Synthesis, X-ray powder structure, and magnetic properties of the new, weak ferromagnet iron(II) phenylphosphonate

A new molecule-based weak ferromagnet of formula Fe[C6H5PO3]. H2O was synth esized It was characterized by thermogravimetric analysis and UV-visible an d infrared spectroscopy, and the magnetic properties were studied using a s uperconducting quantum interference device magnetometer. The crystal struct ure of the compound was determined "ab initio" from X-ray powder diffractio n data and refined by the Rietveld method. The crystals of Fe[C6H5PO3]. H2O are orthorhombic, space group Pmn2(1), with a = 5.668(8) Angstrom, b = 14. 453(2) Angstrom, c = 4.893(7) Angstrom, and Z = 2. The title compound is is ostructural with the previously reported lamellar M[C6H5PO3]. H2O, M = Mn(I I), Zn(II), and Cd(II). The inorganic layers are made of Fe(II) ions octahe drally coordinated by dye phosphonate oxygen atoms and one from oxygen of t he water molecule. These layers are then separated by bilayers of the pheny l groups, and van der Waals contacts are established between them. The refi nement has shown that the phenyl rings are disordered in the lattice. The o xidation state of the metal ion is +2, and the electronic configuration is d(6) (S = 2) high-spin, as determined from de magnetic susceptibility measu rements from 150 K to room temperature. Below 100 K, the magnetic moment of Fe[C6H5PO3]. H2O rises rapidly to a maximum at T-N = 21.5 K, and then it d ecreases again. The peak at T-N is associated with the 3D antiferromagnetic long-range ordering. Below the critical temperature, the title compound be haves as a "weak" ferromagnet, which represents the third type of magnetic materials characterized by having a finite zero-field magnetization, ferrom agnets and ferrimagnets being the other two types. The large coercive field (i.e., 6400 G) observed in the hysteresis loop at T = 10 K is rare in mole cule-based materials; it can be ascribed to a pronounced spin-orbit couplin g for the T-5(2g) ground state of the Fe(II) ion in the octahedral environm ent.