Inorganic–organic hybrid structures: Synthesis, structure and magnetic properties of a new iron oxalatoarsenate, [NH 3(CH 2)CH(NH 3)CH 3] 3[Fe 6(AsO 4) 2(HAsO 4) 6(C 2O 4) 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, [NH 3(CH 2)CH(NH 3)CH 3] 3[Fe 6(AsO 4) 2(HAsO 4) 6(C 2O 4) 3], I. Crystal data: hexagonal, space group = P-3c1, a = 13.9899 ( 12 ) , c = 14.936 ( 3 ) Å , V = 2531.6 ( 5 ) Å 3 . The structure consists of layers of vertex-sharing FeO 6 octahedral and AsO 4 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 FeAsO 4 at ∼650 °C. Magnetic studies reveal that I is antiferromagnetic with T N = 31 K .