Isopolymolybdate-Based Cobalt/Nickel Coordination Polymers Constructed by V-Type N-Donor Ligands

Abstract

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