Synthesis, structure, magnetism and proton conductivity of a cyanide-bridged NiIICoIII framework

Abstract

A two-dimensional cyanide-bridged NiIICoIII coordination polymer, {[Ni(cyclam)]3[Co(CN)6]2·16H2O}n (1, cyclam = 1,4,8,11-tetraazacyclotetradecane), was constructed from hexacyanidocobaltate(III) anions, cyclam ligands and Ni2+ ions. Single-crystal X-ray structural analysis revealed that the [Ni(cyclam)]2+ species were bridged by [Co(CN)6]3- building units, leading to a 2D honeycomb topological structure. Interestingly, 1D microporous channels within the framework were formed with guest water molecules located. An N2 adsorption experiment supports the porosity of the compound. Magnetic investigations reveal the easy-axis magnetic anisotropy of the distorted octahedral Ni2+ ions in 1. However, no single-ion magnet behavior was observed. Due to the presence of significant hydrogen-bonded water channels, temperature- and humidity-dependent proton conduction behavior was observed in 1. The electrical conductivity reaches 2.9 × 10−4 S cm−1 at 44 °C and 100 % relative humidity. The forgoing results provide a relatively rare porous cyanide-bridged magnetic framework with proton conduction behavior. Additionally, this compound also highlights that cyanide-bridged frameworks are a potential great platform for the development of high-performance proton-conducting materials.