Open-Framework Borophosphates: (NH4)0.4FeII0.55FeIII0.5(H2O)2[BP2O8]·0.6H2O and NH4FeIII[BP2O8(OH)]

Two open-framework ammonium−iron borophosphates, black colored (NH 4 ) 0.4 Fe II 0.55 Fe III 0.5 (H 2 O) 2 [BP 2 O 8 ]·0.6H 2 O ( 1a ) (pale gray colored 1b with a powder X-ray diffraction pattern indicating an isotype relationship was also observed) and pale pink colored NH 4 Fe III [BP 2 O 8 (OH)] ( 2 ), were synthesized under mild hydrothermal conditions at 180 °C. Their crystal structures were determined by single-crystal X-ray investigations (hexagonal, P 6 5 (no. 170), a = 9.483(4) Å, c = 15.697(5) Å, V = 1222.5(8) Å 3, and Z = 6 for 1a and monoclinic P 2 1 / 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) Å 3, and Z = 4 for 2, respectively). The crystal structure of 1a is characterized by corner-sharing PO 4 and BO 4 tetrahedra, leading to infinite helical {[BP 2 O 8 ] 3 - } ribbons, which are connected by Fe II/III O 4 (H 2 O) 2 coordination octahedra. An additional trigonal bipyramidal Fe II/III O 2 (H 2 O) 3 coordination polyhedron shares common corners and edges with three Fe II/III O 4 (H 2 O) 2 coordination octahedra, leading to tetrameric units. Helical channels, running along [001], are statistically occupied by H 2 O molecules and NH 4 + ions. The structure of 2 is characterized by an infinite {[BP 2 O 8 (OH)] 4 - } chain, which is further connected by Fe III O 4 (H 2 O) 2 coordination octahedra leading to one-dimensional channels which are occupied by NH 4 + ions. The magnetic properties of both compounds are presented. For compound 1a (and 1b ), the mixed-valence state of iron was confirmed. The susceptibility of compound 2 reveals a stronger magnetic interaction and an antiferromagnetic ordering at 17 K.