Synthesis and characterization of layered metal sulfates containing M(μ 3 -OH/F) 2 (M = Mg, Co) diamond chains.

Cobalt and magnesium sulfates of the compositions, [C4 N2 H12 ]2 [Co3 F2 (SO4 )3 (H2 O)2 ], (1) and [NH4 ]2 [Mg3 (OH)2 (SO4 )3 (H2 O)2 ], (2), respectively, have been synthesized under hydro/solvothermal conditions, and are characterized by IR spectra, elemental analysis, powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and X-ray single-crystal diffraction. 1 and 2 crystallized in the orthorhombic space groups Pnma and Cmc2 respectively. While 1 is templated by the organic piperazinium cation, 2 is obtained in the presence of ammonium ions. The layered structures are formed by the diamond chains comprising of M3 (μ3 -OH/F)2 units (M = Co: 1, Mg: 2). Magnetic studies of 1 reveal its ferromagnetic nature with a transition at 10.8 K and show it does not exhibit spin-glass freezing. Isothermal magnetization shows a hysteresis loop at 2.5 K with a coercive field of 1200 Oe and remnant magnetization of 0.1μB . A sharp λ-like anomaly is also seen in the heat capacity curve, favoring long range magnetic ordering below Tc .