Jahn-Teller ordering in Kagomé-type layers of compounds A2A′Mn3IIIF12 (ARb, Cs; A′Li, Na, K)

摘要: Abstract For a series of new Mn(III) fluorides the crystal structures have been determined by X-ray diffraction on single crystals: Cs 2 LiMn 3 F 12 , space group R Z = (merohedral twin), 7.440(1), c 17.267(3) A 1.95% ; three isostructural triclinic phases, P 1 . NaMn 7.305(1), b 7.512(1), 10.376(2) α 89.89(3)°, β 87.32(3)°, γ 2.75% Rb 7.115(1), 7.482(1), 10.160(2) 89.92(3)°, 86.52(3)°, 89.51(3)°, 2.70% 6.883(1), 7.481(1), 10.194(2) 89.42(3)°, 87.16(3)°, 90.25(3)° 4.87%; monoclinic KMn C2/c, 4, 13.112(3), 7.571(2), 12.672(3) 108.79(3)°, 5.3% All derive from NaAl parent structure and consist [Mn ] layers corner-sharing octahedra Kagome-net-type (3 + 6 units like in hexagonal tungsten bronze layers). The [MnF are strongly elongated Jahn-Teller effect with ratios long to short axes about 1.15. In all oriented within an alternating wind-wheel-like pattern corresponding antiferrodistortive ordering. Thus, MnFMn bridges asymmetric: bridge angles between 136° 141°. Magnetic investigations indicate similar antiferromagnetic exchange interactions ( J k −2.5 K ), but only for compound has 2D 3D ordering found at low temperatures. results discussed context ‘frustrated’ situation Kagome net.