Towards a unified description of the AMOB2O5 (A=K, Rb, Cs, Tl; M=Nb, Ta) family of compounds.
Single-crystal X-ray diffraction data (Mo Kalpha radiation) are used to re-refine the structure of RbNbOB2O5, rubidium niobium oxo pyroborate. The structure is refined as an incommensurate modulated structure with superspace group symmetry Pmn2(1)(0,0.4,0)s and lattice parameters a = 7.406 (2), b = 3.939 (2) and c = 9.475 (2) A. Refinement on 3242 unique reflections converged to R = 0.031, while a previous conventional superstructure refinement led to R = 0.090. This lowering of the R factor goes hand-in-hand with a substantial reduction in the number of refined parameters. The refinement strongly suggests that the structure is effectively incommensurately modulated, despite an apparently rational magnitude of the primary modulation wave-vector and overlap of satellite reflections.
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Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia. schmid@rsc.anu.edu.au
Withers
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Corker
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Baules
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