The crystal structure of fedotovite, K2Cu3O(SO4)3 has been determined, space group C2/c, a 19.037(6), b 9.479(2), c 14.231(5) Å, β 111.04(3)°, Z = 8, Dx = 3.09 g/cm3. 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 Cu1 and Cu2 atoms are distorted and flattened orthorhombic pyramids with Cu-O distances varying from 1.912 to 2.333 Å, the sixth neighbour of the both atoms is the copper atom lying at 2.975 and 2.981 Å for Cu2 and Cu1 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 Å, a fifth at 2.558 Å, and further sixth and seventh neighbours (oxygen and copper atoms) at 2.809 and 2.806 Å, respectively.

Two novel copper selenite chlorides, K[Cu3O](SeO3)2Cl (I) and Na2[Cu7O2](SeO3)4Cl4 (II), have been synthesized by the CVT method. Their crystal structures have been solved by direct methods and refined by least-squares techniques. I is triclinic, space group P1̄, a = 7.6821(5), b = 8.1179(5), c = 8.7836(6) Å, α = 113.193(3), β = 108.735(4), γ = 98.245(4)°, V = 453.32(5) Å3, R1 = 0.0481 for 1210 unique reflections with F≥4σ(F); II is triclinic, space group P1̄,a = 7.4362(6), b = 8.3361(7), c = 9.1343(11) Å,α = 110.277(6), β = 106.212(6), γ = 105.158(4)°, V = 467.94(8) Å3, R1 = 0.0265 for 2498 unique reflections with F≥4σ(F). The structures of I and II can be described in terms of dimers of copper oxocentred tetrahedra. In I, two (OCu4)6+ tetrahedra share a common Cu···Cu edge to form the [O2Cu6]8+ dimer, whereas the structure of II is based upon two (OCu4)6+ tetrahedra linked together by one common Cu atom resulting in the formation of the [O2Cu7]10+ dimer. A comparison with related minerals and inorganic compounds is given.