Hui-Sheng Wang

To precisely regulate Orbach and Raman processes in polynuclear complexes, four novel Co2IIILnIII complexes with the molecular formula of [Co2IIILn(HL)2{(py)2CO2}(OAc)3]·2CH3CN·1.5H2O (Ln = Tb (1Tb), Dy (2Dy), and Ho (3Ho); (py)2CO2H2 = the gem-diol form of di-2-pyridyl ketone(dpk); OAc– = acetate) and [Co2IIIDy(HL)2{(py)2CO2}(OAc)2(NO3)]·2CH3OH·H2O (4Dy) have been obtained. The main difference between 1Tb–3Ho and 4Dy is that one μ1-κ1-O,O′-OAc– ligand coordinates with LnIII in 1Tb, 2Dy, and 3Ho, while one μ1-κ1-O,O′-NO3– coordinates with DyIII in 4Dy. Alternating current (ac) susceptibility studies revealed that 1Tb and 3Ho show field-induced slow magnetic relaxation signatures, while 2Dy and 4Dy both exhibit field-induced single-molecule magnet behavior. Additionally, the Raman/Orbach ratios are about 18 for 2Dy and about 5480 for 4Dy, indicating that the relative weighting of the Raman and the Orbach relaxation channels can be markedly modulated by OAc–/NO3– substitution. Ab initio calculations analyzed the difference in the magnetic relaxation behavior of 2Dy and 4Dy and revealed that the directions of the main magnetic axes of DyIII are sensitive to the coordinated OAc–/NO3– ions, namely, the main magnetic axis of DyIII in 2Dy is almost parallel to the Dy1–O2 bond, while the axis of DyIII in 4Dy deviates from all Dy–O bond directions.

In this review, the synthetic strategies, magnetic properties and magnetic relaxation mechanism of the Dy ^III -containing single-ion magnets or single-molecule magnets have been discussed from an electrostatic perspective.

We reported a novel “Y”-shaped Mn^III₅Dy₃ complex with SMM behavior, and found that the U_cal value of individual Dy^III is the highest when the electrostatic potentials from two sides of its equatorial plane are completely equivalent to each other.

A novel Ni₄Dy₄ complex constructed using two kinds of organic ligands has been obtained. The complex and its diluted compound both exhibit single molecule magnet behavior under a zero dc field.

A star-like CoIII2DyIII2 complex (1) and a cross-shaped Co ^II/III –Dy complex (2) have been obtained, in which 1 exhibits double magnetic relaxation behavior, while 2 only shows slow magnetic relaxation signals.

In this work, we employed an asymmetric auxiliary organic ligand (1,1,1-trifluoroacetylacetone, Htfac) to further regulate the magnetic relaxation behavior of series of Dy₂ single-molecule magnets (SMMs) with a N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H₂L) ligand. Fortunately, an air-stable Dy₂ complex, [Dy₂(L)₂(tfac)₂] (1; Htfac = 1,1,1-trifluoroacetylacetone) was obtained at room temperature. A structural analysis indicated that some Dy–O or Dy–N bond lengths for 1 are not in the range of those for the complexes [Dy^III₂(L)₂(acac)₂]·2CH₂Cl₂ (Dy₂-acac; Hacac = acetylacetone) and [Dy^III₂(L)₂(hfac)₂] (Dy₂-hfac; Hhfac = hexafluoroacetylacetone), although the electron-withdrawing ability of tfac^– is stronger than that of acac^– but weaker than that of hfac^–. Additionally, the Dy–O3/O3a (the two O atoms bridged to Dy^III ions) bond lengths are also affected by the asymmetrical Htfc ligand. This indicated that the charge distribution of the coordination atoms around Dy^III has been modified in 1, which leads to the fine-tuning of the magnetic relaxation behavior of 1. Magnetic studies indicated that the values of effective energy barrier (U_eff) for 1 and its diluted sample (2) are 234.8(3) and 188.0(6) K, respectively, which are both higher than the reported value of 110 K for the complex Dy₂-hfac. More interestingly, 1 exhibits a magnetic hysteresis opening when T < 2.5 K at zero field, while the hysteresis loops of 2 are closed at a zero dc field. This discrepancy is due to the weak intramolecular exchange coupling in 2, which cannot overcome the QTM of the single Dy^III ion. Ab initio calculations for 1 revealed that the charge distributions of the coordination atoms around Dy^III ions were regulated and the intramolecular exchange coupling was indeed improved when the asymmetrical Htfc was employed as a ligand for the synthesis of this kind of Dy₂ SMM.

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 [email protected] 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 [email protected] . 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 [email protected] 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.

A DyNa complex ( 1 ) and a DyNa ₂ 1D chain ( 2 ) have been obtained; their square antiprism coordination geometries were changed from the bicapped triangular prism of the reported DyNa ₂ complex. Compounds 1 and 2 exhibit single ion magnet behavior.