Open-framework borophosphates: (NH4)(0.4)(Fe0.55Fe0.5III)-Fe-II(H2O)(2)[BP2O8]center dot 0.6H(2)O and NH4FeIII[BP2O8(OH)]

Two open-framework ammonium-iron borophosphates, black colored (NH4)(0.4)(F e0.55Fe0.5III)-Fe-II(H2O)(2)[BP2O8].0.6H(2)O (1a) (pale gray colored 1b wit h a powder X-ray diffraction pattern indicating an isotype relationship was also observed) and pale pink colored NH4FeIII[BP2O8(OH)] (2), were synthes ized under mild hydrothermal conditions at 180 degreesC. Their crystal stru ctures were determined by single-crystal X-ray investigations (hexagonal, P 6(5) (no. 170), a = 9.483(4) Angstrom, c = 15.697(5) Angstrom, V = 1222.5(8 ) Angstrom (3), and Z = 6 for 1a and monoclinic P2(1)/c (no. 14), a = 9.370 (1) Angstrom, b = 8.309(2) Angstrom, c = 9.680(1) Angstrom, beta = 102.05(1 )degrees, V = 737.0(2) Angstrom (3), and Z = 4 for 2, respectively). The cr ystal structure of 1a is characterized by corner-sharing PO4 and BO4 tetrah edra, leading to infinite helical (1)(infinity){[BP2O8](3-)} ribbons, which are connected by (FeO4)-O-II/III(H2O)(2) coordination octahedra. An additi onal trigonal bipyramidal (FeO2)-O-II/III(H2O)(3) coordination polyhedron s hares common corners and edges with three (FeO4)-O-II/III(H2O)(2) coordinat ion octahedra, leading to tetrameric units. Helical channels, running along [001], are statistically occupied by H2O molecules and NH4+ ions. The stru cture of 2 is characterized by an infinite (1)(infinity){[BP2O8(OH)](4-)} c hain, which is further connected by (FeO4)-O-III(H2O)(2) coordination octah edra leading to one-dimensional channels which are occupied by NH4+ ions. T he magnetic properties of both compounds are presented. For compound 1a (an d 1b), the mixed-valence state of iron was confirmed. The susceptibility of compound 2 reveals a stronger magnetic interaction and an antiferromagneti c ordering at 17 K.