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A new superstructure of the mineral camerolaite, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4), has been refined in space group P
with unit-cell parameters aP = 7.7660 (16), bP = 8.759 (4), cP = 11.306 (2) Å, αP = 108.67 (4), βP = 83.41 (3), γP = 126.64 (2)°, V = 581.6 (3) Å3 and Z = 1, with R1 = 0.0951 (all data). This is the first refined example of a cyanotrichite-group mineral in which long-range order of interlayer anions produces a superstructure along b, although diffuse scattering has previously been reported that corresponds to short-range order. Though the structure shares with other members of the cyanotrichite group a structural unit in which ribbons of edge-sharing Cu and Al octahedra form layers || (001), the superstructure arises from regular alternation of [SO4] and [Sb(OH)6] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO4] groups of adjacent rods along a and c directions. This arrangement suggests an alternative nearly orthogonal choice of unit cell in F with parameters aF = 12.473 (26), bF = 8.759 (4), cF = 21.476 (7) Å, αF = 85.94 (4), βF = 95.91 (5), γF = 92.34 (9)°, which is recommended for comparing this structural variety of camerolaite with other members of the group.
with unit-cell parameters aP = 7.7660 (16), bP = 8.759 (4), cP = 11.306 (2) Å, αP = 108.67 (4), βP = 83.41 (3), γP = 126.64 (2)°, V = 581.6 (3) Å3 and Z = 1, with R1 = 0.0951 (all data). This is the first refined example of a cyanotrichite-group mineral in which long-range order of interlayer anions produces a superstructure along b, although diffuse scattering has previously been reported that corresponds to short-range order. Though the structure shares with other members of the cyanotrichite group a structural unit in which ribbons of edge-sharing Cu and Al octahedra form layers || (001), the superstructure arises from regular alternation of [SO4] and [Sb(OH)6] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO4] groups of adjacent rods along a and c directions. This arrangement suggests an alternative nearly orthogonal choice of unit cell in F with parameters aF = 12.473 (26), bF = 8.759 (4), cF = 21.476 (7) Å, αF = 85.94 (4), βF = 95.91 (5), γF = 92.34 (9)°, which is recommended for comparing this structural variety of camerolaite with other members of the group.
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