Synthesis, Structure, and Magnetic Behavior of La5Re3MnO16: A New Perovskite-like Material

Single crystals of La5Re3MnO16 have been grown and characterized by X-ray diffraction. The crystal structure was found to be of triclinic symmetry, but with strong monoclinic pseudosymmetry and related to the structure of La5Mo4O16 (M. Ledesert, Ph. Labbe, W. H. McCarroll, H. Leligny, and B. Raveau, J. Solid State Chem. 105, 143 (1993)). The atomic parameters were refined in the unconventional C-1 space group, which is derived from C2/m by suppressing the two-fold axis. The structure is similar to that of the perovskites, consisting of layers of slightly distorted corner-sharing ReO6 and MnO6 octahedra. The layers are connected by Re2O10 units which consist of distorted edge-sharing ReO6 octahedra. The Re–Re bond in these units is found to be unusually short (2.4068(5) ?). The La atoms are in three different crystallographic environments. La(1) and La(2) are eight- and seven-fold coordinated, respectively, and lie in chains in the ReO6 and MnO6 network. La(3) has a distorted cubic coordination in a cage formed by the Re2O10 units. Bond valence sums are consistent with Mn2+ and Re5+. Powder samples have also been synthesized for magnetic susceptibility measurements. The magnetic properties are complex. Curie–Weiss behavior occurs only in the range 400–600 K giving C=4.43 emu·K/mol and =-48(5) K, consistent with Mn2+ as the only magnetic ion and net antiferromagnetic coupling. A transition to a long-range ordered state occurs below 160 K and a field-induced irreversibility sets in below 50 K. Isothermal magnetization-field data imply a complex H–T phase diagram and magnetic structure.