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

Hisashi Ōkawa; Masaaki Sadakiyo; Kazuya Otsubo; Ko Yoneda; Teppei Yamada; Masaaki Ohba; Hiroshi Kitagawa

doi:10.1021/acs.inorgchem.5b01176

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

Inorg Chem. 2015 Sep 8;54(17):8529-35. doi: 10.1021/acs.inorgchem.5b01176. Epub 2015 Aug 17.

Authors

Hisashi Ōkawa^{1

2}, Masaaki Sadakiyo³, Kazuya Otsubo^{3

2}, Ko Yoneda¹, Teppei Yamada³, Masaaki Ohba^{1

2}, Hiroshi Kitagawa^{3

2}

Affiliations

¹ Department of Chemistry, Faculty of Science, Kyushu University , Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan.
² Core Research for Evolutional Science and Technology, Japan Science and Technology Agency , Gobancho 7, Chiyoda-ku, Tokyo 102-0076, Japan.
³ Division of Chemistry, Graduate School of Science, Kyoto University , Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan.

PMID: 26280936
DOI: 10.1021/acs.inorgchem.5b01176

Abstract

Proton conduction of the La(III)M(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(III)Co(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.