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