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)(H 2 bptta)]·8H 2 O} n ( 1 ), {[Cd 2 (Hpptpd) 2 (bptta)(H 2 O) 2 ]·4H 2 O} n ( 2 ), {[Cd 2 (pptpz)(bpta)(H 2 O)]·H 2 O} n ( 3 ), and {[Cd(Hpptpz)(bpba)]·2H 2 O} n ( 4 ) (Hpptpd = 2-(3-(4-(pyridin-4-yl)phenyl)-1 H -1,2,4-triazol-5-yl)pyridine, Hpptpz = 2-(3-(4-(pyridin-4-yl)phenyl)-1 H -1,2,4-triazol-5-yl)pyrazine, H 4 bptta = 3,3′,5,5′-biphenyltetracarboxylic acid, H 3 bpta = 3,4′,5-biphenyltricarboxylic acid, H 2 bpba = 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 6 3 - 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 (4·6 5 )(4·6 7 ·8 2 )(6 3 )(6 4 ·8 2 ). Complex 4 manifests an intriguing layered structure with 5-connected cadmium atom as a unique node and can be simplified to an Archimedean (3 3 ·4 4 ·5 3 ) cem topology with triangular and rectangular circuits. The topology of 4 could be alternately simplified to a 3,4-connected binodal layer with a V 2 O 5 -type network. The thermal stabilities and photoluminescence behaviors of them were also discussed.