4,4'-bipyMnF_3, a modulated hybrid layer structure with 1D magnetic properties

摘要

4,4'-bipyMnF_3(bipy-bipyridine) has been crystallized from the system Mn~(III)/4,4'-bipy/HF/H_2O/methanol/acetone and its crystal structure was determined by single crystal X-ray diffraction at different temperatures: at 295K the structure is orthorhombic, space group I222, Z=2, a=10.704(1), b=11.384(2)A, c=3.9413(4)A, wR_2=0.0637, R=0.0244. Mn~(III) is octahedrally coordinated by four F and two N ligands. In the c direction an inorganic F-Mn-F-Mn-trans-chain is formed, along the b axis bridging by the organic bipy ligands takes place, thus the structure can b classified as a 2D hybrid coordination polymer. The 180 deg Mn-F-Mn bridge angle is symmetry imposed but large anisotropic displacement ellipsoids for the F ligands indicate dynamical disorder of an angular chain. At 240K and 153 K 1D incommensurate modulated structures (space group I222(00 gamma)00s) are observed with large variation of the bridge angle down to 149 deg. Below 100K the structure can be described as "lock-in phase" with doubled c-axis in the orthorhombic space group P2_12_12_1 and a bridge angle of 156.4 deg. 4,4'-bipyMnF_3 shows 1D antiferromagnetic properties with an exchange energy along the Mn-F-Mn chain of J/k=-11.5K.