Novel transition metal oxalatophosphates with a two-dimensional honeycomb structure: (H₃TREN)[M₂(HPO₄)(C ₂O₄)_2.5]·3H₂O (M = Mn ^II and Fe^II, TREN = tris(2-aminoethyl)amine)

Two new layered transition metal oxalatophosphates, (H ₃TREN)-[M₂(HPO₄)(O₂O ₄)_2.5]·3H₂O (M = Mn^II and Fe^II), have been synthesized by hydrothermal methods in the presence of a structure-directing organic amine, tris(2-aminoethyl)amine, and characterized by single-crystal X-ray diffraction and magnetic susceptibility. They are the first metal oxalatophosphates which adopt a two-dimensional honeycomb structure with the organic cations and water molecules intercalated in between. Within a layer, there are 12-membered pores made from 6 Mn, 1 phosphate, and 5 oxalate units. Measurements of field dependence of magnetization and variable-temperature susceptibilities under different fields were performed on a polycrystalline sample of the manganese compound. The results indicate a phase transition from a paramagnetic to an antiferromagnetic coupled state at about 12 K. Crystal data for the manganese compound follow: triclinic, space group P1̄ (No. 2), a = 8.8385(6) Å, b = 9.0586(6) Å, c = 16.020(1) Å, α = 77.616(1)°, β = 83.359(1)°, γ = 68.251(1)°, and Z = 2. Crystal data for the iron compound are the same as those for the manganese compound except a = 8.7776(9) Å, b = 8.9257(9) Å, c = 15.884(2) Å, α = 78.630(2)°, β = 84.018(2)°, and γ = 67.372(2)°.