Generating Zintl Anions: Homoatomic Polyanions of Group 15 Elements by Oxidative Coupling of Smaller Anions or Direct Reduction of the Elements in Liquid Ammonia

Abstract

The new polyphosphorus Zintl anion P₂₂ ⁴⁻ has been synthesised by combining two P₁₁ ³⁻ anions by oxidation with Br₂I⁻ in liquid ammonia. The single crystal structure analysis shows that P₂₂ ⁴⁻ consists of two trishomocubane-like cages connected by a single bond. While the former method makes use of pre-formed Zintl anions extracted from solids, the second route presented involves direct reduction of the elements with the expanded metal Li(NH₃)₄. Reaction of Li(NH₃)₄ with P, As, and Sb yields [Li(NH₃)₄]4P₁₄ , [Li(NH₃)₄]₃As₇ · NH₃ and [Li(NH₃)₄]₃[Li₂(NH₃)₂Sb₅] · 2 NH₃. The Sb compound contains the new Zintl anion cyclo-Sb₅ ⁵⁻ , which is stabilised in the ion complex (Li₂(NH₃)₂Sb₅)³⁻.

Keywords::

• Zintl ions
• homoatomic polyanions
• expanded metals;