Structural Diversity and Dimensionality of Three Cu(II)-dpds-C5O52– Coordination Polymers Controlled by the Coordination Sphere of Cu(II) Centers and the Coordination Modes of C5O52– (dpds = 4,4′-Dipyridyldisulfide)

Three supramolecular architectures, [Cu₂(dpds)₂(C₅O₅)₂(H₂O)₄]·3H₂O (1), [Cu(dpds)(C₅O₅)]·3H₂O (2), and [Cu₂(dpds)₂(C₅O₅)₂]·9H₂O·C₂H₅OH (3) (dpds = 4,4'-dipyridyldisulfide and C₅O₅ ^2- (croconate) = dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione), have been synthesized and structurally characterized. Compound 1 contains two crystallographically independent Cu(II) ions, which are both distorted octahedral geometry with elongation along the croconate- and H₂O-bound axial positions and bonded with two N atoms of two dpds, two O atoms of one C₅O₅ ^2-, and two H₂O molecules. Two crystallographically independent dpds ligands, both adopting the bis-monodentate bridging mode, connect two Cu(II) ions to form a one-dimensional zigzag chain-like coordination polymer. In 2 and 3, there are two and three crystallographically independent Cu(II) ions, respectively, which are all distorted octahedral geometries with elongation along the croconate-bound axial positions six-coordinated and bonded with two N atoms of two dpds ligands in cis- or/and trans-forms and four O atoms of two C₅O₅ ^2- ligands. The dpds ligands in 2 and 3 all adopt the bis-monodentate bridging mode, and the C₅O₅ ^2- ligands act as bridging ligands with bridging bis-bidentate through three C₅O₅ ^2- oxygen atoms in 2 and bridging bis-bidentate through four adjacent C₅O₅ ^2- oxygen atoms in 3, respectively, linking the Cu(II) ions to generate a two-dimensional layered and a three-dimensional metal-organic framework, respectively. The structural diversity and dimensionality observed in 1-3 may be attributed to the cis- or/and trans-coordination sphere of Cu(II) centers with two dpds ligands and the coordination modes of croconate ligands. Thermal stability and in situ temperature-dependent structural variations of 1-3 have been verified by thermogravimetric analysis and powder X-ray diffraction measurements. Compounds 1 and 3 both exhibit water vapor capture behaviors with hysteresis isotherms.