K₂[Fe^II ₃(P₂O₇)₂(H₂O)₂]

Abstract

The title compound, dipotassium diaquabis(diphosphato)triferrate(II), K 2 [Fe II 3 (P 2 O 7 ) 2 (H 2 O) 2 ], was synthesized under solvothermal conditions. The crystal structure is isotypic with its Co analogue. In the structure, there are two crystallographically distinct Fe positions; one lies on an inversion center, the other on a general position. The first Fe 2+ cation adopts a regular octahedral coordination with six O atoms, whereas the other is coordinated by five O atoms and a water molecule. The [FeO 6 ] octahedron shares its trans -edges with an adjacent [FeO 5 (H 2 O)] octahedron; in turn, the [FeO 5 (H 2 O)] octahedron shares skew-edges with a neighbouring [FeO 6 ] octahedron and an [FeO 5 (H 2 O)] octahedron, resulting in a zigzag octahedral chain running along [001]. The zigzag chains are linked to each other by the P 2 O 7 diphosphate groups, leading to a corrugated iron diphosphate layer, [Fe 3 (P 2 O 7 ) 2 (H 2 O) 2 ] 2− , parallel to (100). The interlayer space is occupied by K + cations, which adopt an eight-coordination to seven O atoms and one water molecule from a neighbouring iron diphosphate layer. Thus, the K + ions not only compensate the negative charge of the layer but also link the layers into a network structure.