Jianfeng Wu

A Linear 3d–4f Tetranuclear CoIII2DyIII2 Single-Molecule Magnet: Synthesis, Structure, and Magnetic Properties

A linear tetranuclear 3d-4f Co(2) Dy(2) cluster assembled from a polydentate Schiff base exhibits single-molecule magnet (SMM) behavior with an anisotropic barrier of 33.8 K. Due to the presence of diamagnetic cobalt(III) ions, the tetranuclear cluster of 1 behaves magnetically like a dinuclear Dy(2) system. However, the diamagnetic segment might efficiently minimize undesirable intermolecular magnetic interactions, thereby improving the performance of the SMM behavior of 1. This discrete complex presents us with a unique opportunity to study the magnetic properties and to probe the dynamics of magnetization in a magnetically isolated Dy(2) system.

Macroscopic Hexagonal Tubes of 3 d–4 f Metallocycles

The self-assembly of three giant hexagonal 3d-4f metallocycles with inner diameters of 16.4, 16.5, and 16.4 Å, is described. Hexagonal metallocycles were stacked along the crystallographic c axis, producing unique hexagonal macroscopic tubular single crystals. The assembly mechanism of the tubular crystals was investigated. Remarkably, all three hexagonal metallocycles show typical single-molecule magnet behavior, benefiting from the ferromagnetic couplings between the 3d and 4f ions.

Enhancement of Magnetocaloric Effect through Fixation of Carbon Dioxide: Molecular Assembly from Ln4 to Ln4 Cluster Pairs

A series 1.Ln of tetranuclear lanthanide clusters [Ln4(μ4-O)L2(PhCOO)6]·solvent (Ln = Gd (1.Gd), Dy (1.Dy), Ho (1.Ho)) and octanuclear lanthanide Ln4 cluster pairs 2.Ln [Ln8(μ3-OH)4(CO3)2L4(PhCOO)8]·solvent (Ln = Gd (2.Gd), Dy (2.Dy), Tb (2.Tb)) were assembled by using a bi-Schiff-based ligand H2L and characterized structurally and magnetically. Interestingly, the octanuclear Ln4 cluster pairs 2.Ln are proposed to be assembled from the tetranuclear clusters 1.Ln through the uptake of CO2 from air in a more basic media. X-ray structural analyses approved the possible evolution mechanism. Magnetic studies reveal the coexistence of ferro- and anti-ferromagnetic interaction in 1.Gd and 2.Gd by simulating the direct-current magnetic susceptibility and indicate the CO32- bridges produce weak ferromagnetic interaction in 2.Gd rather than anti-ferromagnetic interaction by benzoate bridges in 1.Gd. The magnitude of the magnetocaloric effect has been examined and shows that complex 2.Gd exhibits larger magnetocaloric effect than 1.Gd, which could be probably ascribed to the weak ferromagnetic interaction produced by the CO32- bridges.

Axial Ligand Field in D4d Coordination Symmetry: Magnetic Relaxation of Dy SMMs Perturbed by Counteranions

A series of mononuclear DyIII complexes with the general formula [DyLz2(salicylaldehyde)2]·X·solvent (Lz = 6-pyridin-2-yl[1,3,5]triazine-2,4-diamine; X = OH- (1·OH), Cl- (2·Cl), Br- (3·Br)) have been synthesized using mixed salicylaldehyde/pyridinyl-triazine ligands and discriminative counteranions. The DyIII ion in these three complexes resides in a similar D4d coordination geometry with counteranions perturbing the coordination environment and bond lengths and angles in the lattice. Magnetostructural studies reveal that the asymmetric distribution of salicylaldehyde/pyridinyl-triazine ligands and the presence of discriminative counteranions result in the coexistence of large anisotropy and quantum tunneling of magnetization. The magnetic anisotropy is dominated by the axial ligand field with short Dy-Osali distances and large ∠Osali-Dy-Osali angles, while the quantum tunneling relaxation is probably dictated by the π-π stacking of the Lz ligands, which induces an axial constriction of the coordinating plane. Ab initio calculations substantiate the diversity of the magnetic behaviors in these complexes and highlight the importance of axial ligand field with short Dy-Osali distances, large ∠Osali-Dy-Osali angles and less ligand stacking in these pseudo-D4d-symmetrical single-molecule magnets.

Manipulating the Relaxation of Quasi-D4d Dysprosium Compounds through Alternation of the O-Donor Ligands

Three mononuclear DyIII complexes with the same auxiliary ligand Lz (2,4-diamino-6-pyridyl-1,3,5-triazine), [Dy(TTA)3Lz] (1Dy) (TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate), [Dy(acac)3Lz]·CH3OH·0.5H2O (2Dy) (acac = acetylacetonate), and [Dy(MQ)2Lz2]Br·CH3OH (3Dy) (HMQ = 2-methyl-8-quinolinol), have been synthesized through alteration of the ligands containing O donors. In all three complexes, the DyIII ions are eight-coordinate and submitted to pseudo- D4 d symmetry in the first coordination sphere. It is noteworthy that the TTA ligands in 1Dy are easily substituted by other bidentate capping ligands with O donors, leading to distinct magnetic properties, which were studied experimentally and via ab initio calculations. All three complexes were found to exhibit single-molecule magnet behavior with Ueff of 22 cm-1 (1Dy), 112 cm-1 (2Dy), and 56 cm-1 (3Dy) under zero applied dc field. Complex 1Dy demonstrates inferior SIM properties compared with 2Dy and 3Dy, which can be attributed to the strong electron-withdrawing effects of TTA ligands, as confirmed by theoretical calculations. However, butterfly-shaped magnetic hysteresis in 1Dy and 3Dy was observed at 1.9 K, while not in 2Dy.

Two 1,8-naphthalenediol-based dysprosium complexes: syntheses, structures, and magnetic properties

Abstract Two mononuclear dysprosium complexes, [Dy(H2L1)2(CH3OH)2]Cl∙6CH3OH (1) and [Dy(H3L2)2(CH3OH)2]Cl∙2H2O (2), derived from 1,8-naphthalenediol-based ligands were synthesized and characterized by single-crystal X-ray diffraction and magnetic measurements. Single-crystal X-ray analyses reveal that the eight-coordinate DyIII ion exhibits distorted triangular dodecahedron geometry in both complexes. The mononuclear units in 2 are further connected into one-dimensional chains via hydrogen-bond interactions. Alternating-current magnetic susceptibility studies indicate that 2 shows slow relaxation of the magnetization with a roughly estimated activation energy of 3 K and pre-exponential factor of 10−6 s, while 1 does not show any ac signals.