Structure cristalline et proprietes magnetiques de la variete basse temperature TlFeBr3β

DTA and X-Ray studies of TlFeBr₃ show a transition at 384°C. The low temperature phase β-TlFeBr₃ is related to NH₄CdCl₃ and crystallizes in the orthorhombic system with $\text{a}\text{= 9.279(4)}\text{A}\text{?}$, $\text{b}\text{= 3.984(3)}\text{A}\text{?}$, $\text{c}\text{= 15.070(7)}\text{A}\text{?}$, Z = 4. The crystal structure has been determined from 564 independent reflexions. The structure contains FeBr₆ octahedra in which each Fe atom is coordinated to six Br atoms. The FeBr₆ octahedra share vertices to form infinite double chains along the b? axis. This compound behaves paramagnetically above 40 K, with a Curie-Weiss temperature of θ = 12 K and a magnetic moment of μ = 5.59 μB, but becomes antiferromagnetic below 14 K.