Developing a “Highway Code” To Steer the Structural and Electronic Properties of FeIII/DyIII Coordination Clusters

Single-molecule magnet behavior in heterometallic decanuclear [Ln2Fe8] (Ln = Y, Dy, Ho, Tb, Gd) coordination clusters

Five decanuclear lanthanide-iron clusters, formulated as [Ln2Fe8(hmp)10(μ2-OH)4(μ3-OH)2(μ4-O)4(H2O)6]·6ClO4·xH2O (x ≈ 8, Ln = Y for 1; x ≈ 6, Ln = Dy for 2; x ≈ 6, Ln = Ho for 3; x ≈ 7, Ln = Tb for 4; x ≈ 7, Ln = Gd for 5, Hhmp = 2-(hydroxymethyl)pyridine), have been synthesized and structurally characterized. Single-crystal structural analysis reveals that the cluster consists of six face-sharing defective cubane units. Dynamic magnetic investigations indicated that cluster 2 exhibits single-molecule magnet behavior under a zero dc field eliciting an effective energy barrier of Ueff = 17.76 K and a pre-exponential factor of τ0 = 7.93 × 10-8 s. Investigation of the performance of a series of FeIII-DyIII SMMs indicates that the relatively low energy barrier in 2 is associated with the weak ferromagnetic coupling between FeIII and DyIII ions, while the strength of ferromagnetic interaction in these clusters is mainly related to the bond distances between DyIII and O atoms coordinated to FeIII ions. Clusters 3 and 4 exhibit similar dual relaxation pathways under their respective optimal external applied dc field, where the direct relaxation process occurs in the low-frequency area, which impedes the extraction of the Ueff, while the secondary relaxation process appears at a higher frequency, which is probably a connection with intermolecularly driven relaxation. Our findings offer a magneto-structural correlation model for further investigating the single-molecule magnet behavior in lanthanide-iron systems.

Heterometallic clusters based on an uncommon asymmetric "V-shaped" [Fe3+(μ-OR)Ln3+(μ-OR)2Fe3+]6+ (Ln = Gd, Tb, Dy, Ho) structural core and the investigation of the slow relaxation of the magnetization behaviour of the [Fe2Dy] analogue

The synthesis, crystal structures, Mössbauer spectra and variable temperature dc and ac magnetic susceptibility studies of a new family of trinuclear heterometallic Fe³⁺/Ln³⁺ complexes, [Fe₂Ln(PhCO₂)₃((py)₂CO₂)((py)₂C(OMe)O)₂(NO₃)Cl] (Ln = Gd (1/Gd), Tb (1/Tb), Dy (1/Dy), and Ho (1/Ho)), where (py)₂CO₂^2- and (py)₂C(OMe)O^- are the anions of the gem-diol and hemiketal derivatives of di-2-pyridyl ketone, are reported. Compounds 1/Ln are based on an asymmetric "V-shaped" [Fe³⁺(μ-OR)Ln(μ-OR)₂Fe³⁺]⁶⁺ structural core formed from the connection of the two terminal Fe³⁺ centers to the central Ln³⁺ ion either through one or two alkoxide groups originating from the alkoxide-type bridging ligands. Direct current magnetic susceptibility studies reveal the presence of weak antiferromagnetic interactions between the Fe³⁺ ions. Alternating current magnetic studies indicate the presence of a slow-magnetic relaxation process in 1/Dy with an energy barrier U_eff = 6.7 (±0.3) K and a pre-exponential factor, τ₀ = 2.2 (±0.4) × 10^-7 s. The electronic, magnetic and relaxation properties of the complexes were further monitored by variable temperature ⁵⁷Fe Mössbauer spectroscopy. At T > 80 K the spectra from the complexes comprise two quadrupole doublets the hyperfine parameters of which reflect the distinct coordination environment of the two Fe³⁺ terminal sites. At T < 20 K, the Mössbauer spectra for 1/Dy are affected by magnetic relaxation effects. At 1.5 K, the spectrum of 1/Dy comprises well defined magnetic sextets indicating relaxation times slower than the characteristic time of the Mössbauer technique (10^-7 s) in agreement with the dynamic magnetic measurements. 1/Gd exhibits broad unresolved magnetic sextets at 1.5 K indicating that the spin relaxation time is of the order of the Mössbauer characteristic time at this temperature. For 1/Tb, 1/Ho the Mössbauer spectra exhibit slight broadening even at the lowest available temperature consistent with magnetic relaxation times less than 10^-7 s.

{ScnGdn} Heterometallic Rings: Tunable Ring Topology for Spin-Wave Excitations

Data carriers using spin waves in spintronic and magnonic logic devices offer operation at low power consumption and free of Joule heating yet requiring noncollinear spin structures of small sizes. Heterometallic rings can provide such an opportunity due to the controlled spin-wave transmission within such a confined space. Here, we present a series of {Sc_nGd_n} (n = 4, 6, 8) heterometallic rings, which are the first Sc-Ln clusters to date, with tunable magnetic interactions for spin-wave excitations. By means of time- and temperature-dependent spin dynamics simulations, we are able to predict distinct spin-wave excitations at finite temperatures for Sc₄Gd₄, Sc₆Gd₆, and Sc₈Gd₈. Such a new model is previously unexploited, especially due to the interplay of antiferromagnetic exchange, dipole-dipole interaction, and ring topology at low temperatures, rendering the importance of the latter to spin-wave excitations.

Recent advances in lanthanide coordination polymers and clusters with magnetocaloric effect or single-molecule magnet behavior

Molecular magnetorefrigerant materials for low-temperature magnetic refrigeration and single-molecule magnets for high-density information storage and quantum computing have received extensive attention from chemists and magnetic experts. Lanthanide ions with unique magnetic properties have always been considered as ideal candidates for the construction of such materials. This frontier article focuses on Gd^III-based molecular magnetorefrigerants and lanthanide-based single-molecule magnets and highlights the most significant advances.

Carboxylate-Decorated Aggregation of Octanuclear Co4Ln4 (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties

One-pot reactions of an asymmetric carboxy-ether-phenol based Schiff base H₂L (2-((2-hydroxy-3-methoxybenzylidene)amino)benzoic acid) with selected Ln(NO₃)₃·nH₂O and [Co₂(μ-OH₂)(O₂CCMe₃)₄(HO₂CCMe₃)₄] (Co₂-Piv) in basic MeOH medium resulted in a family of three octanuclear complexes, [Co^II₄Ln^III₄L₄(μ_1,3-Piv)₄(μ_1,1,3-Piv)₂(η¹-Piv)₂(μ₃-OH)₄(MeOH)₂]·mMeOH·nH₂O (Ln = Dy; m = 3, n = 1 (1), Ho; m = 4, n = 0 (2), Yb; m = 3, n = 1 (3)). The coordination aggregates thus obtained were nicely sustained by four ligand anions and eight externally added carboxylate anions showing three different modes of intermetallic connectivity. The options for incorporating different 4f ions in an investigative synthesis, without altering the resulting intermetallic core structure, were successful for the three representative examples. Single-crystal X-ray diffraction studies revealed that the compounds are isostructural and built from two initially formed partial dicubane-type Co₂Ln₂L₂ units. In each of the tetranuclear parts, the metal ion centers are held together by two L^2-, two μ₃-HO^-, three Piv^- bridges, one terminal Piv^-, and one terminal MeOH. Four carboxylate ends of four L^2- units are responsible for connecting two Co₂Ln₂ units into octanuclear structures. The unique distortion around the Co^II centers is achieved from the facile coordination of bigger 4f ions to the adjacent hard OO sites. The distortion is further maintained by the presence of terminal COO^- groups from L^2-. The dc magnetic susceptibility data revealed ferromagnetic coupling between the Co^II and Ln^III centers within the series, whereas the ac magnetic susceptibility measurements identified only 1, having a highly anisotropic Dy^III ion, as a single-molecule magnet in the absence of any external magnetic field, with an energy barrier U_eff of 12.5 K.

Exploring the Role of Intramolecular Interactions in the Suppression of Quantum Tunneling of the Magnetization in a 3d-4f Single-Molecule Magnet

Hydroxide-bridged Fe^III₄Ln^III₂ clusters having the general formula [Fe₄Ln₂(μ₃-OH)₂(mdea)₆(SCN)₂(NO₃)₂(H₂O)₂]·4H₂O·2MeCN {Ln = Y (1), Dy (2), mdea = N-methyldiethanolamine} were synthesized and magnetically characterized. The thermal relaxation of the magnetization for 2 and the diluted Fe^III₄Dy^IIIY^III complex 3 (with and without applied field) has been analyzed. The diluted sample shows a dominant QTM at low temperatures that can be removed with a 0.15 T dc field. Both 2 and 3 show moderately high U_eff barriers and exhibit hysteresis loops until 5 K.

The Influence of Halide Substituents on the Structural and Magnetic Properties of Fe6Dy3 Rings

We report the synthesis and magnetic properties of three new nine-membered Fe(III)-Dy(III) cyclic coordination clusters (CCCs), with a core motif of [Fe₆Dy₃(μ-OMe)₉(vanox)₆(X-benz)₆] where the benzoate ligands are substituted in the para-position with X = F (1), Cl (2), Br (3). Single crystal X-ray diffraction structure analyses show that for the smaller fluorine or chlorine substituents the resulting structures exhibit an isostructural Fe₆Dy₃ core, whilst the 4-bromobenzoate ligand leads to structural distortions which affect the dynamic magnetic behavior. The magnetic susceptibility and magnetization of 1-3 were investigated and show similar behavior in the dc (direct current) magnetic data. Additional ac (alternating current) magnetic measurements show that all compounds exhibit frequency-dependent and temperature-dependent signals in the in-phase and out-of-phase component of the susceptibility and can therefore be described as field-induced SMMs. The fluoro-substituted benzoate cluster 1 shows a magnetic behavior closely similar to that of the corresponding unsubstituted Fe₆Dy₃ cluster, with U_eff = 21.3 K within the Orbach process. By increasing the size of the substituent toward 4-chlorobenzoate within 2, an increase of the energy barrier to U_eff = 36.1 K was observed. While the energy barrier becomes higher from 1 to 2, highlighting that the introduction of different substituents on the benzoate ligand in the para-position has an impact on the magnetic properties, cluster 3 shows a significantly different SMM behavior where U_eff is reduced in the Orbach regime to only 4.9 K.

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.

Effect of ligand substitution on the SMM properties of three isostructural families of double-cubane Mn4Ln2 coordination clusters

Three isostructural Mn–Ln families consists of 22 complexes have been presented. Only 7, 15, and 22 for Tb, 8 and 16 for Dy, and 20 for Sm displayed slow magnetization relaxation.

Synthesis, structures and magnetic properties of linear {CoII2LnIII2} coordination clusters

A series of linear CoII2LnIII2 coordination clusters have been synthesized and their magnetic properties have been systematically studied.

Systematic studies of hexanuclear {MIII4LnIII2} complexes (M = Fe, Ga; Ln = Er, Ho): structures, magnetic properties and SMM behavior

The first heterometallic Ga^III–Er^III single-molecule magnet has been synthesized and the role of Ga^III in extracting the Fe^III–Er^III and Er^III–Er^III interaction has been assessed.

First heterometallic GaIII–DyIII single-molecule magnets: implication of GaIII in extracting Fe–Dy interaction

First heterometallic Ga^III–Dy^III single-molecule magnets have been synthesized and the role of the Ga^III in extracting Fe^III–Dy^III interaction has been assessed.

A single molecule magnet to single molecule magnet transformation via a solvothermal process: Fe4Dy2 → Fe6Dy3

Under ambient and solvothermal conditions four new compounds [FeIII4LnIII2(μ₃-OH)₂(mdea)₄(m-NO₂C₆H₄COO)₈]·3MeCN and [FeIII6LnIII3(μ₄-O)₃(μ₃-O)(mdea)₅(m-NO₂C₆H₄COO)₉]·3MeCN (Ln = Y and Dy) have been synthesised and their magnetic properties investigated.