Hydrogen Bonding and Jahn–Teller Distortion in Groutite,α-MnOOH, and Manganite,γ-MnOOH, and Their Relations to the Manganese Dioxides Ramsdellite and Pyrolusite

✍ Scribed by Thomas Kohler; Thomas Armbruster; Eugen Libowitzky

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 596 KB
• Volume: 133
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7516

✦ Synopsis

Kalahari manganese field (South Africa), were refined including hydrogen positions from room temperature X-ray single-crystal data. The refinements converged to R values of 1.5% for 479 (groutite) and of 2.0% for 821 (manganite) unique reflections, respectively. A (101) twin refinement based on F 2 obs was applied for manganite leading to a twin contribution of ca. 0.9 : 0.1. The structures of groutite and manganite are distorted derivatives of the MnO 2 polymorphs ramsdellite and pyrolusite (rutile structure), respectively. The structural distortions of the oxyhydroxides are caused by an interaction of Jahn-Teller distortion of octahedrally coordinated Mn 3؉ (four short and two long Mn-O distances) and hydrogen bonding. In both structures two symmetrically distinct O sites (O1 and O2) are three-coordinated by Mn 3؉ . The choice which O site forms an OH group is governed by the orientation of the Jahn-Teller distortion and space constraints dictated by the octahedral framework topology. The two long Mn-O bonds are formed by both O1 and O2 thus the Jahn-Teller distortion alone does not determine the preference of the OH group. In groutite, the OMn 3 coordination fragment which shows the strongest deviation from planarity toward a trigonal pyramid bonds to H where the O-H vector points perpendicular to the Mn 3 plane. In manganite the coordinations of O1 and O2 are very similar, thus H shows long range disorder as observed by twinning. Both, groutite and manganite have short O-H•••O distances (2.6 A > ) giving rise to peculiar IR absorption features between 3200 and 1800 cm ؊1 . Oriented single-crystal slabs of manganite and diaspore (isostructural to groutite) were studied by polarized FTIR spectroscopy at 82 and 298 K, and all H-bonding related IR-absorptions were assigned. Manganite, -MnOOH, and groutite, -MnOOH, both transform in air above ca. 300°C to -MnO (pyrolusite) which was studied by in situ temperature dependent single-crystal X-ray diffraction. The topotactic relation is preserved during the transformation.