Dimers of oxocentred [OCu₄]⁶⁺ tetrahedra in two novel copper selenite chlorides, K[Cu₃O](SeO₃)₂Cl and Na₂[Cu₇O₂] (SeO₃)₄Cl₄, and related minerals and inorganic compounds

Two novel copper selenite chlorides, K[Cu 3 O](SeO 3 ) 2 Cl (I) and Na 2 [Cu 7 O 2 ](SeO 3 ) 4 Cl 4 (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, R 1 = 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, R 1 = 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 (OCu 4 ) 6+ tetrahedra share a common Cu···Cu edge to form the [O 2 Cu 6 ] 8+ dimer, whereas the structure of II is based upon two (OCu 4 ) 6+ tetrahedra linked together by one common Cu atom resulting in the formation of the [O 2 Cu 7 ] 10+ dimer. A comparison with related minerals and inorganic compounds is given.