Dehydration-Triggered Charge Transfer and High Proton Conductivity in (H₃O)[Ni^III(cyclam)][M^II(CN)₆] (M = Ru, Os) Cyanide-Bridged Chains

The coexistence of dehydration-driven charge transfer, magnetic interactions, and high proton conductivity was found in two bimetallic alternating CN-bridged chains {(H₃O)­[Ni^III(cyclam)]­[M^II(CN)₆]·5H₂O}_n (M = Ru (1), Os (2); cyclam = 1,4,8,11-tetraazacyclotetradecane). Dehydration of these materials causes structural transformation and triggers charge transfer between the metal centers: Ni^III–NC–M^II → Ni^II–NC–M^III. The CT process, whose extent is tuned by the change of the anionic building block, causes significant increase of magnetic moment, appearance of antiferromagnetic interactions, and noticeable changes in color. The high conductivity values of σ = 1.09 × 10^–3 (1) and 1.12 × 10^–3 S cm^–1 (2) at 295 K and 100% relative humidity allow the classification of the materials as superionic conductors. The proton conduction occurs according to the Grotthuss mechanism as a hopping of protons between H-bonded water molecules due to the presence of the H₃O⁺ ions, which compensate negative charge of the coordination chains.