Isopolymolybdate-Based Cobalt/Nickel Coordination\nPolymers Constructed by V‑Type N‑Donor Ligands

Abstract

Four novel isopolymolybdate-based\ncoordination polymers (CPs),\nconstructed from 2,6-bis­(1,2,4-triazol-1-yl)­pyridine (btp), 1,3-bis­(4<i>H</i>-1,2,4-triazol-4-yl)­benzene (btb), and 3,5-bis­(1-imidazolium)­pyridine\n(bip), have been synthesized under a hydrothermal method: {[Co­(btp)­(H₂O)₂(β-Mo₈O₂₆)_0.5]·3H₂O}<i>_n</i> (<b>1</b>), [Ni­(btp)­(H₄Mo₆O₂₂)_0.5]_<i>n</i> (<b>2</b>), [Co­(btb)­(H₂O)­(β-Mo₈O₂₆)_0.5]_<i>n</i> (<b>3</b>), and {[Co­(Hbip)₂(H₂O)₂(γ-Mo₈O₂₆)]·6H₂O}<i>_n</i> (<b>4</b>). Complex <b>1</b> exhibits one 3D framework with an unexpected 3-nodal 2,4,6-c\nnet topology containing the 1D {β-Mo₈O₂₆}<i>_n</i> chains, 6-connected Co^II centers, and V-type coordinated btp ligands. The neighboring [Mo₆O₂₂]^4– anions of complex <b>2</b> are bridged by the Ni^II centers to build one\n2D {Ni₂(Mo₆O₂₂)} network, which is\narranged into the 3D framework through the weak π···π\nstacking interactions. In compound <b>3</b>, one 3D framework\nis formed by the adjacent 1D {Co₂(btp)₂}<i>_n</i> chains connected by {β-Mo₈O₂₆}_<i>n</i> units, which demonstrates\na rare 4,6-c fsc topology. In complex <b>4</b>, one 2D {Co­(Hbip)₂(γ-Mo₈O₂₆)} layer with a (4, 4)\nnetwork is connected to one 3D hydrogen-bonding framework <i>via</i> N-H···O and O-H···O hydrogen\nbonds. Magnetic data indicate that complexes <b>1</b> and <b>4</b> exhibit antiferromagnetic behaviors, whereas complexes <b>2</b> and <b>3</b> reveal spin-canting magnetic behavior\nand metamagnetic behavior, respectively. In addition, the proton conductivity\nof complexes <b>3</b> and <b>4</b> was investigated, showing\nthat compound <b>4</b> has good proton conductivity at 85 °C\nand a relative humidity of 98% RH.