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

Abstract

Synthetic analogues of francisite, a mineral of complex formula Cu3Bi(SeO3)2O2X 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 Kagomé type lattice. Preliminary magnetic susceptibility measurements performed on the X = Cl and Br compounds have revealed ferromagnetic-like behaviour below Tc ≈ 24 K. Linear birefringence and X-band Electron Spin Resonance (ESR) data are also presented.