[Te8]2[Ta4O4Cl16]: A Two‐dimensional Tellurium Polycation obtained via Ionic Liquid‐Based Synthesis

By reaction of elemental tellurium, tellurium(IV) chloride, tantalum(V) chloride and tantalum(V) oxychloride in the ionic liquid BMIM]Cl (BMIM]Cl:1‐Butyl‐3‐methylimidazolium chloride),Te₈]₂Ta₄O₄Cl₁₆] is obtained in the form of lucent black crystals. The title compound consists of infinite Te–Te–(Te₆)]_n²⁺ chains (Te–Te: 264.9(1)–284.3(1) pm) and isolated Ta₄O₄Cl₁₆]^4– anions. The Te–Te–(Te₆)]_n²⁺ chains are interconnected to form a two‐dimensional tellurium network (Te–Te: 335.9 pm). Due to this interaction the Te–Te–(Te₆)]_n²⁺ chains in Te₈]₂Ta₄O₄Cl₁₆] show an arrangement that differs significantly from known polycationic Te₈]_n²⁺ chains. The two‐dimensional tellurium network is finally separated by tetrameric, corner‐sharing oxidochloridotantalate anions (TaO_2/2Cl_4/1)₄]^4– that are firstly observed. The composition of Te₈]₂Ta₄O₄Cl₁₆] is confirmed by EDX analysis; its optical band gap is estimated to 1.1–1.2 eV via UV/Vis spectroscopy.