Syntheses, crystal structures and magnetic properties of francisite compounds Cu3Bi(SeO3)(2)O2X (X = Cl, Br and I)

Synthetic analogues of francisite, a mineral of complex formula Cu3Bi(SeO3)(2)O2X with X = Cl, Br, I, have been obtained by solid state reaction. Contrary to the previous structure description, the framework can be better described as formed of copper(II)-oxygen layers linked together in the [001] direction by long bismuth-oxygen bonds. These layers are formed by a hexagonal network of [CuO4] square plane sharing apices whose geometry is reminiscent of a Kagome type lattice. Preliminary magnetic susceptibility measurements performed on the X = Cl and Br compounds have revealed ferromagnetic-like behaviour below T-c approximate to 24 K. Linear birefringence and X-band Electron Spin Resonance (ESR) data are also presented.