pH-Dependent Binary Metal−Organic Compounds Assembled from Different Helical Units: Structural Variation and Supramolecular Isomers

Six binary metal−organic compounds, namely, [Cd(L)2] (1), α-[Cd(L)2(H2O)] (2), β-[Cd(L)2(H2O)] (3a and 3b), γ-[Cd(L)2(H2O)] (4), and [Cd(L)2(H2O)2] (5), where HL = 4-(pyridin-3-ylmethoxy)benzoic acid, have been synthesized under hydrothermal conditions. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. The structure of 1 is a two-dimensional (2D) → 2D 3-fold parallel interpenetrating network with (4,4) grid. Compounds 2, 3, and 4 are supramolecular isomers formed by Cd(II) cations, L− ligand, and water molecule, showing a 2D → 2D 2-fold parallel interpenetrating (4,4) network for 2, single (4,4) network for 3a and 3b, and (66) topological net for 4 through using different reaction materials. Compounds 3a and 3b show chiral structures by spontaneous resolution using an achiral ligand. In compound 5, Cd(II) cations are linked by L− ligands to form an infinite chain. Comparing these structures, the number of coordination water molecules, the coordination fashion of organic ligands, and reaction conditions play fundamental roles in the formation of the final products. In addition, the luminescent properties of these compounds are discussed.