New porous lanthanide-organic frameworks: Synthesis, characterization, and properties of lanthanide 2,6-naphthalenedicarboxylates

Three porous, 3-D coordination polymers [Pr-4(NDC)(6)(H2O)(6)].2H(2)O (1), [Eu-4(NDC)(6)(H2O)(5)].3H(2)O (2) and [Yb-2(NDC)(3)(H2O)].H2O (3) based on lanthanide 2,6-naphthalenedicarboxylates (NDC) were synthesized by hydrothermal reactions of lanthanide chlorides with NDC and their properties were investigated. Polymers 1, 2 and 3 differ in the coordination environment of the Ln(III) ions. Their 3-D networks are reminiscent of the shape of a compressed honeycomb, showing 1-D open channels. The guest water molecules and coordinating water molecules are enclathrated in the channels. The photophysical properties of the EU3+ complex were investigated by high-resolution luminescence spectroscopy. The results indicate that there are four Eu-III ion sites in complex 2, which is in accordance with the results of the single-crystal X-ray diffraction studies. Thermogravimetric and variable -temperature powder X-ray diffraction analyses show that the porous frameworks of this series of complexes are relatively stable. The framework remained even when the guest molecules were lost and did not collapse until the temperature reached 430 degreesC. The magnetic properties of 2 were also investigated. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.