SYNTHESIS, STRUCTURE AND PROPERTIES OF Ba₂Cu₃Cl₂O₄. Zhigang Zou* and Hiroyuki Horiuchi, Mineralogical Institute, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan; Kunihiko Oka and Yoshikazu Nishihara, Electron physics section, Physical science division, Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba Ibaraki 305, Japan. *Present address: Electron physics section, Physical science division, Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba Ibaraki 305, Japan.

Single crystals of a new barium copper oxychloride, Ba₂Cu₃Cl₂O₄ were grown in a Ba(OH)_2- KCl flux. Through the use of single crystal X-ray diffraction method, it was found that the compound has 4/mmm Laue symmetry. The crystal structure was refined in the space group I4/mmm, and lattice constants a=5.519(1), c=13.834(2)Å, Z=2, wR=10.1%. The structure is characterized by infinite layers of [CuO₂]Å which are perpendicular to th e c-axis. The closest Cu-Cu distance is 2.7595(2)Å. The Cu-O-Cu angles are 9 0.64(3) and 178.72(2)0. Ba₂₊ is coordinated to four O_2- ions of a square. The melting temperature of the Ba₂Cu₃Cl₂O₄ is 715.0deg.C. This sample is an insulator. Magnetic properties of the single crystal were also measured.