Figure 1 Structural unit of (NH4)2[FeII3(H2O)2(P2O7)2], showing the coordination environments of Fe and P atoms. Thermal ellipsoids at the 50% probability level. Green sphere: Fe atom, purple sphere: P atom, red sphere: O atom, blue sphere: N atom, dark grey sphere: H atom. Symmetry codes: (i) x, -y + [{3\over 2}], z + [{1\over 2}]; (ii) -x + 2, -y + 1, -z + 1; (iii) -x + 2, y + [{1\over 2}], -z + [{1\over 2}]; (iv) x, -y + [{1\over 2}], z + [{1\over 2}]  [article HTML]