Electrochemical synthesis of a pseudo-two-dimensional polytelluride containing Te^2-₁₂ anions: Structure of [(C₂H₅)₄N]₂Te₁₂

An unusual pseudo-two-dimensional polytelluride built up from Te^2-₁₂ anions was synthesized electrochemically from the cathodic dissolution reaction of an SbTe₁₀ alloy electrode in an ethylenediamine solution of tetraethylammonium iodide, and represents the largest homoatomic polychacogenide anion characterized to date. The compound [(C₂H₅)₄N]₂Te₁₂ crystallizes in the acentric monoclinic space group Pn (No. 7) with lattice constants of a = 7.934(1), b = 17.453(8) and c = 13.514(1) Å, β = 104.671(10)° and V = 1810.4(7) ų, with Z = 2 and R(R_w) = 0.036(0.047). The structure consists of puckered Te^2-₁₂ chains, with internal Te-Te distances of 2.713(2)-2.881(2) Å, loosely bound into infinite two-dimensional sheets via many Te-Te interactions in the range of 3.144(2)-3.504(2) Å. These distances are somewhat shorter than the comparable interchain (2.835(2) Å) and intrachain (3.495(3) Å) Te-Te distances in elemental Te. The complete structure consists of these tellurium layers separated in the crystallographic b direction by layers of tetraethylammonium cations.