Five-coordinate Cd in the crystal structure of triploidite-type Cd2(AsO4)(OH)

Tamara Đorđević, Uwe Kolitsch

Veröffentlichungen: Beitrag in FachzeitschriftArtikelPeer Reviewed


This paper reports on hydrothermal synthesis and crystal structure refinement of dicadmium arsenate hydroxide, Cd2(AsO4)(OH), obtained at 220 °C and autogenous pressure. Its crystal structure is monoclinic, space group P21/a, with a = 13.097(3), b = 14.089(3), c = 10.566(2) Å, ß = 108.38(3)°, V = 1850.2(6) Å3 (Z = 16). It is isotypic with the members of the triploidite group of minerals and synthetic compounds, and thus shows a close topological relationship with the triplite group. The complex framework contains edge- and corner-sharing CdO4(OH) and CdO4(OH)2 polyhedra, linked via corner-sharing to AsO4 tetrahedra (average As-O distances range between 1.682 and 1.688 Å). Four five-coordinated Cd sites are at the centers of distorted trigonal bipyramids (average Cd-O distances are between 2.225 and 2.251 Å), whereas the remaining four Cd sites have a distorted octahedral coordination environment (average Cd-O distances are between 2.297 and 2.320 Å). The positions of all the hydrogen atoms were located in a difference-Fourier map and refined with an isotropic displacement parameter. The hydrogen-bonds are weak to very weak. The unusual five-coordination of Cd is briefly discussed in relation to comparable minerals and compounds. Among triploidite-type compounds, Cd2(AsO4)(OH) is the member with the largest unit cell reported so far, and the second known arsenate member.
Seiten (von - bis)243-251
FachzeitschriftMineralogy and Petrology
PublikationsstatusVeröffentlicht - 2013

ÖFOS 2012

  • 105113 Kristallographie


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