Three mononuclear model complexes with pentagonal bipyramidal geometry, [MII(L-N3O2)(MeCN)2][BPh4]2 (M = Fe, 1; Co, 2; Ni, 3) were isolated and found to exhibit large uniaxial (1 and 3) and easy-plane (2) magnetic anisotropy, respectively.
Two mononuclear trigonal prismatic Co(II) complexes [Co(tppm*)][BPh 4 ] 2 (1) and [Co(hpy)][BPh 4 ] 2 •3CH 2 Cl 2(2) (tppm* = 6,6′,6″-(methoxymethanetriyl)tris(2-(1H-pyrazol-1yl)pyridine; hpy = tris(2,2′-bipyrid-6-yl)methanol) were synthesized by incorporating the Co(II) ions in two pocketing tripodal hexadentate ligands. Magnetic studies indicate similar uniaxial magnetic anisotropy while having distinct dynamic magnetic properties for two complexes, of which 1 exhibits clear hysteresis loops and Orbach process governed magnetic relaxation with an effective energy barrier (U eff ) of 192 cm −1 , among the best examples in transition metallic SIMs, about 10 times larger than that of 2 (U eff = 20 cm −1 , extracted by fitting the data to an Orbach relaxation process but there is no real state at this energy). Such pronounced difference is ascribed to the dominant Raman process and quantum tunneling of magnetization (QTM) in 2 owing to the structural distortion and symmetry breaking, indicated by a nearly perfect trigonal prismatic geometry (D 3 local symmetry) for 1 and a more distorted configuration for 2 (C 3 local symmetry). Ab initio calculations predict strong axial anisotropy for 1 with minimal QTM probability, with the transverse component of anisotropy being estimated to be much higher for 2 than 1, leading to a 10-fold lower U eff value than 1.
A new tripodal hexadentate ligand of tris[6-(1H-pyrazol-1-yl)pyridin-2-yl]methanol (tppm) was synthesized and explored for constructing the trigonal-prismatic cobalt(II) complex [Co(tppm)]- 1). Magnetic study showed that 1 exhibited large uniaxial magnetic anisotropy with a zerofield-splitting parameter of −80.7 cm −1 and typical singlemolecule-magnet behavior.
Taking advantage
of a rigid tetradentate ligand of bis(pyrazoly)(3-pyrazolypyridinyl)methane
(PyPz3) and the [CuII(opba)]2– unit [opba4– = o-phenylenebis(oxamato)],
the trinuclear complex [{CoII(PyPz3)}2CuII(opba)][ClO4]2·5MeCN·MeOH
(1) was constructed, in which the CoII centers
adopt a trigonal-prismatic geometry, while considerable intramolecular
magnetic coupling was successfully introduced through the oxamido
bridges, representing another very first example of single-molecule
magnets marrying both selected coordination geometry and magnetic
exchanges.
Two lanthanide single molecule magnets (SMMs) of [Dy3(μ3-OH)(HL-1)3(H2O)3](NO3)2·CH3CN·CH3OH (1, H3L-1 = (E)-3-(((8-hydroxyquinolin-2-yl)methylene)amino)propane-1,2-diol and [Dy6(μ3-OH)4(H2L-2)4(HL-2)2(L-2)2] (2, H3L-2 = (E)-2-hydroxy-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide) were synthesized and characterized structurally and magnetically. Complex 1 contains a triangle...
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