Inorganic–organic hybrid structures: Synthesis, structure and magnetic properties of a new iron oxalatoarsenate, [NH3(CH2)CH(NH3)CH3]3[Fe6(AsO4)2(HAsO4)6(C2O4)3]

A hydrothermal reaction of a mixture of iron oxalate, arsenic acid, 1,2-diaminopropane and water at 150 °C gave rise to a new three-dimensional iron oxalatoarsenate, [NH3(CH2)CH(NH3)CH3]3[Fe6(AsO4)2(HAsO4)6(C2O4)3], I. Crystal data: hexagonal, space group = P-3c1, a=13.9899(12)a=13.9899(12), c=14.936(3) Åc=14.936(3) Å, V=2531.6(5) Å3V=2531.6(5) Å3. The structure consists of layers of vertex-sharing FeO6 octahedral and AsO4 tetrahedral units that form 12-membered apertures. The layers are connected together by the oxalate units, forming a uniform one-dimensional channel that is occupied by protonated amine molecules. Variable temperature powder XRD studies indicates that I loses crystallinity at ∼300 °C forming an amorphous phase that gives way to crystalline FeAsO4 at ∼650 °C. Magnetic studies reveal that I is antiferromagnetic with TN=31 KTN=31 K.

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