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Two lanthanide complexes with formulae [DyIII(LN5)(pentafluoro-PhO)3] (1) and [DyIII(LN5)(2,6-difluoro-PhO)2](BPh4) (2) (LN5 = 2,14-dimethyl-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadecal (19),2,13,15,17-pentaene) were structurally and magnetically characterized. DyIII ions lie in the cavity of a five coordinate nitrogen macrocycle, and in combination with the introduction of multi-fluorinated monodentate phenoxyl coligands a high axiality coordination symmetry is built. Using the pentafluorophenol co-ligand, complex 1 with a D2d coordination environment, is obtained and displays moderate single-molecule magnets (SMMs) behavior. When difluorophenol co-ligands were used, a higher local axisymmetric pentagonal bipyramidal coordination geometry was observed in complex 2, which displays apparent slow magnetic relaxation behavior with a hysteresis temperature of up to 5 K. Further magnetic studies of diluted samples combined with ab initio calculations indicate that the high axiality plays a crucial role in suppressing quantum tunneling of magnetization (QTM) and consequently results in good slow magnetic relaxation behavior. Different fluoro-substituted phenoxyl co-ligands have phenoloxy oxygen atoms with different electrostatic potentials as well as a different number of phenoloxy coligands along the magnetic axis, resulting in different ligand field strengths and coordination symmetries. [ABSTRACT FROM AUTHOR]

Synthesis of 3d–4f single molecule magnets (SMMs) with novel topologies and exploration of the magnetic relaxation mechanism of SMMs have continuously received considerable attention because high performance SMMs could be obtained. In this work, we selected N-3-methoxysalicylidene-2-amino-3-hydroxypyridine (H2L) and di-2-pyridyl ketone (dpk) for reaction with Ni(NO3)2·6H2O, Dy(NO3)3·5H2O and trimethylamine in a CH3OH solution, and a novel Ni4Dy4 complex, [Ni4Dy4(L)6(L′)2{(py)2C(OCH3)O}2(μ3-CO3)2(CH3OH)2]·10CH3OH·13H2O (1, (py)2C(OCH3)(OH) = the hemiacetal form of dpk), was obtained. The magnetic diluted complex, [Ni4Y3.91Dy0.09(L)6(L′)2{(py)2C(OCH3)O}2(μ3-CO3)2(CH3OH)2]·10CH3OH·12H2O (2), and the Y analogue of 1, [Ni4Y4(L)6(L′)2{(py)2C(OCH3)O}2(μ3-CO3)2(CH3OH)2]·10CH3OH·11H2O (3), were also obtained. The carbonate ions in 1–3 were formed by spontaneous fixation of atmospheric CO2. Structural analysis revealed that the metallic core in 1 can be viewed as a Ni2Dy2 butterfly connecting two NiDy subunits on each side. To our knowledge, the structural topologies of 1–3 were not reported previously. The magnetic susceptibilities of 3 were fitted by PHI, indicating that the magnetic coupling between Ni1 and Ni1a in the "Ni2Y2 butterfly" subunit of 3 is ferromagnetic. Alternating-current (ac) susceptibility studies revealed that 1–2 exhibit single molecule magnet behavior under a zero dc field. [ABSTRACT FROM AUTHOR]