Crystal structure and magnetic properties of Co7(TeO3)4Br6—a new cobalt tellurite bromide

The crystal structure of the new compound Co7(TeO3)4Br6 is described together with the magnetic properties. The new compound crystallizes in the monoclinic space group C2/c with the unit cell parameters a=20.6532(5) Åa=20.6532(5) Å, b=8.6533(2) Åb=8.6533(2) Å, c=14.7262(5) Åc=14.7262(5) Å, β=124.897(3)°β=124.897(3)°, Z=4Z=4. The crystal structure was solved from single crystal data, R=0.0242R=0.0242. The structure can be considered as layered and the building units are [CoO4Br2] and [CoO2Br4] octahedra and [TeO3E] tetrahedra, E being the 5s2 lone pair on the Te(IV) ions. The magnetic properties of the compound are characterised by antiferromagnetic correlations at high temperatures, strong deviation from the Curie–Weiss behaviour in a broad intermediate temperature range and long range magnetic ordering setting-in at low temperatures. Magnetic ordering takes place in stages, being represented by two susceptibility anomalies, at TN=33 KTN=33 K and TC=27 KTC=27 K. The magnetic transition at TCTC is ferromagnetic (or ferrimagnetic) in character.

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