Metal-organic frameworks {[Ln 4 IJpztc) 3 IJH 2 O) 11 ]·10IJH 2 O)} n (Ln = GdIJ1), TbIJ2); pztc = pyrazine-2,3,5,6tetracarboxylate) containing variable coordination spheres and with a complex and unusual three dimensional structure, were synthesized by the reaction of H 4 pztc with the respective LnIJIII) salt in water under hydrothermal conditions. The compounds were characterized by single crystal X-ray crystallography, elemental and thermal analysis, and FTIR spectroscopy. The asymmetric units in these compounds have four symmetry-independent LnIJIII) ions and these are octa-and nona-coordinate centers, with irregular coordination polyhedra from ijLnIJpztc) 2 IJH 2 O) 6 ], ijLnIJpztc) 2 IJH 2 O) 4 ], ijLnIJpztc) 3 IJH 2 O) 3 ], ijLnIJpztc) 3 IJH 2 O)], and ijLnIJpztc) 4 ] cluster units. The fully deprotonated ligand, pztc, coordinates to the Ln 3+ ions through seven or through ten of its atoms (i.e., the maximum coordination number for this ligand). The three-dimensional open framework contains irregular channels along the [001] crystallographic direction. The channels are approximately 12 Å wide at their largest dimension and contain strongly hydrogen bonded water molecules of crystallization which further stabilize the structure. The solvent accessible volume is 20% of the total volume. The structures exhibit magnetic behavior that is characteristic of the respective isolated paramagnetic lanthanide ions. CrystEngCommThis journal is