Electrochemical Synthesis and Structural Characterization of the One-Dimensional Chain Compound (Et₄N)₂[As₂Te₅] and the Tellurido Arsenate (Me₄N)₄[As₄Te₆]·2en

The new arsenic telluride (Et₄N)₂[As₂Te₅] (1) has been prepared by electrolytically dissolving As₂Te₃ cathodes into an ethylenediamine solution of Et₄NI. Telluride 1 crystallizes in the triclinic space group P1 with lattice constants a = 9.296(2), b = 11.341(4), c = 7.829(2) Å, α = 104.31(2)°, β = 98.60(2)°, γ = 112.54(2)°, V = 710.6(4) ų, Z = 1, and R(R_w) = 0.064(0.058). The structure consists of infinite one-dimensional As₂Te₅²⁻ chains running parallel to the c axis which are surrounded by Et₄N⁺ cations. The structure of the unique As₂Te₅^2- chain is built up from alternating As₂⁴⁺ dimers (As-As = 2.451(8) Å) and square planar Te₅^6- fragments with As-Te contacts of 2.587(5) and 2.598(4) Å. The Te₅^6- moieties contain a central square-planar tellurium atom bonded to the neighboring four Te atoms at 3.058(4) Å (2X) and 3.009(3) Å (2X). Changing the supporting electrolyte to Me₄NI allows (Me₄N)₄[As₄Te₆]·2en (2) to be isolated. Telluride 2 crystallizes in the monoclinic space group P2₁/n with a = 11.905(3), b = 10.347(4), c = 19.017(5) Å, β = 100.92(2)°, V = 2300(1) ų, Z = 2 and R (R_w) = 0.062 (0.063). Like 1, telluride 2 contains As₂⁴⁺ dimers bonded to four tellurium atoms but forms an As₄Te₂ six-membered ring with an exocyclic terminal Te atom on each arsenic.