title: Single molecule magnets with m-fluorobenzoate and difluoromethylacetate as polar ligands.
abstract: Two new single molecule magnets (SMMs), [Mn(12)O(12)(CHF(2)COO)(16)(H(2)O)(4)]·2CH(2)Cl(2)·4H(2)O (1) and [Mn(12)O(12)(m-FPhCOO)(16)(H(2)O)(4)]·2(m-FPhCOOH)·7CH(2)Cl(2) (2), based on a disc-shaped {Mn(12)O(12)}-framework with difluoromethylacetate (CHF(2)COO(-)) and m-fluorobenzoate (m-FPhCOO(-)) as polar ligands were prepared in CH(2)Cl(2). Structural analyses by X-ray diffraction at 100 K showed orientationally disordered fluorine atoms in the CHF(2)COO(-) 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 {Mn(12)O(12)}-framework exhibited large thermal parameters even at 100 K, suggesting that thermally activated rotation of the -CHF(2) groups along the C-COO axis occurred in the CHF(2)COO(-) 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 H(2)O molecules and rotation of the -CHF(2) group in the CHF(2)COO(-) ligand.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan. hoshino@tagen.tohoku.ac.jp
authors.forename: Norihisa
authors.initials: N
authors.lastname: Hoshino
authors.forename: Takuya
authors.initials: T
authors.lastname: Shiga
authors.forename: Hiroki
authors.initials: H
authors.lastname: Oshio
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Akutagawa