Crystal structure of synthetic voltaite (K0.90(NH4)0.10)2(Fe3.1902+Fe1.1243+Mg1.686)(Fe0.9383+Mg0.062)2··(Al0.98Fe0.023+)(SO4)12·18.9H2O

Resumo

Voltaite of the composition [(K_0.90(NH₄)_0.10]₂(Fe_3.190²⁺Fe_1.124³⁺Mg_1.686)(Fe_0.938³⁺Mg_0.062)₂(Al_0.98Fe_0.02³⁺)·(SO₄)₁₂·18.9H₂O* is obtained by treating a polymetallic sample with sulfuric acid. The crystal structure of the substance is formed of (Fe³⁺,Mg)O₆ and (Fe²⁺,Fe³⁺,Mg)O₄(H₂O)₂ octahedra and a (K⁺, NH₄⁺)O₁₂ 12-vertex polyhedron arranged in a three-dimensional framework due to the bridging function of the SO₄²⁻ ion. In the framework voids, [(Fe³⁺,Al)(H₂O)₆]³⁺ cations with aqua ligands are disordered over several positions.