (3,5)-connected topology (32.52)(3.53), such layers are further connected with each other by the bridging ligand 1H-5-Cl-6-HOpy-3-CO2－ to complete the three-dimensional(3D) framework structure. Magnetic investigations indicated that (1 is a field-induced single-molecule magnet, displaying a two-step slow magnetic relaxation process, with an effective thermal barrier of 37.6 K. Surprisingly, a zigzag chain-like gadolinium(III) complex, [Gd(1H-5-Cl-6-Opy-3-CO2)2(OX)0.5(H2O)3]·6 H2O (2), was isolated using Gd2O3 instead of Dy2O3, propably owing to the lanthanide contraction effect. Notebaly, an amazing (H2O)6 supramolecular aggregate with a unique F shape exists in the crystal structure of (2).