New copper selenites.: Part A:: K2Cu2(SeO3)3 and K2Cu3(SeO3)4

The new compounds K2Cu2(SeO3)(3) and K2Cu3(SeO3)(4) were synthesized in the course of low-hydrothermal experiments on natrochalcite-type selenate representatives. The crystal structures were determined by direct methods from single-crystal X-ray diffraction data. K2Cu2(SeO3)(3): space group Cmcm, Z = 4, a = 5.312(1) Angstrom, b = 9.858(3) Angstrom, c = 17.595(5) Angstrom, V = 921.4(4) Angstrom(3), R1 = 0.023. K2Cu3(SeO3)(4): space group P (1) over bar, Z = 1, a = 5.443(1) Angstrom, b = 7.158(2) Angstrom, c = 8.369(3) Angstrom, a = 95.26(2)degrees, beta = 108.58(2)degrees, gamma = 92.17(2)degrees, V = 307.0(2) Angstrom(3); R1 = 0.035. Both compounds contain sheets built from edge-or cornersharing CuOn polyhedra (n = 5,6) and trigonal pyramidal selenite groups. These units are linked via the potassium atoms. In K2Cu2(SeO3)(3) one of the two selenite groups is strongly disordered.