A new three-dimensional twofold interpenetrated cadmium(II) metal-organic framework: synthesis, structure and photoluminescence properties.

The design and synthesis of metal-organic frameworks (MOFs) have attracted much interest due to the aesthetics of their crystalline architectures and their potential applications as new functional materials. A new twofold interpenetrated three-dimensional (3D) MOF, namely, poly[[triaqua(μ-(2R,2'R)-2,2'-{[1,4-phenylenebis(carbonyl)]bis(azanediyl)}dipropionato-κO:O,O:O:O,O,O)(μ-(2R,2'R)-2,2'-{[1,4-phenylenebis(carbonyl)]bis(azanediyl)}dipropionato-κO:O:O)dicadmium(II)] dihydrate], {[Cd(CHNO)(HO)]·2HO}, (I), has been synthesized by the reaction of Cd(CHCOO)·2HO with the synthesized ligand (2R,2'R)-2,2'-{[1,4-phenylenebis(carbonyl)]bis(azanediyl)}dipropionic acid (HL). Single-crystal X-ray diffraction analysis reveals that the carboxylate groups from two crystallographically independent L dianions link the cadmium cations into a one-dimensional helical secondary building unit (SBU). The resulting SBUs are extended into a 3D metal-organic framework via the terephthalamide moiety of the ligand as a spacer. In the crystal, two independent MOFs interpenetrate each other, thus producing a twofold interpenetrated 3D architecture, which shows an unprecedented 2-nodal (7,9)-connected net with the point (Schläfli) symbol (3·4·5)(3·4·5·6). MOF (I) was further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction and thermogravimetric analysis. The photoluminescence properties and UV-Vis absorption spectrum of (I) have also been investigated. The MOF exhibits enhanced fluorescence emission with a high photoluminescence quantum yield of 31.55% and a longer lifetime compared with free HL.