A New Family of 1D Exchange Biased Heterometal Single-Molecule Magnets: Observation of Pronounced Quantum Tunneling Steps in the Hysteresis Loops of Quasi-Linear {Mn2Ni3} Clusters
| Autor: | Paul Müller, Vladislav Kataev, Bernd Büchner, Rüdiger Klingeler, Klaus Gieb, Animesh Das, Sebastian Dechert, Yulia Krupskaya, Serhiy Demeshko, Franc Meyer |
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| Rok vydání: | 2011 |
| Předmět: |
010405 organic chemistry
Hydrogen bond Chemistry Relaxation (NMR) General Chemistry 010402 general chemistry 01 natural sciences Biochemistry Catalysis 0104 chemical sciences 3. Good health law.invention Crystallography Magnetization Colloid and Surface Chemistry Ferromagnetism law Intramolecular force Molecule Ground state Electron paramagnetic resonance |
| Zdroj: | Journal of the American Chemical Society. 133:3433-3443 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja108740c |
| Popis: | First members of a new family of heterometallic Mn/Ni complexes [Mn(2)Ni(3)X(2)L(4)(LH)(2)(H(2)O)(2)] (X = Cl: 1; X = Br: 2) with the new ligand 2-{3-(2-hydroxyphenyl)-1H-pyrazol-1-yl}ethanol (H(2)L) have been synthesized, and single crystals obtained from CH(2)Cl(2) solutions have been characterized crystallographically. The molecular structures feature a quasi-linear Mn(III)-Ni(II)-Ni(II)-Ni(II)-Mn(III) core with six-coordinate metal ions, where elongated axes of all the distorted octahedral coordination polyhedra are aligned parallel and are fixed with respect to each other by intramolecular hydrogen bonds. 1 and 2 exhibit quite strong ferromagnetic exchange interactions throughout (J(Mn-Ni) ≈ 40 K (1) or 42 K (2); J(Ni-Ni) ≈ 22 K (1) or 18 K (2)) that lead to an S(tot) = 7 ground state, and a sizable uniaxial magnetoanisotropy with D(mol) values -0.55 K (1) and -0.45 K (2). These values are directly derived also from frequency- and temperature-dependent high-field EPR spectra. Slow relaxation of the magnetization at low temperatures and single-molecule magnet (SMM) behavior are evident from frequency-dependent peaks in the out-of-phase ac susceptibilities and magnetization versus dc field measurements, with significant energy barriers to spin reversal U(eff) = 27 K (1) and 22 K (2). Pronounced quantum tunnelling steps are observed in the hysteresis loops of the temperature- and scan rate-dependent magnetization data, but with the first relaxation step shifted above (1) or below (2) the zero crossing of the magnetic field, despite the very similar molecular structures. The different behavior of 1 and 2 is interpreted in terms of antiferromagnetic (1) or ferromagnetic (2) intermolecular interactions, which are discussed in view of the subtle differences of intermolecular contacts within the crystal lattice. |
| Databáze: | OpenAIRE |
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