Ligand Modulation of the Structures and Magnetic Relaxation in Triangular Dy3 Complexes Based on a Tricompartmental Scaffold.

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.

X-Ray Triggered Coordination-Bond Breakage in Dysprosium-Organic Framework and its Impact on Magnetic Properties.

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 (amp2 H2 )3 (H2 O)6 ⋅ 4H2 O (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 (amp2 H2 )3 (H2 O)4 ⋅ 4H2 O (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.

Solvent Modification of the Structures and Magnetic Properties of a Series of Dysprosium(III) Single-Molecule Magnets.

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 (1MeOH) and [Dy2(H2daps)3(EtOH)2]·2EtOH·Et2O (2EtOH), and two mononuclear compounds, [Dy(H4daps)2](CF3SO3)3·n-PrOH (3PrOH) and [Dy(H4daps)(CF3SO3)3(n-BuOH)]·0.5Et2O (4BuOH). Using different solvents, the ligand-to-metal ratios can be adjusted from 1:1 in 1MeOH and 4BuOH to 3:2 in 2EtOH and 2:1 in 3PrOH. 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 1MeOH. 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.

Self-assembly of fish-bone and grid-like CoII-based single-molecule magnets using dihydrazone ligands with NNN and NNO pockets.

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 the self-assembly of the symmetrical dihydrazone ligands H2L1 and H4L2 with CoII ions under different synthetic conditions. The fish-bone-like complex 1 was obtained using the ligand H2L1 in methanol via the solvothermal method, while the self-assembly of H4L2 with CoII ions is solvent-dependent, producing the fish-bone-like complex 2 and [2 × 2] grid-like complex 3. Magnetic susceptibility measurements and theoretical calculations reveal that the large negative D values for the three complexes stem from their easy-axis magnetic anisotropy. Ac magnetic susceptibility measurements disclosed field-induced slow magnetic relaxation behaviors and the presence of Raman and/or direct processes of the three complexes at various applied dc fields.

Terminal-fluoride-coordinated air-stable chiral dysprosium single-molecule magnets.

Terminal fluoride ligands generate strong magnetic anisotropy in air-stable chiral dysprosium enantiomers supported by a bulky equatorial macrocycle, exhibiting a typical zero-field single-molecule magnet behaviour.