Crystal and molecular structure of guanidinium hexatungsto‐bis(p‐aminophenylarsonate) tetrahydrate,[C(NH2)3]4[p‐NH3C6H4As)2W6O25]·4H2O

The crystal structure of a new type arylarsonic polytungstate [C(NH2)3]4[p-NH3C6H4As)2W6O25]·4H2O was determined by single-crystal X-ray diffraction analysis. It belongs to triclinic, space group , with cell dimensions a = 12.863(3), b = 18.912(3), c = 21.383(4) A α = 91.14(2)°, β = 93.65(3)°, γ = 92.25(3)°, V = 5185.9 A3, Z = 4, Dc = 2.753 g/cm3. The intensity data were collected on an Enraf-Nonius CAD4 diffractometer with Mo Kα radiation. The positions of all tungsten and arsenic atoms were determined by direct method. The other non-hydrogen atoms were revealed by difference Fourier synthesis. The structure was refined by fullmatrix least-squares procedure to a final R value of 0.070. The crystal structure contains two similar but nonidentical molecules. Two similar anions consist of a ring of six WO6 octahedra, which are connected with one face-sharing, two corner-sharings and three edge-sharings, and two p-aminophenylarsonic tetrahedra capped above and below the ring. In each WO6 ring, four tungsten atoms, which are joined with edge-sharing oxygen atoms, are almost coplanar, while the two others, which are joined with face-sharing oxygen atoms, protrude out of the ring towards the same side. The two arsenic atoms in each anion are not equivalent in their bonding manner. In each anion, all non-hydrogen atoms of each organic group are in the same plane. Each molecule contains one anion, four C(NH2)3+ cations and four water molecules. There are many hydrogen bonds between cations and anions throughout the whole crystal. The amino groups can accept protons, so that the charge of the resulting anion decreases and [(RAs)2W6O25]4- type complexes are formed.