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

Proton conduction of the La(III)Mi(III) compounds, LaM(ox)(3)center dot 10H(2)O (abbreviated to Lan(j) 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 x 10(-6) to 1 x 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, similar to 3 x 10(-8) S cm(-1) (4095% 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 (LaCoII)-Co-III(ox)(2.5)center dot 4H(2)O, which had no channel structure and exhibited a low proton conductivity of less than 1 x 10(-1) S cm(-1). The conduction-network correlation of LaCo(ox)(2.5)-4H(2)O is reported.