Mixed inorganic–organic anion frameworks: synthesis and characterisation of [Mn4(PO4)2(C2O4)(H2O)2] and [H3N(CH2)3NH3][Mn2(HPO4)2(C2O4)(H2O)2]

Abstract

Two new three-dimensional manganese phosphate oxalate frameworks have been synthesized and their structures determined by single crystal X-ray diffraction. The compound [Mn₄(PO₄)₂(C₂O₄)(H₂O)₂] 1 is monoclinic, space group P2₁/c, a = 10.263(3), b = 6.526(2), c = 10.082(3) Å and β = 116.84(2)°. MnO₅ and MnO₆ polyhedra share edges to form tetramers, which are further linked by PO₄ tetrahedra to form layers in the bc plane. The layer, which contains an extended array of direct Mn–O–Mn linkages, is in turn linked to neighbouring layers by pillaring bisbidentate oxalate groups. Magnetisation measurements indicate antiferromagnetic interactions, and suggest that the material may be a two dimensional antiferromagnet. Thermogravimetric analysis shows the structure to be stable up to 240 °C. The compound [H₃N(CH₂)₃NH₃][Mn₂(HPO₄)₂(C₂O₄)(H₂O)₂] 2 is monoclinic, space group P2₁/n, a = 5.474(2), b = 15.737(2), c = 9.056(2) Å, β = 93.47(3)°, and includes a disordered 1,3-diaminopropane dication in channels parallel to the a direction. In contrast to 1, no direct Mn–O–Mn linkages occur.