Four New Cd(II) Coordination Polymers with Mixed Multidentate N‑Donors and Biphenyl-Based Polycarboxylate Ligands: Syntheses, Structures, and Photoluminescent Properties

Four new cadmium(II) coordination polymers (CPs), {[Cd(Hpptpd)(H2bptta)]·8H2O} n (1), {[Cd2(Hpptpd)2(bptta)(H2O)2]·4H2O} n (2), {[Cd2(pptpz)(bpta)(H2O)]·H2O} n (3), and {[Cd(Hpptpz)(bpba)]·2H2O} n (4) (Hpptpd = 2-(3-(4-(pyridin-4-yl)phenyl)-1H-1,2,4-triazol-5-yl)pyridine, Hpptpz = 2-(3-(4-(pyridin-4-yl)phenyl)-1H-1,2,4-triazol-5-yl)pyrazine, H4bptta = 3,3′,5,5′-biphenyltetracarboxylic acid, H3bpta = 3,4′,5-biphenyltricarboxylic acid, H2bpba = 3,4′-biphenylbicarboxylic acid), were synthesized under hydrothermal conditions. The CPs were structurally characterized by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), and thermogravimetric analyses (TGA). Complex 1 exhibits an unusual 2D + 2D → 2D parallel interpenetrated 63-hcb network. The adjacent 2D networks are interdigitated with each other to form the resulting three-dimensional (3D) supramolecular architecture through the interbilayer π···π stacking between Hpptpd ligands and nonclassical C–H···O hydrogen bonds. Complex 2 is a one-dimensional (1D) molecular ladder along the a direction and further extended via hydrogen bonds into the 3D supramolecular framework. Complex 3 exhibits a novel complicated 3D (3,4,4,5)-connected framework with the Schläfli symbol of (4·65)(4·67·82)(63)(64·82). Complex 4 manifests an intriguing layered structure with 5-connected cadmium atom as a unique node and can be simplified to an Archimedean (33·44·53) cem topology with triangular and rectangular circuits. The topology of 4 could be alternately simplified to a 3,4-connected binodal layer with a V2O5-type network. The thermal stabilities and photoluminescence behaviors of them were also discussed.