Mild hydrothermal synthesis, crystal structure, spectroscopic and magnetic properties of the [M=Fe, x=2.08, y=1.58; M=Co, Ni, x=2.5, y=2] compounds |
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Authors: | Joseba Orive Jos L Mesa Estibaliz Legarra Fernando Plazaola María I Arriortua Tefilo Rojo |
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Institution: | Joseba Orive, José L. Mesa, Estibaliz Legarra, Fernando Plazaola, María I. Arriortua,Teófilo Rojo |
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Abstract: | The M=Fe (1), x=2.08, y=1.58; M=Co (2), x=2.5, y=2; Ni (3), x=2.5, y=2] compounds have been synthesized using mild hydrothermal conditions at 170 °C during five days. Single-crystals of (1) and (2), and polycrystalline sample of (3) were obtained. These isostructural compounds crystallize in the orthorhombic system, space group Aba2, with a=9.9598(2), b=18.8149(4) and c=8.5751(2) Å for (1), a=9.9142(7), b=18.570(1) and c=8.4920(5) Å for (2) and a=9.8038(2), b=18.2453(2) and c=8.4106(1) Å for (3), with Z=8 in the three phases. An X-ray diffraction study reveals that the crystal structure is composed of a three-dimensional skeleton formed by MO5F] and MO4F2] (M=Fe, Co and Ni) octahedra and HPO3] tetrahedra, partially substituted by PO4] tetrahedra in phase (1). The IR spectra show the vibrational modes of the water molecules and those of the (HPO3)2− tetrahedral oxoanions. The thermal study indicates that the limit of thermal stability of these phases is 195 °C for (1) and 315 °C for (2) and (3). The electronic absorption spectroscopy shows the characteristic bands of the Fe(II), Co(II) and Ni(II) high-spin cations in slightly distorted octahedral geometry. Magnetic measurements indicate the existence of global antiferromagnetic interactions between the metallic centers with a ferromagnetic transition in the three compounds at 28, 14 and 21 K for (1), (2) and (3), respectively. Compound (1) exhibits a hysteresis loop with remnant magnetization and coercive field values of 0.72 emu/mol and 880 Oe, respectively. |
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Keywords: | Hydrothermal synthesis Crystal structure Thermal behavior IR UV/Vis and Mö ssbauer spectroscopies Magnetic measurements |
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