PRELIMINARY CRYSTAL-STRUCTURE OF MIXED-VALENCY SR4NI3O9, THE ACTUAL FORMULA OF THE SO-CALLED SR5NI4O11

A crystal structure investigation of the so-called Sr5Ni4O11 from single-crystal X-ray data has shown that the composition of this oxide is in fact close to Sr4Ni3O9. The structure has been solved in the trigonal P321 space group. The final refinement gave an R factor of 0.045 for 512 independent reflections. The structure contains NiO3 chains with two NiO6 octahedra and one NiO6 trigonal prism alternating and sharing faces. The chains run along the three-fold axis and are connected by Sr ions. The Ni-O distances seem to indicate a possible repartition of Ni(IV) in the octahedral sites and Ni(II) in the trigonal prisms.