Contribution to the crystal chemistry of tetrametaphosphates (I)

Crystal structures of K₄P₄O₁₂ · 2H₂O and of two polymorphs of Na₂K₂P₄O₁₂ · 2H₂O are reported. K₄P₄O₁₂ · 2H₂O is triclinic P1 with a = 8.153(4), b = 8.222(4), c = 11.154(8) Å, α = 97.33(5), β = 95.46(5), γ = 88.92(5)°, and Z = 2. R = 0.021 for 2898 reflections. Na₂K₂P₄O₁₂ · 2H₂O has two crystalline forms: a triclinic one ($\text{P}\text{1}$) with a = 11.366(8), b = 7.908(5), c = 7.929(5) Å, α = 90.07(5), β = 106.85(5), γ = 95.66(5)°, and Z = 2, and a tetragonal one (P4₁) with a = 7.928(5), c = 21.66(2), and Z = 4. The crystal structures of the first and second crystalline forms have been solved with final R values of 0.022 for 2505 reflections and 0.036 for 1347 reflections, respectively. Crystal data and chemical preparations are given for Na₂(NH₄)₂P₄O₁₂ · 2H₂O and Na₂Rb₂P₄O₁₂ · 2H₂O, both isotypic with the triclinic form of Na₂K₂P₄O₁₂ · 2H₂O. Unit-cell dimensions are, respectively, a = 11.547(8), b = 8.012(5), c = 8.044(5) Å, α = 89.76(5), β = 106.22(5), and γ = 94.78(5)°, for the ammonium salt, and a = 11.577(8), b = 8.006(5), c = 8.032(5) Å, α = 89.79(5), β = 106.58(5), and γ = 95.19(5)° for the rubidium salt. In addition the crystal structures of the two crystalline forms of Na₄P₄O₁₂ · 4H₂O were reexamined in order to localize the hydrogen atoms and refine their positions.