4,4'-bipyMnF3, a modulated hybrid layer structure with 1D magnetic properties
Résumé
4,4′-bipyMnF3 (bipy=bipyridine) has been crystallized from the system MnIII/4,4′-bipy/HF/H2O/methanol/acetone and its crystal structure was determined by single crystal X-ray diffraction at different temperatures: at 295 K the structure is orthorhombic, space group I222, Z=2, a=10.704(1),b=11.384(2) Å, c=3.9413(4) Å, wR2=0.0637, R=0.0244. MnIII is octahedrally coordinated by four F and two N ligands. In the c direction an inorganic FMnFMn- trans-chain is formed, along the b axis bridging by the organic bipy ligands takes place, thus the structure can be classified as a 2D hybrid coordination polymer. The 180° MnFMn bridge angle is symmetry imposed but large anisotropic displacement ellipsoids for the F ligands indicate dynamical disorder of an angular chain. At 240 K and 153 K 1D incommensurate modulated structures (space group I222(00γ)00s) are observed with large variation of the bridge angle down to 149°. Below 100 K the structure can be described as "lock-in phase" with doubled c-axis in the orthorhombic space group P212121 and a bridge angle of 156.4°. 4,4′-bipyMnF3 shows 1D antiferromagnetic properties with an exchange energy along the MnFMn chain of J/k=−11.5 K.