Complex three-dimensional lanthanide metal-organic frameworks with variable coordination spheres based on pyrazine-2,3,5,6-tetracarboxylateElectronic supplementary information (ESI) available: TGA curves, FTIR spectra, PXRD patterns, and the lists of bond lengths, bond angles and other structural details are provided as ESI. Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center as CCDC no. 1035324 and 1035325 for 1 and 2 respectivel

Metal-organic frameworks {[Ln 4 (pztc) 3 (H 2 O) 11 ]·10(H 2 O)} n (Ln = Gd( 1 ), Tb( 2 ); pztc = pyrazine-2,3,5,6-tetracarboxylate) 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 Ln( iii ) 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 Ln( iii ) ions and these are octa- and nona-coordinate centers, with irregular coordination polyhedra from [Ln(pztc) 2 (H 2 O) 6 ], [Ln(pztc) 2 (H 2 O) 4 ], [Ln(pztc) 3 (H 2 O) 3 ], [Ln(pztc) 3 (H 2 O)], and [Ln(pztc) 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. An open 3-D MOF with complex connectivity of multi-topic pyrazine-2,3,5,6-tetracarboxylate linker and Ln( iii ) ions.