ON THE COMPOUND SR7MN4O15 AND STRUCTURE RELATIONS TO SR2MNO4 AND ALPHA-SRMNO3

The "compound" hitherto described as a alpha modification of Sr2MnO4 is shown to consist of a mixture of SrO and the new monoclinic compound Sr7Mn4O15 crystallizing in the space group P2(1)/c, a = 681.78(6), b = 962.24(8), c = 1038.0(1) pm, beta = 91.886(7)-degrees, Z = 2. Up to 0.3 mm long black crystals were grown from prereacted Sr7Mn4O15, SrO, and SrCl2 at 1 350-degrees-C in a sealed platinum tube under argon. Its structure is related to alpha-SrMnO3. It contains layers of corner-shared double octahedra [O2/2OMnO3MnO2O1/2]7- parallel to (100). Above 100 K the magnetism of Sr7Mn4O15 follows the Curie Weiss law with THETA almost-equal-to -426K and a moment mu(eff) = 3.62 mu(B) corresponding Mn4+.