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

Abstract

The crystal structures of the four synthetic double salt compounds K₂Mn(SO₄)₂·2H₂O (space group P1̅, no. 2, Z = 2, a = 6.574(1), b = 7.332(1), c = 10.700(1) Å, α = 72.89(1), β = 73.91(1), γ = 69.77(1)°, V = 453.6(1) ų) and K₂Cd(SeO₄)₂·2H₂O(space group P1̅, no. 2, Z = 2, a = 6.625(1), b = 7.542(1), c = 11.349(1) Å, α = 72.17(1), β = 74.55(1), γ = 70.13(1)°, V = 499.3(1) ų) as well as (NH₄)₂Cu(SeO₄)₂·2H₂O (space group P1̅, no. 2, Z = 1, a = 5.784(1) Å, b = 7.107(1) Å, c = 7.371(1) Å, α = 104.21(2)°, β = 93.04(2)°, γ = 112.27(2)°, V = 268.19(7) ų), and KFeH(SO₄)₂·2H₂O(space group P1̅, no. 2, Z = 1, a = 4.626(1), b = 5.820(1), c = 8.265(1) Å, α = 103.86(1), β = 99.77(1), γ = 95.66(1)°, V = 210.64(2) ų) 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 kröhnkite [Na₂Cu(SO₄)₂·2H₂O]-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)₂·2H₂O is a disordered H atom involved in a short hydrogen bond, which shows no ordering down to 110 K.