Crystal structure of (NH4)2[FeII5(HPO3)6], a new open-framework phosphite

Abstract

Diammonium hexaphosphitopentaferrate(II), (NH4)2[Fe5(HPO3)6], was synthesized under mild hydrothermal conditions and autogeneous pressure, yielding twinned crystals. The crystal structure exhibits an [FeII5(HPO3)6]2−open framework with NH4+groups as counter-cations. The anionic skeleton is based on (001) sheets of [FeO6] octahedra (one with point-group symmetry 3.. and one with .2.) linked along [001] through [HPO3]2−oxoanions. Each sheet is constructed from 12-membered rings of edge-sharing [FeO6] octahedra, giving rise to channels with a radius ofca3.1 Å in which the disordered NH4+cations are located. The IR spectrum shows vibrational bands typical for phosphite and ammonium groups.