Four New Cd(II) Coordination\nPolymers with Mixed Multidentate\nN‑Donors and Biphenyl-Based Polycarboxylate Ligands: Syntheses,\nStructures, and Photoluminescent Properties

Abstract

Four new cadmium­(II) coordination polymers (CPs), {[Cd­(Hpptpd)­(H₂bptta)]·8H₂O}_<i>n</i> (<b>1</b>), {[Cd₂(Hpptpd)₂(bptta)­(H₂O)₂]·4H₂O}_<i>n</i> (<b>2</b>), {[Cd₂(pptpz)­(bpta)­(H₂O)]·H₂O}<i>_n</i> (<b>3</b>), and {[Cd­(Hpptpz)­(bpba)]·2H₂O}_<i>n</i> (<b>4</b>) (Hpptpd = 2-(3-(4-(pyridin-4-yl)­phenyl)-1<i>H</i>-1,2,4-triazol-5-yl)­pyridine, Hpptpz = 2-(3-(4-(pyridin-4-yl)­phenyl)-1<i>H</i>-1,2,4-triazol-5-yl)­pyrazine, H₄bptta = 3,3′,5,5′-biphenyltetracarboxylic\nacid, H₃bpta = 3,4′,5-biphenyltricarboxylic acid,\nH₂bpba = 3,4′-biphenylbicarboxylic acid), were synthesized\nunder hydrothermal conditions. The CPs were structurally characterized\nby single-crystal X-ray diffraction analyses and further characterized\nby infrared spectra (IR), elemental analyses, powder X-ray diffraction\n(PXRD), and thermogravimetric analyses (TGA). Complex <b>1</b> exhibits an unusual 2D + 2D → 2D parallel interpenetrated\n6³-<b>hcb</b> network. The adjacent 2D networks are\ninterdigitated with each other to form the resulting three-dimensional\n(3D) supramolecular architecture through the interbilayer π···π\nstacking between Hpptpd ligands and nonclassical C–H···O\nhydrogen bonds. Complex <b>2</b> is a one-dimensional (1D) molecular\nladder along the <i>a</i> direction and further extended\nvia hydrogen bonds into the 3D supramolecular framework. Complex <b>3</b> exhibits a novel complicated 3D (3,4,4,5)-connected framework\nwith the Schläfli symbol of (4·6⁵)­(4·6⁷·8²)­(6³)­(6⁴·8²). Complex <b>4</b> manifests an intriguing layered\nstructure with 5-connected cadmium atom as a unique node and can be\nsimplified to an Archimedean (3³·4⁴·5³) <b>cem</b> topology with triangular and rectangular\ncircuits. The topology of <b>4</b> could be alternately simplified\nto a 3,4-connected binodal layer with a V₂O₅-type network. The thermal stabilities and photoluminescence behaviors\nof them were also discussed.