Construction of Four γ-Octamolybdate-Based Coordination Polymers Using Linear Nitrogen Heterocyclic Ligands for Proton Conduction

POM-based coordination polymers are emerging as promising crystalline materials for proton conduction. Herein, we successfully synthesized four new γ-octamolybdate-based coordination polymers using the linear nitrogen heterocyclic ligand 1-(4H-1,2,4-triazole-4-yl)-4-(imidazole-1-yl) (benzene [tib]), which are designated as {[Co(Htib)2(Mo8O26)(H2O)2]·4H2O}n (1), {Zn2(tib)3(H2O)4(Mo8O26)]·6H2O}n (2), {[Ni2(tib)3(H2O)6(Mo8O26)]·2H2O}n (3), and {[Cu4(tib)2(H2O)4(Mo8O28)]·2H2O}n (4). Due to the diverse connection modes of γ-octamolybdate and tib ligand to metal ions, the dimensionalities of their structures vary from 1D and 2D to 3D. Compound 1 exhibits a 1D chain structure, with γ-{Mo8O26} sandwiched between Co(tib)2 units, while compound 2 develops into a 2D layered structure through the linkage of {Zn2Mo8O26} units with μ2-tib ligands. Compounds 3 and 4 display 3D structures, where the former is constructed from 1D {Mo8O26}n chains and Ni2(tib)2 units and the latter is formed by linking tib ligands to adjacent 2D layers, which are composed of the distinctive {Mo8O28} units and CuII ions. Moreover, abundant hydrogen bonds are present in four compounds, which is beneficial for proton transport. The proton conductivity values of compounds 1–4 are 6.10 × 10–4, 5.68 × 10–4, 6.14 × 10–4, and 1.30 × 10–3 S cm–1 at 98% RH and 358 K, respectively.