BiMn6PO12, a new bismuth manganese II/III oxyphosphate with an original manganese-oxygen cubic network

A new bismuth manganese oxyphosphate, BiMn6PO12, with an original cubic str ucture has been synthesized by solid state reaction from Bi2O3, MnO2, and ( NH4)(2)HPO4 or BiPO4 and Mn3O4 mixtures. Its crystal structure has been det ermined from single-crystal X-ray diffraction data, It crystallizes in the cubic system with space group Fm (3) over barm and unit cell parameter a = 9.626(1) Angstrom, Z = 4. A full-matrix least-squares refinement yielded R = 0.044 and R-w = 0.045 for 131 independent reflections with I > 2 sigma (I ) collected on a Philips PW100 diffractometer (MoK alpha radiation). The st ructure of BiMn6PO12 is characterized by a three-dimensional network of man ganese-oxygen bonds. The oxygen atoms form a rhombicuboctahedron. The manga nese atoms occupy two-thirds of the square faces of this polyhedron and are at the vertices of cuboctahedra, Manganese and oxygen atoms form a Mn12O24 cage, which constitute the strong basic element of the global building. Th e PO4 tetrahedron is located within this cage and can be moved between two equivalent orientations. The connection between Mn12O24 entities created li ttle cubic holes occupied by bismuth atoms. In this compound all the mangan ese atoms are crystallographically equivalent and the mean oxidation state of manganese is +2.67. A superstructure, which could be due to PO4 orientat ions ordering, was evidenced by an electronic diffraction study. BiMn6PO12 exhibits complicated magnetic behavior with several magnetic transitions bo th in the paramagnetic state and in the low-temperature ordered state. (C) 2001 Academic Press.