Syntheses and characterization of some mixed Te/Se polychalcogenide anions [Te_mSe_n]^2-

Several mixed Te/Se polychalcogenide anions [Te_mSe _n]^2- were synthesized at 293 K by reactions between Te_n^2- and Se_n^2- anions in N,N-dimethylformamide (DMF) in the presence of different-size ammonium or phosphonium cations, in some cases in the presence of metal species. The structures of these anions were determined by single-crystal X-ray diffraction methods. The crystal structures of (NEt₄]₂[Te ₃Se₆] (1) and [NEt₄]₂[Te ₃Se₇] (2) consist, respectively, of one-dimensional infinite _∞¹[Te₃Se₆ ^2-] and _∞¹[Te₃Se ₇^2-] anionic chains separated by NEt₄ ⁺ cations. In compound 1, each chain comprises Te₃Se ₅ eight-membered rings bridged by Se atoms. The Te₃Se ₅ ring has an "open book" conformation. The NMR spectrum of a DMF solution of [NEt₄]₂[Te₃Se₆] crystals at 223 K shows ⁷⁷Se resonances at δ = 290, 349, and 771 ppm and a single ¹²⁵Te resonance at δ = 944.7 ppm. In compound 2, each chain comprises Te₃Se₆ five- and six-membered rings bridged by Se atoms. The Te₃Se₆ ring can be regarded as an inorganic analogue of bicyclononane. The anion of [PPh₄]₂[Te₂Se₂] (4) contains a Se-Te-Te-Se chain with the terminal Se atoms trans to one another. The new compounds [PPN]₂[TeSe₁₀] (3), [NMe₄] ₂[TeSe₃]·DMF (5), and [NEt₄] ₂[TeSe₃] (6) contain known anions.