| Abstract
| - Two open-framework ammonium−iron borophosphates, black colored (NH4)0.4FeII0.55FeIII0.5(H2O)2[BP2O8]·0.6H2O (1a) (pale gray colored 1b with a powder X-ray diffraction patternindicating an isotype relationship was also observed) and pale pink colored NH4FeIII[BP2O8(OH)] (2), were synthesized under mild hydrothermal conditions at 180 °C. Their crystalstructures were determined by single-crystal X-ray investigations (hexagonal, P65 (no. 170),a = 9.483(4) Å, c = 15.697(5) Å, V = 1222.5(8) Å3, and Z = 6 for 1a and monoclinic P21/c (no.14), a = 9.370(1) Å, b = 8.309(2) Å, c = 9.680(1) Å, β = 102.05(1)°, V = 737.0(2) Å3, and Z= 4 for 2, respectively). The crystal structure of 1a is characterized by corner-sharing PO4and BO4 tetrahedra, leading to infinite helical {[BP2O8]3-} ribbons, which are connectedby FeII/IIIO4(H2O)2 coordination octahedra. An additional trigonal bipyramidal FeII/IIIO2(H2O)3coordination polyhedron shares common corners and edges with three FeII/IIIO4(H2O)2coordination octahedra, leading to tetrameric units. Helical channels, running along [001],are statistically occupied by H2O molecules and NH4+ ions. The structure of 2 is characterizedby an infinite{[BP2O8(OH)]4-} chain, which is further connected by FeIIIO4(H2O)2 coordination octahedra leading to one-dimensional channels which are occupied by NH4+ ions.The magnetic properties of both compounds are presented. For compound 1a (and 1b), themixed-valence state of iron was confirmed. The susceptibility of compound 2 reveals astronger magnetic interaction and an antiferromagnetic ordering at 17 K.
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