Synthesis, structures and magnetic studies of hexanuclear lanthanide complexes: SMM behavior of the DyIII analogue and MCE properties of the GdIII analogue

The synthesis, structure and magnetic properties of homometallic hexanuclear lanthanide complexes [Ln6(HL)4(tfa)4(S)2]·2NO3·x H2O·yMeOH (1, Ln = Gd, S = MeOH, x = 0, y = 0; 2, Ln = Tb, S = H2O, x = 2, y = 2; 3, Ln = Dy, S = MeOH, x = 0, y = 2; 4, Ln = Er, S = MeOH, x = 0, y = 2). [(H4L) = 6-((bis(2-hydroxyethyl)amino)-N'-(2-hydroxybenzylidene)picolinohydrazide) (tfa = trifloroacetylacetone)] are reported. These hexanuclear assemblies are made up of two trinuclear triangular sub-units linked through the oxygen atoms of two phenoxide bridging groups in a corner sharing arrangement. Magnetic studies reveal that 1 displays a magnetocaloric effect with a maximum value of -ΔSm = 21.03 J kg-1 K-1 at T = 3 K and under an applied field change ΔB = 5 T. Complex 3 shows slow relaxation of magnetization even under zero applied field although a clear maximum in the ac susceptibility plots cannot be seen. However, under an optimal applied field of 0.2 T, clear maxima are observed in the out-of-phase (χ''M) component of the ac susceptibility in the temperature range 3.5 K (2 kHz) to 10.5 K (10 kHz). The temperature dependence of the relaxation times could be fitted to the sum of Orbach, Raman and QTM relaxation processes affording the following parameters: τo = 3.4(9) × 10-8 s, Ueff = 94(2) K, BRaman = 16.43(1) K-n s-1, n = 3.2(3) and τQTM = 0.0044(3) s. 4, under an applied magnetic field of 0.2 T, shows slow relaxation of magnetization through a thermally activated Orbach process with Ueff = 18.2(9) K and τo = 3.5(3) × 10-8 s.

Magnetic cooling: a molecular perspective

The magnetocaloriceffect is considered as an energy-efficient and environmentally friendly technique which can take cooling technology to the next level. Apart from its commercial application at room temperature, magnetic refrigeration is an up-and-coming solution for the cryogenic regime, especially as an alternative to He³ systems. Molecular magnets reveal advantageous features for ultra-low cooling which are competitive with intermetallic and lanthanide alloys. Here, we present a guide to the current status of magnetocaloric effect research of molecular magnets with a theoretical background focused on the inverse magnetocaloric effect and an overview of recent results and developments, including the rotating magnetocaloric effect.

The first exploration of coordination chemistry using a methyl substituted o-vanillin based ligand: an example starting with Dy4/Zn2Dy2 systems displaying slow relaxation of magnetization

Two butterfly-shaped Dy4 and Zn2Dy2 complexes displaying slow relaxation of magnetization have been synthesized from a new methyl substituted o-vanillin based ligand, enlarging the scope for finding better SMMs.

Synthesis, structural characterization, and magnetic property study of {Cr3Ln3}, Ln = Gd and Dy complexes

We have successfully prepared and structurally characterized triangle-in-triangle {Cr₃Ln₃} complexes with Ln = Gd and Dy employing alcohol-amine, N-methyldiethanolamine (H₂mdea) and pivalate ligands. These complexes and the Yttrium analogue proved to be isostructural and crystallized in a P₁ triclinic cell. DC and AC magnetic measurements were carried out and supported by quantum computations at DFT and CASSCF levels. DC magnetic data are dominated by the Cr(III)-Ln(III) antiferromagnetic interaction and by single-ion anisotropy in the case of the Dy(III) complex. Ln(III)-Ln(III) magnetic interactions are negligible, as well as Cr(III)-Cr(III) ones. From AC data, slow relaxation of the magnetization is observed at 0 DC applied magnetic field in the case of the Dy(III) complex below 4 K. From temperature and field dependence data, possible Raman and Orbach relaxation mechanisms are established in the absence of quantum tunnelling pathways, suggesting a successful suppression of the latter due to the Cr(III)-Dy(III) exchange interaction.

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.

Strong intramolecular DyIII–DyIII magnetic couplings up to 15.00 cm−1 in phenoxyl-bridged dinuclear 4f complexes

Unexpectedly, intramoleular Dy^III–Dy^III magnetic couplings are up to 15.00 cm⁻¹ in the phenolate-bridged Dy₂ complexes. And single-molecule magnet behavior is exhibited with effective energy of 76.18 K under zero dc field.

Zn2Ln2 complexes with carbonate bridges formed by the fixation of carbon dioxide in the atmosphere: single-molecule magnet behaviour and magnetocaloric effect

In the self-assembly process, CO₂ in the air is automatically fixed to Zn₂Ln₂ cluster molecular materials.

Modulation of the properties of dinuclear lanthanide complexes through utilizing different β-diketonate co-ligands: near-infrared luminescence and magnetization dynamics

Four Dy₂ complexes based on the ligand H₂L display various slow magnetic relaxation behaviors through utilizing different β-diketonate co-ligands.

Near-infrared luminescence and magnetic properties of dinuclear rare earth complexes modulated by β-diketone co-ligands

The magnetic properties of complexes based on a Schiff base ligand H₂L can be modulated by subtle changes in the coordination environment resulting from changes in the co-ligand substituents.

Structural and cryogenic magnetic properties of RE2Ni2In (RE = Pr, Nd, Dy and Ho) compounds

The crystal structures, magnetic properties and magneto-caloric effects (MCEs) of RE₂Ni₂In (RE = Pr, Nd, Dy and Ho) compounds were investigated. The results indicate that Pr₂Ni₂In and Nd₂Ni₂In compounds have a tetragonal Mo₂FeB₂-type structure belonging to the P4/mbm space group and undergo a second-order paramagnetic to ferromagnetic (PM to FM) transition at a Curie temperature (T_C) of 7.5 and 10.5 K, respectively, whereas Dy₂Ni₂In and Ho₂Ni₂In compounds have an orthorhombic Mn₂AlB₂-type structure belonging to the space group Cmmm and possess a magnetic transition from PM to antiferromagnetic (AFM) at a Néel temperature T_N of 19 and 10.5 K together with a first-order field induced metamagnetic transition, respectively. Moreover, an additional magnetic transition at a lower temperature of around 5.5 K is detected for the Ho₂Ni₂In compound. A considerable reversible magneto-caloric effect is observed accompanying the magnetic phase transition, and the maximum values of the magnetic entropy change (-ΔS) of the present RE₂Ni₂In series compounds are determined to be 9.3, 11.5, 6.4 and 11.5 J kg^-1 K^-1 with a magnetic field change (ΔH) of up to 0-5 T for RE = Pr, Nd, Dy and Ho, respectively.

Syntheses, crystal structures and magnetic properties of a series of ZnII2LnIII2 compounds (Ln = Gd, Tb, Dy, Ho and Er): contrasting structural and magnetic features

In the five ZnII2LnIII2 compounds – (i) the Tb^III and Er^III analogues show slow relaxation of the magnetization, while the Ho^III system and, surprisingly, the Dy^III analogue don’t; (ii) the Gd^III system shows the MCE; and (iii) interestingly, the Ln–O bond length increases with the increase of atomic number.

Enhanced energy barriers triggered by magnetic anisotropy modulation via tuning the functional groups on the bridging ligands in Dy2 single-molecule magnets

Two dinuclear dysprosium complexes of 1 and 2 have been synthesized and both of them exhibit SMM behavior. The energy barrier is enhanced ca. 35 K by elaborately tuning the backbones of the ligands.

Cooperative effects of metal cations and coordination modes on luminescent s-block metal–organic complexes constructed from V-shaped 4,4′-sulfonyldiphenol

Thirteen s-block metal–organic complexes with different supramolecular networks arising from the coordination modes of the ligands and properties of the metal cations have been synthesized and exhibit violet and blue luminescence in the solid state at room temperature.