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)]­·CH3CN}n (1), {[Cu­(CA)­(H2O)2]·H2O}n (2), and [Ag2(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 (4·62)2­(42·610·83) Schlafli
topology based on binuclear secondary building units equivalent to
a paddle wheel. Compound 2 features a (3,3)-connected
two-dimensional (2D) fes (4·82) layer,
which is further extended to a 3D supramolecular network by interlayer
hydrogen bonds. Compound 3 is a rare 3D framework with
a (46)2(49·618·8)
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 (ε′
= 321), which is considered to be one of the best among crystalline
porous coordination polymers within the nonpolar point group.