Square versus tetrahedral iron clusters with polyoxometalate ligands

Abstract

Two new insoluble transition metal substituted phosphotungstates, (C₂N₂H₁₀)₁₁[{(B-α-PW₉O₃₄)Fe₃(OH)₃}₄(PO₄)₄Fe]·38H₂O (1) and K₄(C₂N₂H₁₀)₁₂[(α-PW₁₀Fe₂O₃₉)₄]·30H₂O (2), have been isolated by the hydrothermal reaction of [A-α-PW₉O₃₄]⁹⁻, Fe^III ions and ethylenediamine. Compound 1 has a tetrahedral symmetry and contains a Fe₁₃ core built from the assembly of four Fe^III trisubstituted [B-α-PW₉O₃₄]⁹⁻ anions around a central disordered iron ion via four phosphato ligands. The anion in 2 can be described as a square of disubstituted [PW₁₀O₃₇]⁹⁻ anions linked by Fe^III–O–Fe^III bridges. Magnetic measurements performed on 1 and 2 have shown the occurrence of antiferromagnetic interactions between the iron ions and have allowed the coupling constants between the magnetic centers to be determined.