Crystal structures of the double salt dihydrates K2Cd(SeO4)2 • 2 H2O, K2Mn(SO4)2 • 2H2O, (NH4)2Cu(SeO4)2 • 2 H2O and KFeH(SO4)2 • 2H2O

The crystal structures of the four synthetic double salt compounds K2Mn(SO4)(2) - 2 H2O (space group P (1) over bar, no. 2, Z = 2, a = 6.574(1), b = 7.332(1), c = 10.700(1) Angstrom, alpha = 72.89(1), beta = 73.91(1), gamma = 69.77(1)degrees, V = 453.6(1) Angstrom(3)) and K2Cd(SeO4)(2) . 2 H2O (space group P (1) over bar, no. 2, Z = 2, a = 6.625(1), b = 7.542(1), c = 11.349(1) Angstrom, alpha = 72.17(1), beta = 74.55(1), gamma = 70.13(1)degrees, V = 499.3(1) Angstrom(3)) as well as (NH4)(2)Cu(SeO4)(2) . 2 H2O (space group P (1) over bar, no. 2, Z = 1, a = 5.7840) Angstrom, b = 7.107(1) Angstrom, c = 7.371(1) Angstrom, alpha = 104.21(2)degrees, beta = 93.04(2)degrees, gamma = 112.27(2)degrees, V = 268.19(7)Angstrom(3)), and KFeH(SO4)(2) . 2 H2O (space group P (1) over bar, no. 2, Z = 1 a = 4.626(1), b = 5.820(1), c = 8.265(1) Angstrom, alpha = 103.86(1), beta = 99.77(1), gamma = 95.66(1)degrees, V = 210.64(2) Angstrom(3)) have been determined from single-crystal X-ray diffraction data collected with a CCD area detector at 293 K, and were refined to R(F) = 0.0231, 0.0251, 0.0230 and 0.0194, respectively. The first two compounds are isostructural. The atomic arrangements are described, with a focus on the hydrogen bonding. All compounds contain krohnkite [Na2Cu(SO4)(2) . 2H(2)O]-type tetrahedral-octahedral chains but show different topological arrangements of these chains. A classification is proposed in an accompanying paper. A particular feature of KFeH(SO4)(2) . 2 H2O is a disordered H atom involved in a short hydrogen bond, which shows no ordering down to 110 K.