Acta Cryst. (2012). E68, i3-i4 [ doi:10.1107/S1600536811052020 ]
Abstract: The structure of the title compound, (Ag0.79Co0.11)Co(H2O)2[BP2O8]·0.67H2O is isotypic to that of its recently published counterparts AgMg(H2O)2[BP2O8]·H2O and (Ag0.57Ni0.22)Ni(H2O)2[BP2O8]·0.67H2O. It consists of infinite borophosphate helical ribbons [BP2O8]3-, built up from alternate BO4 and PO4 tetrahedra arranged around the 65 screw axes. The vertex-sharing BO4 and PO4 tetrahedra form a spiral ribbon of four-membred rings in which BO4 and PO4 groups alternate. The ribbons are connected through slightly distorted CoO4(H2O)2 octahedra whose four O atoms belong to the phosphate groups. The resulting three-dimensional framework is characterized by hexagonal channels running along  in which the remaining water molecules are located. The main difference between the Mg-containing and the title structure lies in the filling ratio of Wyckoff positions 6a and 6b in the tunnels. The refinement of the occupancy rate of the site 6a shows that it is occupied by water at 67%, while the refinement of that of the site 6b shows that this site is partially occupied by 78.4% Ag and 10.8% Co, for a total of 82.2%. The structure is stabilized by O-HO hydrogen bonds between water molecules and O atoms that are part of the helices.
Online 7 December 2011
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