Controlled Synthesis of Pnicogen–Chalcogen Polycations in Ionic Li­quids

Abstract

Three new pnicogen–chalcogen polycations were synthesized under specific conditions in the Lewis-acidic ionic liquids (ILs) [EMIm]X·nAlX₃ and [BMIm]X·nAlX₃ (X = Cl, Br; [EMIm]: 1-ethyl-3-methylimidazolium, [BMIm]: 1-butyl-3-methylimidazolium) and crystallized as their tetrahalogenidoaluminate salts. Single-crystal X-ray diffraction revealed the new polycation [Bi₆Te₄Br₂]⁴⁺ in triclinic [Bi₆Te₄Br₂](AlBr₄)₄ as the reaction product of bismuth, tellurium, and bismuth tribromide. Substitution of the elements with Bi₂Te₃ yielded the heterocubane [Bi₄Te₄]⁴⁺ in tetragonal [Bi₄Te₄](AlBr₄)₄, which crystallizes isotypically to its known chlorine counterpart. The latter is also accessible from ILs. The interactions between cations and anions were evaluated by quantum-chemical calculations. Bi₂S₃, which is insoluble in most media, readily dissolves in the employed IL and forms the new augmented heterocubane [Bi₃S₄AlCl]³⁺, which crystallizes with the complex anion [S(AlCl₃)₃]^2– as triclinic [Bi₃S₄AlCl][S(AlCl₃)₃]AlCl₄. Quantum-chemical calculations support the assignment of elements in this compound. The monoclinic crystal structure of [Sb₁₃Se₁₆](AlCl₄)₆(Al₂Cl₇) contains a new member of the small family of pnicogen–chalcogen spiro-heterocubanes.

Heteropolycations: Three new pnicogen–chalcogen polycations were synthesized in imidazolium-based Lewis-acidic ionic liquids (IL) at moderate temperatures. Bi₂S₃, usually soluble only under harsh conditions, readily dissolves and reacts in the employed IL to give a quaternary polycation. The choice of starting materials and the reaction temperature were identified as important control parameters.

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