Structures of incommensurate and commensurate composite crystals RbₓMnO₂(x = 1.3711, 1.3636)

Titelangaben

Nuss, Jürgen ; Pfeiffer, Steffen ; van Smaalen, Sander ; Jansen, Martin:
Structures of incommensurate and commensurate composite crystals RbₓMnO₂(x = 1.3711, 1.3636).
In: Acta Crystallographica Section B. Bd. 66 (2010) Heft 1 . - S. 27-33.
ISSN 2052-5206
DOI: https://doi.org/10.1107/S0108768109053312

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Abstract

Rb₁.₃₇₁₁MnO₂(Rb₁₁Mn₈O₁₆) has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors Mn₂O₃, RbNO₃ and RbN₃. The structure of this extremely air- and moisture-sensitive compound can best be described in terms of an incommensurate composite structure, built up by a honeycomb-like framework of Rb ions, as one subsystem and by a second subsystem of chains, consisting of edge-sharing MnO₄/₂ tetrahedra. These two composite substructures interpenetrate in such a way that the manganate chain polyanions centre the channels of the Rb-honeycomb framework. Crystals transform by an aging process into Rb₁.₃₆₃₆MnO₂ (Rb₁₅Mn₁₁O₂₂), which has a similar structure but a different commensurate modulation. Two reasons can be established for the origin of the modulations: the charge ordering of Mn²⁺Mn³⁺ on one hand, and the incompatibility of the Mn—-Mn and Rb—-Rb separations on the other.