Synthesis, structural relationships and magnetic properties of new amine-templated manganese(II) phosphate oxalate framework materials

Three novel three-dimensional framework materials in the manganese(II)–phosphate–oxalate system have been prepared hydrothermally using organic amines as structure-directing agents. [H3NC6H10NH3][Mn2(HPO4)2(C2O4)(H2O)2] 1 and [H3N(CH2)2NH3][Mn2(HPO4)2(C2O4)(H2O)2] 2 have related, but not isomorphous, structures based on layers of vertex-sharing MnO6 and PO4 polyhedra linked by bridging oxalate groups. [H3N(CH2)2NH3][Mn4(HPO4)2(C2O4)3(H2O)2]·2H2O 3 has a very different structure composed of edge-sharing dimeric MnO6 units linked into chains by PO4 groups, and into a 3-D framework by oxalate units. 3 can be topotactically dehydrated, with loss of both extra-framework and co-ordinated water, to produce a new phase 4. The magnetic susceptibilities of phases 1, 3 and 4 all show Curie–Weiss behaviour above about 50 K, and a maximum in the susceptibility curve in the vicinity of 7–12 K, indicating significant antiferromagnetic exchange. Structural relationships to other phosphate–oxalate frameworks are discussed.