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  • Water in the alluaudite type-compounds: synthesis, crystal structure and magnetic properties of ▫${\rm Co_3(AsO_4)_{0.5+x}(HAsO_4)_{2-x}(H_2AsO_4)_{0.5+x}[(H,\Box)_{0.5}(H_2O, H_3O)_{0.5}]^{2x+}}$▫ [Elektronski vir]
    Đorđević, Tamara, 1976- ...
    In this study, a new cobalt arsenate belonging to the alluaudite supergroup compounds with the general formula of ▫${\rm Co_3(AsO_4)_{0.5+x}(HAsO_4)_{2-x}(H_2AsO_4)_{0.5+x}[(H,\Box)_{0.5}(H_2O, ... H_3O)_{0.5}]^{2x+}}$▫ (denoted as ▫${\rm CoAsAllu}$▫) was synthesized under hydrothermal conditions. Its crystal structure was determined by a room-temperature single-crystal X-ray diffraction analysis: space group ▫${\rm C2/c, \; a = 11.6978(8),\; b = 12.5713(7), \; c = 6.7705(5) \AA, \beta = 113.255(5)^\circ, \; V = 914.76(11) \AA^3,\; Z = 2}$▫ for ▫${\rm As_6H_8Co_6O_{25}}$▫. It represents a new member of alluaudite-like protonated arsenates and the first alluaudite-like phase showing both protonation of the tetrahedral site and presence of the ▫${\rm H_2O}$▫ molecules in the channels. In the asymmetric unit of ▫${\rm CoAsAllu}$▫, one of the two Co, one of the two As and one of the seven O atoms lie at ▫$4e$▫ special positions (site symmetry 2). The crystal structure consists of the infinite edge-shared ▫${\rm CoO_6}$▫ octahedra chains, running parallel to the ▫$[10\overline{1}]$▫ direction. The curved chains are interconnected by ▫${\rm [(As1O_4)_{0.5}(H_2As1O_4)_{0.5}]^{2-}}$▫ and ▫${\rm [HAs_2O_4]^{2-}}$▫ tetrahedra forming a heteropolyhedral 3D open framework with two types of parallel channels. Both channels run along the ▫$c$▫-axis and are located at the positions (1/2, 0, z) and (0, 0, z), respectively. The H2 and H4 hydrogen atoms of O2H2 and O4H4 hydroxyl groups are situated in channel 1, while the uncoordinated water molecule ▫${\rm H_2O7}$▫ at half-occupied 4e special positions and hydrogen atoms of O6H6 hydroxyl group were found in channel 2. The results of the magnetic investigations confirm the quasi one-dimensional structure of divalent cobalt ions. They are antiferromagnetically coupled with the intrachain interaction parameter of ▫$J \approx -8$▫ cm▫$^{-1}$▫ and interchain parameter of ▫$J’ \approx -2$▫ cm▫$^{-1}$▫ that become effective below the Néel temperature of 3.4 K.
    Vir: Minerals [Elektronski vir]. - ISSN 2075-163X (Vol. 11, iss. 12, Dec. 2021, art. 1372 (14 str.))
    Vrsta gradiva - e-članek ; neleposlovje za odrasle
    Leto - 2021
    Jezik - angleški
    COBISS.SI-ID - 90022403

    Povezava(-e):

    https://www.mdpi.com/2075-163X/11/12/1372
    DOI

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