Cu- and Ag-Based Metal Organic Frameworks with 4-Pyranone-2,6-dicarboxylic Acid: Syntheses, Crystal Structures, and Dielectric Properties

Three Cu- and Ag-based metal-organic frameworks (MOFs) with different crystal structures from the same ligand CA (CA = 4-pyranone-2,6-dicarboxylic acid), {[Cu(CA)]center dot CH3CN}(n) (1), {[Cu(CA)(H2O)(2)]center dot H2O}(n) (2), and [Ag-2(CA)](n) (3) have been synthesized under solovthermal conditions. Crystal structures of all the compounds possessing the same crystal nonpolar point group of 2/m were determined by single-crystal X-ray diffraction analysis. Compound 1 has a (3,6)-connected three-dimensional (3D) rtl framework with (4.6(2))(2)(4(2).6(10).8(3)) Schlafli topology based on binuclear secondary building units equivalent to a paddle wheel. Compound 2 features a (3,3)-connected two-dimensional (2D) fes (4.8(2)) layer, which is further extended to a 3D supramolecular network by interlayer hydrogen bonds. Compound 3 is a rare 3D framework with a (4(6))(2)(4(9).6(18).8) topological symbol without solvent molecules, which contains three rings that are 14-member, 10-member, and 8-member, respectively. Moreover, the dielectric properties and mechanisms of these MOFs have been measured at various frequencies and temperatures, while compound 3 possesses a relatively large dielectric constant (epsilon' = 321), which is considered to be one of the best among crystalline porous coordination polymers within the nonpolar point group.