The chain-like polynuclear coordination compounds (ZnBr2)n(18-crown-6)2 (n = 4, 6, 8, 10) and [Zn5Br9][N(Tf2)]

Abstract

The chain-like polynuclear coordination compounds (ZnBr₂)_n(18-crown-6)₂ (n = 4, 6, 8, 10) and [Zn₅Br₉][N(Tf)₂] are obtained by reacting ZnBr₂, SnBr₄ and 18-crown-6 in the ionic liquid [(n-Bu)₃MeN][N(Tf)₂] (N(Tf)₂: bis(trifluoromethylsulfonyl)imide). Structurally, chain-like anionic building units with corner- and edge-sharing ZnBr₄/Zn(Br,O)₄ tetrahedra of increasing lengths are obtained for (ZnBr₂)_n(18-crown-6)₂. In contrast, [Zn₅Br₉][N(Tf)₂] exhibits a cationic [Zn₅Br₉(18-crown-6)₂]⁺ building unit with distorted tetrahedral, trigonal-bipyramidal and octahedral coordination of Zn²⁺. Besides the coordination of Zn²⁺ to Br⁻, Zn²⁺ is partially coordinated by 18-crown-6 with unusual folding of the crown-ether molecule. In sum, the polynuclear Zn–Br chains can be considered as intermediates between the finite [ZnBr₄]²⁻ anion and the infinite solid . The addition of the Lewis-acid SnBr₄ turned out to be essential for product formation and results in a Br⁻ subtraction from ZnBr₂. The coordination compounds are characterized based on structure analysis, thermogravimetry and energy-dispersive X-ray analysis.