Refinement of the crystal structure of averievite Cu₅O₂(VO₄)·nМСl_x(М=Сu,Cs,Rb,К)

Krivovichev S. V., Filatov S. K.. Vergasova L. P.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 4. P. 101-109

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Language: Russian

Abstract

Crystal structure of averievite Cu₅O₂(VO₄)_nMCl_x (M = Cu, Cs, Rb, K) has been refined using the holotype specimen from the Tolbachik volcano in the space group P3m1 [a = 6.3778(2), c = 8.3966(3) Å] to R = 0.041 for 489 independent reflections with F > 4 σ (F). The structure contains two Cu sites, of which Cu1 has a square-planar coordination, whereas the Cu2 site has a trigonal bipyramidal coordination. One symmetrically independent V⁵⁺ cation forms vanadate tetrahedra with the average bond length <V—O> = 1.714 Å. Among three symmetrically independent O sites, the Oq atom is not bonded with V⁵⁺ cations, and is coordinated by four Cu atoms, forming the oxocentered (OCu₄)⁶⁺ tetrahedron. These tetrahedra, sharing their vertices, form [O₂Cu₅]⁶⁺ sheets of six-member rings, in which two joint tetrahedra are oriented into opposite directions relatively to the sheet plane parallel to (100). Triangular faces of oxocentered tetrahedra are linked to the (VO₄)^3– tetrahedra according to the ‘face-to-face’ principle, which results in formation of electroneutral porous framework {[O₂Cu₅](VO₄)₂}⁰ with wide channels elongated parallel to the c axis and having crystallographic free diameter about 3.7 Å. The channels accommodate two cations (M1, M2) and one anion (C1) sites with the 1 : 1 cation : anion ratio.

Key words: averievite, crystal structure, Tolbachik, oxocentered tetrahedra, copper.