| Abstract
| - A new molecule-based weak ferromagnet of formula Fe[C6H5PO3]·H2O was synthesized. It was characterized bythermogravimetric analysis and UV−visible and infrared spectroscopy, and the magnetic properties were studiedusing a superconducting quantum interference device magnetometer. The crystal structure of the compound wasdetermined “ab initio” from X-ray powder diffraction data and refined by the Rietveld method. The crystals ofFe[C6H5PO3]·H2O are orthorhombic, space group Pmn21, with a = 5.668(8) Å, b = 14.453(2) Å, c = 4.893(7)Å, and Z = 2. The title compound is isostructural with the previously reported lamellar M[C6H5PO3]·H2O, M =Mn(II), Zn(II), and Cd(II). The inorganic layers are made of Fe(II) ions octahedrally coordinated by five phosphonateoxygen atoms and one from oxygen of the water molecule. These layers are then separated by bilayers of thephenyl groups, and van der Waals contacts are established between them. The refinement has shown that thephenyl rings are disordered in the lattice. The oxidation state of the metal ion is +2, and the electronic configurationis d6(S = 2) high-spin, as determined from dc magnetic susceptibility measurements from 150 K to roomtemperature. Below 100 K, the magnetic moment of Fe[C6H5PO3]·H2O rises rapidly to a maximum at TN = 21.5K, and then it decreases again. The peak at TN is associated with the 3D antiferromagnetic long-range ordering.Below the critical temperature, the title compound behaves as a “weak” ferromagnet, which represents the thirdtype of magnetic materials characterized by having a finite zero-field magnetization, ferromagnets and ferrimagnetsbeing the other two types. The large coercive field (i.e., 6400 G) observed in the hysteresis loop at T = 10 K israre in molecule-based materials; it can be ascribed to a pronounced spin−orbit coupling for the 5T2g groundstate of the Fe(II) ion in the octahedral environment.
- The title compound has a layered structure. The inorganic layers are made of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from the oxygen of the water molecule. The layers are separated by bilayers of the phenyl groups. The compound orders antiferromagnetically at T = 21.5 K. Below the critical temperature TN, it behaves as a “weak” ferromagnet and it is characterized by having a large coercive field.
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