title: Revised Bi/M layered oxo-sulfate (M = Co, Cu): a structural and magnetic study.
abstract: The combination of oxo-bismuthite slabs with counter oxo-anions main often leads to a series of layered Sillen-related compounds. For electroneutrality, it is convenient that the structure incorporates aliovalent cations such as Bi(3+)/M(2+) ions that could be confined either in the Bi/O slabs or in the interleave. In the case of SO4(2-) oxo-anions, only two compounds have been reported for M = Co, Cu, while interesting magnetic topologies emerge in absence of any prior characterization. Our reinvestigation of these systems using crystal growth in Bi2O3 flux led to the full structural characterization of [Bi2CoO3](SO4) (I) and [Bi6.2367Cu1.6O8](SO4)3 (II), which both exhibit pleated [Bi/M/O] slabs running in doubled cells comparatively to previous reports. (I) shows an interesting weak ferromagnetism (∼0.2 μB/Co) below 17 K arising from Dzyaloshinskii-Moriya interactions in Co(2+) zigzag chains, while (II) is essentially a paramagnet despite the presence of Cu2O6 dimers. Finally in the novel [Bi6O6](CoO2)(SO4)2 (III), the Co(2+) ions are ordered with sulfate in the interleaves, leading to a noncentrosymmetric crystal structure.
authors.affiliation: Unité de Catalyse et de Chimie du Solide (UCCS USTL), Université Lille Nord de France, UMR 8181 CNRS , F-59655 Villeneuve d'Ascq, France.
authors.forename: Minfeng
authors.initials: M
authors.lastname: Lü
authors.forename: Marie
authors.initials: M
authors.lastname: Colmont
authors.forename: Houria
authors.initials: H
authors.lastname: Kabbour
authors.forename: Silviu
authors.initials: S
authors.lastname: Colis
authors.forename: Olivier
authors.initials: O
authors.lastname: Mentré