Ultramicroporous channel lanthanide coordination polymers of 2,5-pyrazinedicarboxylate

Five lanthanide coordination polymers with composition {[Ln(pzdc)1.5(H2O)3] · 0.5H2O}∞, (Ln = Pr, 1; Nd, 2; Sm, 3; Eu, 4; Gd, 5; pzdc = 2,5-pyrazinedicarboxylate), have been synthesized by reacting Ln(NO3)3 · 6H2O with 2,5-pyrazinedicarboxylic acid under hydrothermal condition in the absence of additional base and characterized by elemental analysis, IR spectra and TG analysis, as well as single-crystal X-ray diffraction. They crystallize isostructurally in the triclinic space group P-1 and the cell parameters agree with the ionic radii of the Ln(III) ions. Each trivalent rare earth ion is nine coordinate in an N2O7 environment. The ligand 2,5-pyrazinedicarboxylate adopts three coordination modes, through which the lanthanide ions are linked together to form an infinite three dimensional structure. A 1D channel exists along the (1 0 0) direction which accommodates uncoordinated water by hydrogen bonds. Heating of 4 at 120 °C evacuated the uncoordinated water while retaining its single crystallinity with only minor change in cell parameters (crystal 6, [Eu(pzdc)1.5(H2O)3]∞). This hydrophilic ultramicroporous channel is selective to accommodate water only among common solvents, which has some potential interest for solvent separation.