Oxohydroxo‐Tellurates(VI) K₂[TeO₂(OH)₄] and K₂[Fe₂TeO₆(OH)₂] ⋅ 2H₂O from Alkaline Hydroflux

Abstract

The ultra‐alkaline conditions of a hydroflux offer the possibility of redox chemistry far from the electrochemical standard potentials. We explored the possibilities of synthesizing tellurium(VI) compounds, using both tellurium(VI) and tellurium(IV) as starting materials. Colorless, block‐shaped crystals of the oxohydroxotellurate(VI) K2[TeO2(OH)4] were synthesized from (NH4)2TeO4 in a KOH hydroflux at 200 °C. In the triclinic crystal structure, [TeO2(OH)4]2− octahedra are connected via hydrogen bonds to form layers, which are separated from each other by potassium cations. Yellow‐colored platelets of the ferrate(III) tellurate(VI) K2[Fe2TeO6(OH)2] ⋅ 2H2O were obtained by oxidation of TeO2 with H2O2 followed by reaction with Fe(NO3)3 ⋅ 9H2O in a KOH hydroflux. In the monoclinic crystal structure, strongly corrugated anionic layers Fe2TeO6(OH)2]2− are covered with water molecules and separated from each other by potassium cations. The octahedrally coordinated iron(III) atoms form a distorted honeycomb network, in which they are antiferromagnetically coupled at room temperature and in external fields up to at least 7 T.