TY - JOUR
T1 - Acentric structure (P3) of bechererite, Zn7Cu(OH)13[SiO(OH)3SO4]
AU - Hoffmann, Christina
AU - Armbruster, Thomas
AU - Giester, Gerald
PY - 1997
Y1 - 1997
N2 - The crystal structure of bechererite from the Tonopah-Belmont mine, Arizona, was reinvestigated using a single-crystal X-ray diffractometer (MoKα radiation) equipped with a CCD area detector. The structure was refined in space group P3 (a = 8.319(2), c = 7.377(1) Å) with 1247 unique reflections up to (sinθ)/λ = 0.65 leading to R1 = 2.7%, wR2 = 6.4%. In agreement with the previously reported centric structure (P3), bechererite is composed of (001) brucite-like sheets formed by edge-sharing (Zn,Cu)O6 octahedra and 1/7 ordered octahedral vacancies. The layers are connected parallel to c by ditetrahedral (Zn,Cu)2(OH)7 units. Due to the attractive force of a weak hydrogen bond, the bridging O atom of the ditetrahedral unit is displaced from the threefold axis. A characteristic feature of the structure is isolated tetrahedra, which connect only with one apex to the octahedral sheet. The acentric structure (P3) reveals ordering between SiO(OH)3 and SO4 tetrahedra yielding characteristic distortions of the neighboring (Zn,Cu)O6 octahedra caused by bond-valence requirements of the shared O atoms. The [SiO(OH)3]1- tetrahedron is only 70(1)% occupied and is partly substituted by tetrahedral [O4H7]1- clusters. The existence of H2O molecules in the [O4H7]1- cluster is supported by FTIR spectroscopy.
AB - The crystal structure of bechererite from the Tonopah-Belmont mine, Arizona, was reinvestigated using a single-crystal X-ray diffractometer (MoKα radiation) equipped with a CCD area detector. The structure was refined in space group P3 (a = 8.319(2), c = 7.377(1) Å) with 1247 unique reflections up to (sinθ)/λ = 0.65 leading to R1 = 2.7%, wR2 = 6.4%. In agreement with the previously reported centric structure (P3), bechererite is composed of (001) brucite-like sheets formed by edge-sharing (Zn,Cu)O6 octahedra and 1/7 ordered octahedral vacancies. The layers are connected parallel to c by ditetrahedral (Zn,Cu)2(OH)7 units. Due to the attractive force of a weak hydrogen bond, the bridging O atom of the ditetrahedral unit is displaced from the threefold axis. A characteristic feature of the structure is isolated tetrahedra, which connect only with one apex to the octahedral sheet. The acentric structure (P3) reveals ordering between SiO(OH)3 and SO4 tetrahedra yielding characteristic distortions of the neighboring (Zn,Cu)O6 octahedra caused by bond-valence requirements of the shared O atoms. The [SiO(OH)3]1- tetrahedron is only 70(1)% occupied and is partly substituted by tetrahedral [O4H7]1- clusters. The existence of H2O molecules in the [O4H7]1- cluster is supported by FTIR spectroscopy.
UR - http://www.scopus.com/inward/record.url?scp=0001113501&partnerID=8YFLogxK
U2 - 10.2138/am-1997-9-1018
DO - 10.2138/am-1997-9-1018
M3 - Article
AN - SCOPUS:0001113501
SN - 0003-004X
VL - 82
SP - 1014
EP - 1018
JO - American Mineralogist
JF - American Mineralogist
IS - 9-10
ER -