BA5CU4F17CL - A NEW COPPER CHLOROFLUORIDE WITH CHAINS STRUCTURE - STRUCTURAL AND MAGNETIC-PROPERTIES

The study of the Ba-Cu-F-Cl system has shown the existence of a new ph ase with composition Ba5Cu4F17Cl. The structure, with hexagonal symmet ry, has been solved by means of single crystal X-Ray diffraction data analysis. Refinement has been done in the non-centrosymetrical space g roup <P(6)over bar 2m> (n degrees 189), with the following parameters a=10.731(1)Angstrom and c=12.803(2)Angstrom. The reliability factors a re R=0.034 (based on F-0) and wR2=0.093% (based on F-0(2)) for 1908 st ructure factors and 81 parameters. This structure can be described wit h groups of three isolated chains. Each chain is built by the successi on of [CuF6] octahedra, [CuF5] trigonal bipyramid and [CuF4] square pl an. The thermal variation of magnetic susceptibility has been fitted u sing Heisenberg ferromagnetic linear chains model with S=1/2. This fit led to a g-value g=2.25 and J/k=3.9K. Despite the non-linear configur ation of the chains, the results are in good agreement with the experi mental susceptibility. Besides, three dimensional magnetic ordering wa s not observed down to 1.7K.