title: The tunnel manganese oxide Na4.32Mn9O18: a new Na+ site discovered by single-crystal X-ray diffraction.
abstract: The title compound, tetrasodium nonamanganese octadecaoxide, Na(4.32)Mn(9)O(18), was synthesized by reacting Mn(2)O(3) with NaCl. One Mn atom occupies a site of 2/m symmetry, while all other atoms sit on mirror planes. The compound is isostructural with Na(4)Ti(4)Mn(5)O(18) and suggestive of Mn(3+)/Mn(4+) charge ordering. It has a double-tunnel structure built up from double and triple chains of MnO(6) octahedra and single chains of MnO(5) square pyramids by corner sharing. Disordered Na(+) cations occupy four crystallographic sites within the tunnels, including an unexpected new Na(+) site discovered inside the large S-shaped tunnel. A local-ordering model is used to show the possible Na(+) distribution, and the unit-cell evolution during charging/discharging is explained on the basis of this local-ordering model.
authors.affiliation: State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, People's Republic of China.
authors.forename: Qingxin
authors.initials: Q
authors.lastname: Chu
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Wang
authors.forename: Qiliang
authors.initials: Q
authors.lastname: Li
authors.forename: Xiaoyang
authors.initials: X
authors.lastname: Liu