Abstract
For a series of new Mn(III) fluorides the crystal structures have been determined by X-ray diffraction on single crystals: Cs2LiMn3F12, space group R3̄, Z = 3 (merohedral twin), a = 7.440(1), c = 17.267(3) Å, R = 1.95%; three isostructural triclinic phases, space group P1̄, Z = 2, Cs2NaMn3F12, a = 7.305(1), b = 7.512(1), c = 10.376(2) Å, α = 89.89(3)°, β = 87.32(3)°, γ = 89.89(3)°, R = 2.75%; Rb2NaMn3F12, a = 7.115(1), b = 7.482(1), c = 10.160(2) Å, α = 89.92(3)°, β = 86.52(3)°, γ = 89.51(3)°, R = 2.70%; Rb2LiMn3F12, a = 6.883(1), b = 7.481(1), c = 10.194(2) Å, α = 89.42(3)°, β = 87.16(3)°, γ = 90.25(3)°. R = 4.87%; monoclinic Cs2KMn3F12, space group C2/c, Z = 4, a = 13.112(3), b = 7.571(2), c = 12.672(3) Å, β = 108.79(3)°, R = 5.3%. All structures derive from the Cs2NaAl3F12 parent structure and consist of [Mn3F12] layers of corner-sharing octahedra of the Kagomé-net-type (3+6 octahedra units like in the hexagonal tungsten bronze layers). The [MnF6] 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 Mn-F-Mn bridges are asymmetric; the bridge angles are between 136° and 141°. Magnetic investigations of Cs2NaMn3F12 and Cs2KMn3F12 indicate similar antiferromagnetic exchange interactions (J/k = -2.5 K), but only for the Cs2K 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.
Original language | English (US) |
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Pages (from-to) | 155-165 |
Number of pages | 11 |
Journal | Journal of Alloys and Compounds |
Volume | 246 |
Issue number | 1-2 |
DOIs | |
State | Published - Jan 15 1997 |
Externally published | Yes |
Keywords
- Crystal structures
- Fluoromanganates(III)
- Jahn-Teller ordering
- Magnetism
- Manganese(III)
ASJC Scopus subject areas
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry