Influence of the Different Types of Auxiliary Noncarboxylate Organic Ligands on the Topologies and Magnetic Relaxation Behavior of Zn-Dy Heterometallic Single Molecule Magnets

In this work, we first synthesized a Zn-Dy complex, [Zn₆Dy₂(L)₆(tea)₂(CH₃OH)₂]·6CH₃OH·8H₂O (H₂L = N-3-methoxysalicylidene-2-amino-3-hydroxypyridine, teaH₃ = triethanolamine, 1), by employing H₂L, anhydrous ZnCl₂, and Dy(NO₃)₃·5H₂O reacting with auxiliary ligand teaH₃ in the mixture of CH₃OH and DMF. When teaH₃ and the solvent CH₃OH in the reaction system of 1 were replaced by the auxiliary ligand 2,6-pyridinedimethanol (pdmH₂) and the solvent MeCN, another Zn-Dy complex, [Zn₄Dy₄(L)₆(pdm)₂(pdmH)₄]·10CH₃CN·5H₂O (2), was obtained. For 1, its crystal structure can be viewed as a dimer of two Zn₃Dy^III units. However, for 2, four Dy^III form a zigzag arrangement, and each of its terminals linked two Zn^II ions. Interestingly, although the structural topologies of 1 and 2 are different, the coordination geometries of Dy^III in 1 and 2 are all triangular dodecahedron (TDD-8). The difference is that the continuous shape measure (CShM) values of Dy^III in 1 are larger than the corresponding values in 2. Magnetic investigation revealed that the diluted sample 1@Y exhibits two magnetic relaxation processes, while 2 only exhibits a single relaxation process. Ab initio calculations indicated that, in the crystal lattice of 1, two complexes exhibiting slightly different CShM values of Dy^III result in the double relaxation behavior of 1@Y. However, for 2, one of two Dy^III fragments possesses a fast quantum tunneling of magnetization (QTM), resulting in its magnetic process presented at T < 1.8 K, so 2 exhibits single relaxation behavior. More importantly, the theoretical calculations also clearly indicated that the weak ligation at equatorial sites of Dy^III in 1 and 2 ensure 1@Y and 2 possess SMM behavior, although the coordination geometry of Dy^III (TDD-8) in 1 and 2 severely deviates from the ideal polyhedron and its axial symmetry is low.

Study on the Magneto-Structural Correlation of a New Dinuclear Cobalt(II) Complex with Double μ-Phenoxo Bridges

A new μ-phenoxo-bridged dinuclear cobalt(II) complex, [Co₂(L)₂(acac)₂(H₂O)] (1), has been synthesized by employing a new ligand, (4-methyl-2-formyl-6-(((2-trifluoromethyl)phenyl)methyliminomethyl) phenol) (HL). Structural analysis of complex 1 reveals that the geometry around cobalt centers is best described as a distorted octahedron and the distance of cobalt neighbors is 3.128(0) Å. The magnetic property studies indicate that complex 1 exhibits strong spin-orbit coupling effects and weak ferromagnetic coupling between two high-spin Co(II) centers linked by double μ-O_phenoxo bridges, with J = 1.87(2) cm^-1. The studies show that not only the Co-O-Co angle affects the alignment of the cobalt spins but also the dihedral angle between the CoOCo plane and the phenyl plane plays an important role in the magnetic coupling in this [Co₂O₂] system. Thus, the small bridging angles (96.96(11) and 96.91(11)°) and the large dihedral angles between the CoOCo plane and the phenyl plane (63.0(1) and 30.6(1)°) induce intramolecular ferromagnetic exchange interaction in complex 1.

Modulating the structural topologies and magnetic relaxation behaviour of the Mn–Dy compounds by using different auxiliary organic ligands

A MnIII4Dy^III complex and a one-dimensional chain containing MnIII2Dy^III units have been obtained by using different combinations of organic ligands, and a slow magnetic relaxation behavior was observed for both complexes.

Assembly of chiral 3d–4f wheel-like cluster complexes with achiral ligands: single-molecule magnetic behavior and magnetocaloric effect

With the help of perchlorate ions, chiral M₃Ln₃ wheel-like cluster complexes were constructed from achiral ligands, and showed single-molecule magnetic behavior and magnetocaloric effect.

Synthesis, crystal structures and magnetic properties of a series of chair-like heterometallic [Fe4Ln2] (Ln = GdIII, DyIII, HoIII, and ErIII) complexes with mixed organic ligands

Four chair-like hexanuclear Fe-Ln complexes containing mixed organic ligands, namely, [Fe₄Ln₂{(py)₂CO₂}₄(pdm)₂(NO₃)₂(H₂O)₂Cl₄]·xCH₃CN·yH₂O (Ln = Gd^III (1, x = 1, y = 0), Dy^III (2, x = 1, y = 1), Ho^III (3, x = 0, y = 2), and Er^III (4, x = 1, y = 3); (py)₂CO₂H₂ = the gem-diol form of di-2-pyridyl ketone and pdmH₂ = 2,6-pyridinedimethanol) have been obtained by employing di-2-pyridyl ketone and 2,6-pyridinedimethanol reacting with FeCl₃ and Ln(NO₃)₃ in MeCN. The structures of 1-4 are similar to each other except for the number of lattice solvent molecules. Four Fe^III and two Ln^III in these complexes comprise a chair-like core with the "body" constructed by four Fe^III ions and the "end" constructed by two Ln^III ions. Among the four compounds, 2 shows field-induced single molecule magnet behavior as revealed by ac magnetic susceptibility studies, with the effective energy barrier and the pre-exponential factor of 22.07 K and 8.44 × 10^-7 s, respectively. Ab initio calculations indicated that, among 2_Dy, 3_Ho and 4_Er fragments, the energy gap between the lowest two spin-orbit states for 2_Dy is the largest, while the tunneling gap for 2 is the smallest. These might be the reasons for complex 2 exhibiting SMM behavior. Additionally, the orientations of the magnetic anisotropy of Dy^III in 2 were obtained by electrostatic calculations and ab initio calculations, both indicating that the directions of the main magnetic axis of Dy1 ions are almost aligned along Dy1-O5 (O5 from the pdm^2- ligand).

Modulation of the directions of the anisotropic axes of DyIII ions through utilizing two kinds of organic ligands or replacing DyIII ions by FeIII ions

Two complexes based on Dy₄ or Fe₂Dy₂ tetrahedral unit have been obtained by employing mixed organic ligands. The directions of the easy magnetization for the Dy^III in both complexes were successfully modulated.