Die Kristall- und magnetische Struktur von BaCrF5

Pentafluorochromate(HI), Crystal Structure, Magnetic Structure, Magnetic Susceptibility A single crystal X-ray structure analysis of orthorhombic BaCrFs (a — 1393.8(1), b = 571,1(1), c = 494,7(1) pm), which crystallizes in the structure type of BaGaF5, space group P2i2i2i, yielded Cr-F distances in the range of 187.3 to 194.9 pm, average 190.2 pm. Using powder neutron diffraction data taken at 2.2 K a G-type antiferromagnetic structure with spin alignment along the c direction of the lattice was worked out. Single crystal susceptibility data were consistent with this model and in addition showed a small net moment, probably due to spin canting, to be present below the Neel temperature of TN = 3.4 K. The orientation of this moment along the b axis is in accordance with the space group symmetry as well, chemical and magnetic cell being the same. From powder susceptibility data an exchange energy of —3.74 K (g = 2.02) was obtained by fitting Fisher's model. The low bridging angle of Cr-F-Cr = 137.4° within the eis corner-sharing chain of octahedra is made responsible for the weak antiferromagnetism in BaCrFs, which is compared to that of other chromium(III) fluorides.