(Cr3AsO13)3−: Un nouveau type d'anion condensé. Préparation chimique et données cristallographiques sur (NH4)2HCr3AsO13

(NH₄)₂HCr₃AsO₁₃ is monoclinic ($\text{P2}{}_1\text{c}$) with a tetramolecular unit cell: a = 13.99(1), b = 9.47(1), c = 9.55(1) Å, and β = 93.10(1)°. We describe the chemical preparation and give crystal data for this compound.     

(NH4)4P4O12 · 2Te(OH)6 · 2H2O,the first example of a tetrametaphosphate-tellurate

Ammonium tetrametaphosphate-tellurate dihydrate, (NH₄)₄P₄O₁₂ · 2Te(OH)₆ · 2H₂O, is triclinic with the following unit cell dimensions: a = 11.845(6), b = 8.554(5), c = 7.433(5) Å, α = 66.28(5), β = 95.91(5), γ = 76.00(5)° space group: $\text{P}\text{1}$ and Z = 1. The crystal structure has been determined with a final R value of 0.021. As in the previously described phosphate-tellurates, monophosphate-tellurate and trimetaphosphate-tellurates, the phosphoric anion (here the P₄O₁₂ ring) is independent of the octahedral Te(OH)₆ group. A complete pattern of the hydrogen bonds is given.     

Crystal structure of cerium(III) diammonium polyphosphate (NH4)2Ce(PO3)5

Cerium(III) diammonium polyphosphate, (NH₄)₂Ce(PO₃)₅, is triclinic P1 with the following unit cell dimensions: a = 7.241(5) Å, b = 13.314(8) Å, c = 7.241(5)Å, α = 90.35(5)°, β′ = 107.50(5)°, γ = 90.28(5)°, and Z = 2, V = 665.7 ų, D_x = 2.85 g/cm³. The crystal structure of this new type of polyphosphate has been solved and refined from 4130 independent reflections to a final R value 0.029. The most interesting feature of this salt is the existence of two infinite crystallographically nonequivalent (PO₃)^?_∞ chains, one running parallel to the a axis, the other along the c axis, both with a period of five tetrahedra. This compound seems to be the first example of a long chain polyphosphate with crystallographic independent chains.     

Crystal Structure of a Tetrapoly-Dipolyphosphate: CaNb2O(P4O13)(P2O7)

Chemical preparation and crystal structure of CaNb₂O(P₄O₁₃)(P₂O₇) are described. The monoclinic unit cell has the following dimensions: a = 13.264(9), b = 10.577(8), c = 12.393(9) Å, β = 96.09(1)°. Space group is C2/m with Z = 4. The crystal structure has been solved by using 1204 unique reflexions with a final R value 0.049. The main outstanding feature of this compound rests on the coexistence in its atomic arrangement of two kinds of phosphate anions with different degrees of condensation: a tetrameric linear one: (P₄O₁₃)^6? and dimeric linear one: (P₂O₇)^4?. The atomic arrangement can be schematically described as a stacking of alternating rows of P₄O₁₃ and P₂O₇ groups, parallel to the ā axis. The P₄O₁₃ groups have a twofold symmetry while the P₂O₇ groups have a non usual mirror symmetry. One of the oxygen atoms does not belong to the phosphoric groups.     

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.