Two Modifications of (TeO)(HAsO 4 ) and its Dehydration Product (Te 3 O 3 )(AsO 4 ) 2 – Three more Examples of Tellurium(IV) with a Fivefold Oxygen Coordination

Two modifications of (TeO)(HAsO 4 ) 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: P 2 1 / c , Z = 4, a = 7.4076(10), b = 5.9596(7), c = 9.5523(11) Å, β = 102.589(8)°, 2893 structure factors, 68 parameters, R [ F 2 > 2 σ ( F 2 )] = 0.0247, wR 2 ( F 2 all) = 0.0530; modification II: P 2 1 / c , Z = 4, a = 6.2962(4), b = 4.7041(3), c = 13.9446(8) Å, β = 94.528(3)°, 2549 structure factors, 69 parameters, R [ F 2 > 2 σ ( F 2 )] = 0.0207, wR 2 ( F 2 all) = 0.0462)]. Dehydration of (TeO)(HAsO 4 )‐II at temperatures above 260 °C results in the formation of polycrystalline (Te 3 O 3 )(AsO 4 ) 2 . Single crystals of the anhydrous product were grown either by heating stoichiometric amounts of the binary oxides TeO 2 and As 2 O 5 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 (Te 3 O 3 )(AsO 4 ) 2 [ P $\bar{1}$ , Z = 4, a = 6.5548(4), b = 7.6281(6), c = 15.0464(15) Å, α = 140.212(6), β = 102.418(9)°, γ = 77.346(5)°, 5718 structure factors, 146 parameters, R [ F 2 > 2 σ ( F 2 )] = 0.0351, wR 2 ( F 2 all) = 0. 1093] and in that of the two modifications of acidic (TeO)(HAsO 4 ) are [TeO 5 ] square‐pyramids and [AsO 4 ] tetrahedra. In anhydrous (Te 3 O 3 )(AsO 4 ) 2 and in (TeO)(HAsO 4 )‐II, a layered arrangement of the building units is found, whereas in the (TeO)(HAsO 4 )‐I structure strands are formed. Different hydrogen bonding interactions are present in the two modifications of (TeO)(HAsO 4 ).