Hydrothermal synthesis, characterization and magnetic properties of three isostructural chain borophosphates; NH4M(III)[BP2O8(OH)] with M = V or Fe and NH4(Fe(III)(0.53)V(III)(0.47))[BP2O8(OH)]

The borophosphates (NH4)M(III)[BP2O8(OH)] with M=V and Fe (1,2) and (NH4)(F e(III)(0.53)V(III)(0.47))[BP2O8(OH)] (3) have been synthesized under hydrot hermal conditions. In addition, the known compound CsFe(III)[BP(2)O8(OH)] ( 4) has also been synthesized in order to compare its magnetic properties wi th those obtained for 1, 2 and 3. These four metal borophosphates are isost ructural and have infinite anionic [BP2O8(OH)](n)(4n-) chains as characteri stic structural building blocks. The octahedrally coordinated transition me tal M(III) ions connect the chains to each other, Hydrogen bonds in the ran ge of 2.89 to 2.97 Angstrom are present between NH4+ cations and the anioni c chains in 1, 2 and 3. Single crystal X-ray diffraction, SEM-EDS analyses, TG/DSC analyses, 4 variable-temperature magnetic susceptibility measuremen ts and FT-IR spectroscopy were used for characterization. Crystal data: Com pounds 1, 2, and 3 crystallize in the monoclinic space group P2(1)/c, with Z = 4. Unit cell parameters: for 1: a = 9.425 (2) Angstrom, b = 8.269(2) An gstrom, c = 9.697(3) Angstrom, beta = 102.26(2)degrees, V = 738.5(2) Angstr om (3), for 2: a = 9.393(3) Angstrom, b = 8.285(2) Angstrom, c = 9.689(2) A ngstrom, beta = 102.07(2)degrees, V = 737.4(4) Angstrom (3), for 3: a = 9.4 04(4) Angstrom, b = 8.316(5) , c = 9.706(2) Angstrom, beta = 102.28(4)degre es, V = 741.6(5) Angstrom (3). TG data for I gave an observed weight loss o f 12% which corresponds well to the release of 1 H2O and 1 NH3 molecule. Fo r 1 and 4, a continuous decrease of T-XM at low temperatures indicates a po ssible antiferromagnetic ordering. Maxima in the magnetic susceptibility da ta were observed for iron borophosphates 2 and 4. (C) 2001 Editions scienti fiques et medicales Elsevier SAS. All rights reserved.