Two modifications of (TeO)(HAsO₄) and its dehydration product (Te₃O₃)(AsO₄)₂. Three more examples of tellurium(IV) with a fivefold oxygen coordination

Two modifications of (TeO)(HAsO₄) were obtained by reacting tellurium dioxide with arsenic acid under boiling conditions (modification I, acid concentration 80 wt-%) or under hydrothermal conditions (modification II, acid concentration 50 wt-%). The crystal structures of the two modifications were determined from single-crystal X-ray data modification I: P2₁/c, Z = 4, a = 7.4076(10), b = 5.9596(7), c = 9.5523(11) Aa, β = 102.589(8) , 2893 structure factors, 68 parameters, R[F² > 2σ(F²)] = 0.0247, wR₂(F² all) = 0.0530; modification II: P2₁/c, Z = 4, a = 6.2962(4), b = 4.7041(3), c = 13.9446(8) Aa, β = 94.528(3) , 2549 structure factors, 69 parameters, R[F² > 2σ(F²)] = 0.0207, wR₂(F² all) = 0.0462. Dehydration of (TeO)(HAsO₄)-II at temperatures above 260 C results in the formation of polycrystalline (Te₃O₃)(AsO₄)₂. Single crystals of the anhydrous product were grown either by heating stoichiometric amounts of the binary oxides TeO₂ and As₂O₅ in closed silica glass ampoules or with higher concentrated arsenic acid (80 wt-%) under hydrothermal conditions at 220 C. The common features in the crystal structures of (Te₃O₃)(AsO₄)₂ [P anti 1], Z = 4, a = 6.5548(4), b = 7.6281(6), c = 15.0464(15) Aa, α = 140.212(6), β = 102.418(9) , γ = 77.346(5) , 5718 structure factors, 146 parameters, R[F² > 2σ(F²)] = 0.0351, wR₂(F² all) = 0. 1093 and in that of the two modifications of acidic (TeO)(HAsO₄) are [TeO₅] square-pyramids and [AsO₄] tetrahedra. In anhydrous (Te₃O₃)(AsO₄)₂ and in (TeO)(HAsO₄)-II, a layered arrangement of the building units is found, whereas in the (TeO)(HAsO₄)-I structure strands are formed. Different hydrogen bonding interactions are present in the two modifications of (TeO)(HAsO₄). (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)