Refinement of the crystal structure of averievite Cu5O2(VO4)·nМСlx(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)nMClx (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.
