Synthesis and characterization of layered metal sulfates containing M II3(μ3-OH/F)2(M = Mg, Co) diamond chains

Abstract

Cobalt and magnesium sulfates of the compositions, [C₄N₂H₁₂]₂[Co₃F₂(SO₄)₃(H₂O)₂], (1) and [NH₄]₂[Mg₃(OH)₂(SO₄)₃(H₂O)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 0.1μ_B. A sharp λ-like anomaly is also seen in the heat capacity curve, favoring long range magnetic ordering below T_c.