Proton Conduction Study on Water Confined in Channel or Layer Networks of La^IIIM^III(ox)₃·10H₂O (M = Cr, Co, Ru, La)

(Chemical Equation Presented). Proton conduction of the La^IIIM^III compounds, LaM(ox)₃·10H₂O (abbreviated to LaM; M = Cr, Co, Ru, La; ox^2- = oxalate) is studied in view of their networks. LaCr and LaCo have a ladder structure, and the ladders are woven to form a channel network. LaRu and LaLa have a honeycomb sheet structure, and the sheets are combined to form a layer network. The occurrence of these structures is explained by the rigidness versus flexibility of [M(ox)₃]^3- in the framework with large La^III. The channel networks of LaCr and LaCo show a remarkably high proton conductivity, in the range from 1 × 10^-6 to 1 × 10^-5 S cm^-1 over 40-95% relative humidity (RH) at 298 K, whereas the layer networks of LaCr and LaCo show a lower proton conductivity, ∼3 × 10^-8 S cm^-1 (40-95% RH, 298 K). Activation energy measurements demonstrate that the channels filled with water molecules serve as efficient pathways for proton transport. LaCo was gradually converted to La^IIICo^II(ox)_2.5·4H₂O, which had no channel structure and exhibited a low proton conductivity of less than 1 × 10^-10 S cm^-1. The conduction-network correlation of LaCo(ox)_2.5·4H₂O is reported.