Synthesis, structure and magnetic behavior of iron arsenites with hierarchical magnetic units

Abstract

The standard redox potentials of the Fe³⁺/Fe²⁺ (+0.77 V) and H₃AsO₄/H₃AsO₃ (+0.56 V) stabilize the easy crystallization of ferric arsenates. However, activating solvothermal reactions with a reducing agent such as hydrazine or ethanol may destabilize the solid compounds towards ferric, ferrous or mixed Fe^2+/3+ arsenites. Few of them have been reported and in this work we have prepared four new members with various counter cations (Ba²⁺) or anions (OH⁻, Cl⁻) and various iron valence. The versatile condensation of ortho-arsenites (AsO₃²⁻) into pyro–(As₂O₅⁴⁻⁾, rings or meta-arsenites favours the creation of efficient spacers, able to tune the magnetic dimensionality of the iron-based framework. These four new members cover from 0D (paramagnetic Ba₂Fe^II(As³⁺₃O₆)₂·H₂O), 1D (S = 5/2 ladders in BaFe^III₂(As₂O₅)(AsO₃)(OH)), 2D (layers of S = 5/2 dimers in Ba₂Fe^III₂O(As₂O₅)₂, up to 3D (T_N = 97 K in Fe₃^2.66+(As₂O₅)(AsO₃)Cl with charge ordering) topologies. Their magnetic properties are analysed by means of combined structural, experimental results and ab initio calculations.