Approaching the 1000 K energy barrier in high coordinate lanthanide single-ion magnets: Increasing Ueff in the [Dy(Tp2-py)F]+ moiety with tetrahydrofuran

Using the existing architecture of [Dy(Tp2-py)F]+ that supports a terminal Dy-F bond, the synthesis and isolation of [Dy(Tp2-py)F(THF)2](PF6) and its diamagnetic yttrium analogue have been achieved. Alternating current magnetic susceptibility studies show an increased effective energy barrier of Ueff = 661(6) cm-1 (951(8) K), the highest yet reported for a high coordinate (n > 8) lanthanide single-ion magnet.

Stepwise and Controllable Synthesis of Mesoporous Heterotrimetallic Catalysts Based on Predesigned Al4 Ln4 Metallocycles

The motivation for making heterometallic compounds stemmed from their emergent synergistic properties and enhanced capabilities for applications. However, the atomically precisely controlled synthesis of heterometallic compounds remains a daunting challenge of the complications that arise when applying several metals and linkers. Herein, a stepwise and controlled method is reported for the accurate addition of second and third metals to homometallic aluminum macrocycles based on the synergistic coordination and hard-soft acid-base theory. These heterometallic compounds showed a good Lewis acid catalytic effect, and the addition of hetero-metals significantly improved the catalytic effect and rate, among that the conversion rate of compound AlOC-133 reached 99.9% within half an hour. This method combines both the independent controllability of stepwise assembly with the universality of one-step methods. Based on the large family of clusters, the establishment of this method paves the way for the controllable and customized molecular-level synthesis of heterometallic materials and creates materials customized for preferential application.

{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.

Synthesis and structures of fluoride-bridged dysprosium clusters: influence of fluoride ions on magnetic relaxation behaviors

The synthesis of fluoride-bridged 1Dy, 2Dy and hepta-nuclear 3Dy dysprosium complexes is reported here and a hydroxy-bridged dinuclear dysprosium complex 4Dy is synthesized for comparison.

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.

Synthesis and Characterisation of Luminescent [CrIII 2 L(μ-carboxylato)]3+ Complexes with High-Spin S=3 Ground States (L=N6 S2 donor ligand)

The synthesis, structure, magnetic, and photophysical properties of two dinuclear, luminescent, mixed-ligand [CrIII 2 L(O2 CR)]3+ complexes (R=CH3 (1), Ph (2)) of a 24-membered binucleating hexa-aza-dithiophenolate macrocycle (L)2- are presented. X-ray crystallographic analysis reveals an edge-sharing bioctahedral N3 Cr(μ-SR)2 (μ1,3 -O2 CR)CrN3 core structure with μ1,3 -bridging carboxylate groups. A ferromagnetic superexchange interaction between the electron spins of the Cr3+ ions leads to a high-spin (S=3) ground state. The coupling constants (J=+24.2(1) cm-1 (1), +34.8(4) cm-1 (2), H=-2JS1 S2 ) are significantly larger than in related bis-μ-alkoxido-μ-carboxylato structures. DFT calculations performed on both complexes reproduce both the sign and strength of the exchange interactions found experimentally. Frozen methanol-dichloromethane 1 : 1 solutions of 1 and 2 luminesce at 750 nm when excited into the 4 LMCT state on the 4 A2 → 2 T1 (ν2 ) bands (λexc =405 nm). The absolute quantum yields (ΦL ) for 1 and 2 were found to be strongly temperature dependent. At 77 K in frozen MeOH/CH2 Cl2 glasses, ΦL =0.44±0.02  (for 1), ΦL =0.45±0.02  (for 2).

A simple methodology for constructing ferromagnetically coupled Cr(iii) compounds

A large family of chromium(iii) dimers has been synthesised and magneto-structurally characterised using a combination of carboxylate and diethanolamine type ligands. The compounds have the general formula [Cr2(R1-deaH)2(O2CR2)Cl2]Cl where R1 = Me and R2 = H (1), Me (2), CMe3 (3), Ph (4), 3,5-(Cl)2Ph (5), (Me)5Ph (6), R1 = Et and R2 = H (7), Ph (8). The compound [Cr2(Me-deaH)2Cl4] (9) was synthesised in order to study the effect of removing/adding the carboxylate bridge on the observed magnetic behaviour. Direct current (DC) magnetic susceptibility measurements showed ferromagnetic (FM) exchange interactions between the Cr(iii) centres in the carboxylate bridged family with coupling constants in the range +0.37 < J < +8.02 cm-1. Removal of the carboxylate to produce the dialkoxide-bridged compound 9 resulted in antiferromagnetic (AFM) exchange between the Cr(iii) ions. DFT calculations reveal the ferromagnetic exchange is the result of an orbital counter-complementarity effect occuring upon introduction of the bridging carboxylate.

Arraying Octahedral {Cr2Dy4} Units into 3D Single-Molecule-Magnet-Like Inorganic Compounds with Sulfate Bridges

Two novel 3D pure inorganic compounds based on [Cr₂Dy₄(μ₄-O)₂(μ₃-OH)₄]¹⁰⁺ cluster units and sulfate anions are presented. Both complexes exhibit single-molecule-magnet (SMM)-like behavior. Permutation of the magnetic moment direction among SMM-like cluster units has a significant effect on the performance of molecular nanomagnets, and directional consistency shows obvious advantages.

Targeted replacement: systematic studies of dodecanuclear {MLn} coordination clusters (M = Cr, Co; Ln = Dy, Y)

Three dodecanuclear 3d-4f coordination clusters, [CrIII6LnIII6(μ3-OH)8(tbdea)6(C6H5COO)16]·2H2O (Ln = Dy (1), Y (2)) and [CoIII6DyIII6(μ3-OH)8(nbdea)6(m-CH3C6H4COO)16]·2H2O·2CH3CN (3), have been synthesized under solvothermal conditions and characterized. Single-crystal X-ray diffraction analysis revealed that all three compounds possess an analogous {MIII6LnIII6} core (M = Cr, Co; Ln = Dy, Y) and dc magnetic susceptibility studies indicated that the magnetic exchange couplings between DyIII ions are dominant antiferromagnetic, while the CrIII-DyIII interactions are weakly ferromagnetic. Furthermore, the ac magnetic susceptibility measurements showed that both CrIII6DyIII6 compound 1 and CoIIi6DyIII6 compound 3 containing highly anisotropic DyIII ions displayed single-molecule magnetic (SMM) behavior with the energy barrier Ueff increasing from 12.8 K (for 1) to 20.8 K (for 3), indicating that weak 3d-4f exchange couplings enhance the QTM and reduce the energy barrier.

Magnetic Nature of the CrIII-LnIII Interactions in [CrIII2LnIII3] Clusters with Slow Magnetic Relaxation

Two 3d-4f hetero-metal pentanuclear complexes with the formula {[CrIII2LnIII3L10(OH)6(H2O)2]Et3NH} [Ln=Tb (1), Dy (2); HL=pivalic acid, Et3N=triethylamine] have been produced. The metal core of each cluster is made up of a trigonal bipyramid with three LnIII ions (plane) and two CrIII ions (above and below) held together by six μ3-OH bridges. Also reported with this series is the diamagnetic CrIII-YIII analogue (3). Fortunately, we successfully prepared AlIII-LnIII analogues with the formula {[AlIII2LnIII3L10(OH)6(H2O)2]Et3NH⋅H2O} [Ln=Tb (4), Dy (5)], containing diamagnetic AlIII ions, which can be used to evaluate the CrIII-LnIII magnetic nature through a diamagnetic substitution method. Subsequently, static (dc) magnetic susceptibility studies reveal dominant ferromagnetic interactions between CrIII and LnIII ions. Dynamic (ac) magnetic susceptibility studies show frequency-dependent out-of-phase (χ'') signals for [CrIII2TbIII3] (1), [CrIII2DyIII3] (2), and [AlIII2DyIII3] (5), which are derived from the single-ion behavior of LnIII ions and/or the CrIII-LnIII ferromagnetic interactions.

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.

Quenching the Quantum Tunneling of Magnetization in Heterometallic Octanuclear {TMIII4 DyIII4 } (TM=Co and Cr) Single-Molecule Magnets by Modification of the Bridging Ligands and Enhancing the Magnetic Exchange Coupling

We report the synthesis, structural characterisation, magnetic properties and provide an ab initio analysis of the magnetic behaviour of two new heterometallic octanuclear coordination complexes containing Co^III and Dy^III ions. Single-crystal X-ray diffraction studies revealed molecular formulae of [Co^III₄ Dy^III₄ (μ-OH)₄ (μ₃ -OMe)₄ {O₂ CC(CH₃ )₃ }₄ (tea)₄ (H₂ O)₄ ]⋅4 H₂ O (1) and [Co^III₄ Dy^III₄ (μ-F)₄ (μ₃ -OH)₄ (o-tol)₈ (mdea)₄ ]⋅ 3 H₂ O⋅EtOH⋅MeOH (2; tea^3- =triply deprotonated triethanolamine; mdea^2- =doubly deprotonated N-methyldiethanolamine; o-tol=o-toluate), and both complexes display an identical metallic core topology. Furthermore, the theoretical, magnetic and SMM properties of the isostructural complex, [Cr^III₄ Dy^III₄ (μ-F₄ )(μ₃ -OMe)_1.25 (μ₃ -OH)_2.75 (O₂ CPh)₈ (mdea)₄ ] (3), are discussed and compared with a structurally similar complex, [Cr^III₄ Dy^III₄ (μ₃ -OH)₄ (μ-N₃ )₄ (mdea)₄ (O₂ CC(CH₃ )₃ )₄ ] (4). DC and AC magnetic susceptibility data revealed single-molecule magnet (SMM) behaviour for 1-4. Each complex displays dynamic behaviour, highlighting the effect of ligand and transition metal ion replacement on SMM properties. Complexes 2, 3 and 4 exhibited slow magnetic relaxation with barrier heights (U_eff ) of 39.0, 55.0 and 10.4 cm^-1 respectively. Complex 1, conversely, did not exhibit slow relaxation of magnetisation above 2 K. To probe the variance in the observed U_eff  values, calculations by using CASSCF, RASSI-SO and POLY_ANISO routine were performed on these complexes to estimate the nature of the magnetic coupling and elucidate the mechanism of magnetic relaxation. Calculations gave values of J_Dy-Dy as -1.6, 1.6 and 2.8 cm^-1 for complexes 1, 2 and 3, respectively, whereas the J_Dy-Cr interaction was estimated to be -1.8 cm^-1 for complex 3. The developed mechanism for magnetic relaxation revealed that replacement of the hydroxide ion by fluoride quenched the quantum tunnelling of magnetisation (QTM) significantly, and led to improved SMM properties for complex 2 compared with 1. However, the tunnelling of magnetisation at low-lying excited states was still operational for 2, which led to low-temperature QTM relaxation. Replacement of the diamagnetic Co^III ions with paramagnetic Cr^III led to Cr^III ⋅⋅⋅Dy^III coupling, which resulted in quenching of QTM at low temperatures for complexes 3 and 4. The best example was found if both Cr^III and fluoride were present, as seen for complex 3, for which both factors additively quenched QTM and led to the observation of highly coercive magnetic hysteresis loops above 2 K. Herein, we propose a synthetic strategy to quench the QTM effects in lanthanide-based SMMs. Our strategy differs from existing methods, in which parameters such as magnetic coupling are difficult to control, and it is likely to have implications beyond the Dy^III SMMs studied herein.

Synthesis, structural characterization and magnetic behaviour of a family of [CoIII2LnIII2] butterfly compounds

We report a family of butterfly-like [CoIII2LnIII2] complexes with Ln = Gd, Tb, Dy, Ho, Er and Yb. All of them are isostructural but the complex with Ln = Gd strings in a one dimensional chain. The Dy member shows slow relaxation of magnetization under zero DC applied field, while all the others only after a small DC field is applied.

Lanthanide dinuclear complexes constructed from mixed oxygen-donor ligands: the effect of substituent positions of the neutral ligand on the magnetic dynamics in Dy analogues

Two series of lanthanide dinuclear complexes with the general formulae, [Ln(n-PNO)(Bza)3(H2O)] {Bza = benzoic acid; n = 3, n-PNO = 3-picoline N-oxide, Dy(1) and Er(2); and n = 4, n-PNO = 4-picoline N-oxide, Nd(3), Eu(4), Gd(5), Tb(6), Dy(7), Er(8) and Y(9)} have been successfully synthesized by the hydrothermal method. Single-crystal X-ray diffraction experiments illustrate that the two series of compounds possess similar carboxylic ligand-bridged dinuclear structure and coordination geometry around the lanthanide ions despite the different methyl-substituent positions on the neutral ligand. Comparative studies of the Dy analogues in the static-field measurements reveal only a little difference with a small butterfly-shaped opening for complex 1 and a close hysteresis loop for 7 at 2.0 K. However, systematic investigations of the alternating-current (ac) measurements indicate that the different substituent positions of the picoline N-oxide ligand have a significant effect on the magnetic relaxation dynamics. A more substantial suppression of the quantum tunnelling of magnetization (QTM) effect and pronounced slow magnetic relaxation were observed in complex 7 as compared to 1 under both zero and a 1 kOe static field.

Supramolecular 3d–4f single-molecule magnet architectures

Cooperative hydrogen bonds are key to the formation of nanosized {[{Ln^III}{H₂O⊂CrIII3LnIII6}]₂(H₂O)}-type single-molecule magnets, templated by a central water triad.

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.

Synthesis, structure, magnetic and magnetocaloric properties of a series of {CrIII4LnIII} complexes

Magnetic properties and magnetocaloric effect of rare heterometallic Cr(iii)–Ln(iii) complexes are reported.

Single molecule magnet behaviour in a rare trinuclear {CrIIIDyIII2} methoxo-bridged complex

A new neutral hetero-trinuclear {Cr^III–DyIII2} coordination complex exhibiting single molecule magnet behaviour has been synthesized.