Single molecule magnets with m-fluorobenzoate and difluoromethylacetate as polar ligands?

Dalton Transactions Pub Date: 2012-11-27 DOI: 10.1039/C2DT32498A

Abstract

Two new single molecule magnets (SMMs), [Mn12O12(CHF2COO)16(H2O)4]·2CH2Cl2·4H2O (1) and [Mn12O12(m-FPhCOO)16(H2O)4]·2(m-FPhCOOH)·7CH2Cl2 (2), based on a disc-shaped {Mn12O12}-framework with difluoromethylacetate (CHF2COO?) and m-fluorobenzoate (m-FPhCOO?) as polar ligands were prepared in CH2Cl2. Structural analyses by X-ray diffraction at 100 K showed orientationally disordered fluorine atoms in the CHF2COO? and m-FPhCOO? ligands of crystals 1 and 2, respectively. In crystal 1, the fluorine atoms at the axial coordination sites of the disc-like {Mn12O12}-framework exhibited large thermal parameters even at 100 K, suggesting that thermally activated rotation of the –CHF2 groups along the C–COO axis occurred in the CHF2COO? ligands. The SMMs behaviors of crystals 1 and 2 showed magnetization hysteresis at 1.8 K and frequency-dependent in-phase and out-of-phase ac magnetic susceptibilities, characteristic of SMMs. Frequency-dependent dielectric responses as well as two Debye-type relaxation processes at ～100 and ～220 K were observed in crystal 1, while such responses were not observed in crystal 2. The activation energy and blocking temperature of the relaxation process for 1 were 12 kJ mol?1 and 48 K, respectively, at ～100 K, whereas those at ～220 K were 66 kJ mol?1 and 153 K, respectively. In 1, the two polarization types at ～100 and ～220 K were associated with thermally activated fluctuations of the hydrogen-bonded crystalline H2O molecules and rotation of the –CHF2 group in the CHF2COO? ligand.

Graphical abstract: Single molecule magnets with m-fluorobenzoate and difluoromethylacetate as polar ligands
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