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Multidimensional structural variation in the cyanotrichite family of merotypes: camerolaite‐3 b ‐ F
Author(s) -
Mills Stuart J.,
Christy Andrew G.,
Favreau Georges,
Galea-Clolus Valérie
Publication year - 2017
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520617010769
Subject(s) - superstructure , crystallography , octahedron , bar (unit) , group (periodic table) , rod , tetrahedron , alternation (linguistics) , order (exchange) , unit (ring theory) , crystal structure , materials science , chemistry , combinatorics , geometry , physics , mathematics , thermodynamics , medicine , linguistics , alternative medicine , philosophy , organic chemistry , finance , pathology , meteorology , economics , mathematics education
A new superstructure of the mineral camerolaite, Cu 6 Al 3 (OH) 18 (H 2 O) 2 [Sb(OH) 6 ](SO 4 ), has been refined in space group P with unit‐cell parameters a P = 7.7660 (16), b P = 8.759 (4), c P = 11.306 (2) Å, α P = 108.67 (4), β P = 83.41 (3), γ P = 126.64 (2)°, V = 581.6 (3) Å 3 and Z = 1, with R 1 = 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 [SO 4 ] and [Sb(OH) 6 ] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO 4 ] groups of adjacent rods along a and c directions. This arrangement suggests an alternative nearly orthogonal choice of unit cell in F with parameters a F = 12.473 (26), b F = 8.759 (4), c F = 21.476 (7) Å, α F = 85.94 (4), β F = 95.91 (5), γ F = 92.34 (9)°, which is recommended for comparing this structural variety of camerolaite with other members of the group.