Three CoII complexes, [Co2(H2L1)2](ClO4)4·4CH3OH (1), [Co2(H4L2)2](ClO4)4 (2) and [Co4(H4L2)4](ClO4)8 (3), were constructed by self-assembly of symmetrical dihydrazone ligands H2L1 and H4L2 with CoII ions under different synthetic conditions. Fish-bone like...
Solvent effects on the structures and magnetic properties
of single-molecule
magnets (SMMs) have been of great interest for modification of the
SMMs using chemical modulation. By systematically varying the reaction
solvents (MeOH, ethanol, n-propanol, and n-butanol), we have successfully synthesized a series of
DyIII-H4daps complexes (H4daps = N′,N‴-[(1E,1′E)-pyridine-2,6-diylbis(ethan-1-yl-1-ylidene)]bis(2-hydroxybenzohydrazide),
including two binuclear compounds, [Dy2(H2daps)2(MeOH)4(H2O)2](CF3SO3)2·0.5MeOH (1
MeOH
) and [Dy2(H2daps)3(EtOH)2]·2EtOH·Et2O (2
EtOH
), and two mononuclear compounds, [Dy(H4daps)2](CF3SO3)3·n-PrOH (3
PrOH
) and [Dy(H4daps)(CF3SO3)3(n-BuOH)]·0.5Et2O (4
BuOH
). Using different solvents,
the ligand-to-metal ratios can be adjusted from 1:1 in 1
MeOH
and 4
BuOH
to 3:2 in 2
EtOH
and 2:1
in 3
PrOH
. Through the solvent
crossover experiments, the role of the solvents and the conditions
to form these complexes were carefully studied. The size of the different
alcohols, their coordination ability to the DyIII center,
and the solubility of the complexes in these alcohols might affect
the assembly process and lead to modification of the structures and
magnetic properties of these DyIII-H4daps complexes.
Magnetic studies revealed that these four complexes all exhibit slow
magnetic relaxation under a zero or an applied direct-current field,
with an energy barrier of about 100 K for the binuclear compound 1
MeOH
. In combination with theoretical
calculations, the magnetic–structure relationship of these
four compounds has been analyzed. This work demonstrates the crucial
role of different solvent molecules in the fine-tuning of the structures
and magnetic performances of different lanthanide complexes.
Photosensitive lanthanide‐based single‐molecule magnets (Ln−SMM) are very attractive for their potential applications in information storage, switching, and sensors. However, the light‐driven structural transformation in Ln−SMMs hardly changes the coordination number of the lanthanide ion. Herein, for the first time it is reported that X‐ray (λ=0.71073 Å) irradiation can break the coordination bond of Dy−OH2 in the three‐dimensional (3D) metal‐organic framework Dy2(amp2H2)3(H2O)6 ⋅ 4H2O (MDAF‐5), in which the {Dy2(OPO)2} dimers are cross‐linked by dianthracene‐phosphonate ligands. The structural transformation proceeds in a single‐crystal‐to‐single‐crystal (SC‐SC) fashion, forming the new phase Dy2(amp2H2)3(H2O)4 ⋅ 4H2O (MDAF‐5‐X). The phase transition is accompanied by a significant change in magnetic properties due to the alteration in coordination geometry of the DyIII ion from a distorted pentagonal bipyramid in MDAF‐5 to a distorted octahedron in MDAF‐5‐X.
Using a novel tricompartmental hydrazone ligand, a set of trinuclear Dy3 complexes has been isolated and structurally characterized. Complexes Dy3 ⋅ Cl, Dy3 ⋅ Br, and Dy3 ⋅ ClO4 feature a similar overall topology but different anions (Cl−, Br−, or ClO4−) in combination with exogenous OH− and solvent co‐ligands, which is found to translate into very different magnetic properties. Complex Dy3 ⋅ Cl shows a double relaxation process with fast quantum tunneling of the magnetization, probably related to the structural disorder of μ2‐OH− and μ2‐Cl− co‐ligands. Relaxation of the magnetization is slowed down for Dy3 ⋅ Br and Dy3 ⋅ ClO4, which do not show any structural disorder. In particular, fast quantum tunneling is suppressed in case of Dy3 ⋅ ClO4, resulting in an energy barrier of 341 K and magnetic hysteresis up to 3.5 K; this makes Dy3 ⋅ ClO4 one of the most robust air‐stable trinuclear SMMs. Magneto‐structural relationships of the three complexes are analyzed and rationalized with the help of CASSCF/RASSI‐SO calculations.
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