Rietveld refinement of a triclinic structure for synthetic Na-birnessite using synchrotron powder diffraction data

Rietveld refinement using synchrotron powder X-ray diffraction data revealed that the crystal structure of synthetic Na-birnessite is triclinic (C 1 ), not monoclinic as was previously reported. The Mn–O octahedra have elongated axial bonds, consistent with Jahn–Teller distortion resulting from partial occupancy by Mn 3+ . Mean Mn–O distances indicate that Mn sites are ∼2/3 Mn 4+ and ∼1/3 Mn 3+ . The interlayer Na cations and H 2 O molecules occupy a split site that shows evidence of considerable disorder.