The crystal structure of fedotovite, KzCu30(SO4)3 has been determined, space group C2/c, a 19.037(6), b 9.479(2), c 14.231(5) ~, [3 111.04(3) ~ Z = 8, Dx = 3.09 g/cm 3. The main units of the fedotovite structure are formed around two additional oxygen atoms and consist of edge-sharing [OCu4] tetrahedra and four [SO4] tetrahedra attached to them. The units are further connected by two [SO4] tetrahedra, building distinct layers parallel to the yz plane. These layers are interconnected by potassium atoms. In the fedotovite structure, the three kinds of copper atoms are fivefold (4 + 1) coordinated to oxygen atoms with a strong Jahn-Teller effect. The coordination polyhedra of Cul and Cu2 atoms are distorted and flattened orthorhombic pyramids with Cu-O distances varying from 1.912 to 2.333/~,. the sixth neighbour of the both atoms is the copper atom lying at 2.975 and 2.981 ~ for Cu2 and Cul respectively. The coordination environment of the Cu3 atom is a distorted elongated orthorhombic pyramid with four Cu-O distances from 1.943 to 1.961 A, a fifth at 2.558 A, and further sixth and seventh neighbours (oxygen and copper atoms) at 2.809 and 2.806 A, respectively.

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The crystal structure of averievite, Cu5O2(VO4)2·nMX has been determined. Trigonal system, space group P3, a = 6.375(1), c = 8.399(1) Å, V = 295.6(1) Å3, Z = 1, Dx = 4.01(1) g/cm3. The atomic arrangement is characterized by infinite nets parallel to (001) composed of [OCu4]6+ tetrahedra linked via corners in hexagonal rings. The bases of neigbouring tetrahedra are in one plane and their non-shared corners are turned to the opposite sides. The [VO4]3− tetrahedra are attached to the bases of [OCu4] tetrahedra. There are large (R >3.2 Å) channels in the structure where large molecular particles can enter. The comparison of the averievite structure with related compounds (in particular, copper oxovanadates) is given from the point of view of [OT4] polyion crystal chemistry.

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