Modulating magnetic anisotropy in linear tetranuclear dysprosium(III) complexes via coordinated anions

We report the synthesis, structures, and magnetic properties of two novel linear tetranuclear complexes with the general formula [Dy4(Hheb)2(heb)4X2(MeOH)4] (X- = NO3-, OAc-; H2heb = (E)-N'-(1-(2-hydroxyphenyl)ethylidene)benzohydrazide, OAc- = acetate). The rigid ligands (Hheb-/heb2-) incorporate phenoxide groups and bridge the Dy3+ ions in an unusual tetranuclear linear assembly. Notably, we demonstrate through magnetic measurements and theoretical calculations how the anion (X) coordinated at the peripheral Dy3+ centers acts as a switch, significantly changing the magnetic anisotropy of the entire complex. This control over magnetic anisotropy through the selection of the coordinated anion offers a promising avenue for tailoring the functionality of single-molecule magnets.

Effect of Substituents in Equatorial Hexaazamacrocyclic Schiff Base Ligands on the Construction and Magnetism of Pseudo D6h Single-Ion Magnets

Three mononuclear DyIII compounds [DyL1(Ph3SiO)2][BPh4]·MeCN·2H2O (1), [DyL2(Ph3SiO)2][BPh4]·C2H5OH·H2O (2), and [DyL3(Ph3SiO)(OAc)][BPh4]·CH3OH·3H2O (3) and their corresponding YIII diluted analogues [Dy0.0967Y0.9033L1(Ph3SiO)2][BPh4]·MeCN·2H2O (1@Y), [Dy0.2668Y0.7332L2(Ph3SiO)2][BPh4]·C2H5OH·H2O (2@Y), and [Dy0.1260Y0.8740L3(Ph3SiO)(OAc)][BPh4]·CH3OH·3H2O (3@Y) were synthesized with hexaazamacrocyclic Schiff base ligands as an equatorial ligand. The substituents in the equatorial hexaazamacrocyclic Schiff base ligand show a significant effect on the replacement of the axial ligands. Compounds 1, 2, and 3 are typical zero dc field single-molecule magnets with effective energy barriers (Ueff) of 1092(6), 946.1(7), and 150.1(9) K, respectively. Although the effective energy barriers of 1 and 2 are close, the magnetic hysteresis remains open up to 20 K for 1, twice as large as that of 2 (10 K), which is different from the previously reported compounds, probably due to nonplanarity N6 in the equator. Ab initio calculations indicate that the ground states of compounds 1 and 2 exhibit high anisotropy and pure second and third excited states, while compound 3 exhibits pure ground-state anisotropy and highly mixed excited states, leading to the easy occurrence of quantum tunneling of magnetization between the ground and excited states in compound 3. This work indicates that the substituents in equatorial hexaazamacrocyclic Schiff base ligands have a significant effect on the construction and magnetic properties of DyIII SIMs with D6h symmetry.

A highly anisotropic family of hexagonal bipyramidal Dy(III) unsaturated 18-crown-6 complexes exceeding the blockade barrier over 2700 K: a computational exploration

In the present work, we have explored a series of unsaturated hexa-18-crown-6 (U18C6) ligands towards designing highly anisotropic Dy(III) based single-ion magnets (SIMs) with the general formula [Dy(U18C6)X2]+ (where U18C6 = [C12H12O6] (1), [C12H12S6] (2), [C12H12Se6] (3), [C12H12O4S2] (4), [C12H12O4Se2] (5) and X = F, Cl, Br, I, OtBu and OSiPh3). By analysing the electronic structure, bonding and magnetic properties, we find that the U18C6 ligands prefer stabilising the highly symmetric eight-coordinated hexagonal bipyramidal geometry (HBPY-8), which is the source of the near-Ising type anisotropy in all the [Dy(U18C6)X2]+ complexes. Moreover, the ability of sulfur/selenium substituted U18C6 ligands to stabilize the highly anisotropic HBPY-8 geometry makes them more promising towards engineering the equatorial ligand field compared to substituted saturated 18C6 ligands where the exodentate arrangement of the S lone pairs results in low symmetry. Magnetic relaxation analysis predicts a record barrier height over 2700 K for [Dy(C12H12O6)F2]+ and [Dy(C12H12S6)X2]+ (where X = F, OtBu and OSiPh3) complexes, nearly 23% higher than those of the top performing Dy(III) based SIMs in the literature.

Contrasting impact of coordination polyhedra and site symmetry on the electronic energy levels in nine-coordinated Eu(III) and Sm(III) crystals structures determined from single crystal luminescence spectra

Lanthanide luminescence is characterised by "forbidden" 4f-4f transitions and a complicated electronic structure. Our understanding of trivalent lanthanide(III) ion luminescence is centered on Eu3+ because absorbing and emitting transitions in Eu3+ occur from a single electronic energy level. In Sm3+ both absorbing and emitting multiplets have a larger multiplicity. A band arising in transitions from the first emitting state multiplet to the ground state multiplet will have nine lines for a Sm3+ complex. In this study, high-resolution emission and excitation spectra were used to determine the electronic energy levels for the lowest multiplet and first emitting multiplet in four Sm3+ compounds with either tricapped trigonal prismatic TTP or capped square antiprismatic cSAP coordination polyhedra but different site symmetry. This was achieved by the use of Boltzmann distribution population analysis and experimentally determined transition probabilities from emission and excitation spectra. Using this analysis it was possible to show the effect of changing three oxygen atoms with three nitrogen atoms in the donor set for two compounds with the same coordination polyhedra and site symmetry. This work celebrates the 40th anniversary of Kirby and Richardson's first report of [Eu(ODA)3]3- luminescence.

Luminescent Single-Molecule Magnets as Dual Magneto-Optical Molecular Thermometers

Luminescent thermometry allows the remote detection of the temperature and holds great potential in future technological applications in which conventional systems could not operate. Complementary approaches to measuring the temperature aiming to enhance the thermal sensitivity would however represent a decisive step forward. For the first time, we demonstrate the proof-of-concept that luminescence thermometry could be associated with a complementary temperature readout related to a different property. Namely, we propose to take advantage of the temperature dependence of both magnetic (canonical susceptibility and relaxation time) and luminescence features (emission intensity) found in Single-Molecule Magnets (SMM) to develop original dual magneto-optical molecular thermometers to conciliate high-performance SMM and Boltzmann-type luminescence thermometry. We highlight this integrative approach to concurrent luminescent and magnetic thermometry using an air-stable benchmark SMM [Dy(bbpen)Cl] (H2 bbpen=N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl)ethyl-enediamine)) exhibiting Dy3+ luminescence. The synergy between multiparametric magneto-optical readouts and multiple linear regression makes possible a 10-fold improvement in the relative thermal sensitivity of the thermometer over the whole temperature range, compared with the values obtained with the single optical or magnetic devices.

Regulating Magnetic Relaxations of Cyano-Bridged {DyIII MoV } Systems by Tuning the N-Sites in β-Diketone Ligands

Cyano-bridged 4d-4f molecular nanomagnets have re-called increasing research interests in molecular magnetism since they offer more possibilities in achieving novel nanomagnets with versatile structures and magnetic interactions. In this work, four β-diketone ligands bearing different substitution N-sites were designed and synthesized, namely 1-(2-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL1 ), 1,3-Bis (3-pyridyl)-1,3-propanedione (HL2 ), 1-(4-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL3 ), and 1,3-Bis (4-pyridyl)-1,3-propanedione (HL4 ), to tune the magnetic relaxation behaviors of cyano-bridged {DyIII MoV } systems. By reacting with DyCl3  ⋅ 6H2 O and K4 Mo(CN)8  ⋅ 2H2 O, four cyano-bridged complexes, namely {[Dy[MoV (CN)8 ](HL1 )2 (H2 O)3 ]} ⋅ 6H2 O (1), {[Dy[MoV (CN)8 ](HL2 )(H2 O)3 (CH3 OH)]}2  ⋅ 2CH3 OH ⋅ 3H2 O (2), {[Dy[MoV (CN)8 ](HL3 )(H2 O)2 (CH3 OH)] ⋅ H2 O}n (3), and {[Dy[MoV (CN)8 ](HL4 )2 (H2 O)3 ]} ⋅ 2H2 O⋅CH3 OH (4) were obtained. Structural analyses revealed that 1 and 4 are binuclear complexes, 2 has a tetragonal structure, and 3 exhibits a stair-like polymer chain structure. The DyIII ions in all complexes have eight-coordinated configurations with the coordination spheres DyO7 N1 for 1 and 4, DyO6 N2 for 2, and DyO5 N3 for 3. Magnetic measurements indicate that 1 is a zero-field single-molecule magnet (SMM) and complexes 2-4 are field-induced SMMs, with complex 4 featuring a two-step relaxation process. The magnetic characterizations and ab initio calculations revealed that changing the N-sites in the β-diketone ligands can effectively alter the structures and magnetic properties of cyano-bridged 4d-4f nanomagnets by adjusting the coordination environments of the DyIII centers.

Structure and Magnetic Properties of Homoleptic Trivalent Tris(alkyl)lanthanides

Six new solvent-free, homoleptic paramagnetic tris(alkyl)lanthanides Ln{C(SiHMe₂)₃}₃ (1Ln) and Ln{C(SiHMe₂)₂Ph}₃ (2Ln) (Ln = Gd, Dy, and Er) were synthesized to investigate the magnetic properties of 4f organometallic compounds stabilized by secondary Ln↼H-Si and benzylic interactions. The unit cell of 1Gd contains one independent molecule (Z = 2), while 1Dy and 1Er crystallize with four independent isostructural molecules per unit cell (Z = 16). In all molecules, as in other 1Ln compounds, the three tris(dimethylsilyl)methyl ligands form a trigonal planar LnC₃ core, and six secondary interactions involving Ln↼H-Si bonding in Ln{C(SiHMe₂)₃}₃ form above and below the equatorial plane. Two and five crystallographically independent molecules of each 2Ln (2Gd, Z = 8; 2Dy, Z = 20) form with three π-coordinated phenyl groups in addition to either one or two secondary Ln↼H-Si interactions per molecule. The packing of these midseries organolanthanide compounds contrasts the single crystallographically unique molecules in previously reported La{C(SiHMe₂)₃}₃ (1La, Z = 2, Z' = 1) and La{C(SiHMe₂)₂Ph}₃ (2La, Z = 2, Z' = 1/3). 2La doped with 2Dy can adopt the crystallographic structure of 2La, which promotes magnetic properties, namely a higher χ_mT value at low temperatures as well as stronger magnetic anisotropy. The ac susceptibility data for 10% 2Dy doped into 2La suggests slow relaxation at low temperatures with a relaxation barrier of ∼45 K. The computed saturated magnetization of 1Er (M ≈ 4.5 μ_B) and 1Dy (M ≈ 6 μ_B) matches the experimental values, while the computed value for 2Dy better matches the value measured for 2Dy diluted in 2La (M ≈ 5 μ_B). Gas-phase calculations predict that the ground-state and first excited-state multiplet separations are larger for 1Er than 2Er, while the ordering for dysprosium is 1Dy > 2Dy.

Ab initio prediction of key parameters and magneto-structural correlation of tetracoordinated lanthanide single-ion magnets

Single-molecule magnets (SMMs) have great potential in becoming revolutionary materials for micro-electronic devices. As one type of SMM and holding the performance record, lanthanide single-ion magnets (Ln-SIMs) stand at the forefront of the family. Lowering the coordination number (CN) is an important strategy to improve the performance of Ln-SIMs. Here, we report a theoretical study on a typical group of low-CN Ln-SIMs, i.e., tetracoordinated structures. Our results are consistent with those of experiments and they identify the same three best Ln-SIMs via a concise criterion, i.e., the co-existence of long τ_QTM and high U_eff. Compared to the record-holding dysprosocenium systems, the best SIMs here possess τ_QTM values that are shorter by several orders of magnitude and U_eff values that are lower by ∼1000 Kelvin (K). These are important reasons for the fact that the tetracoordinated Ln-SIMs are clearly inferior to dysprosocenium. A simple but intuitive crystal-field analysis leads to several routes to improve the performance of a given Ln-SIM, including compression of the axial bond length, widening the axial bond angle, elongation of the equatorial bond length and usage of weaker equatorial donor ligands. Although these routes are not brand-new, the most efficient option and the degree of improvement resulting from it are not known in advance. Consequently, a theoretical magneto-structural study, covering various routes, is carried out for the best Ln-SIM here and the most efficient route is shown to be widening the axial ∠O-Dy-O angle. The most optimistic case, having a ∠O-Dy-O of 180°, could have a τ_QTM (up to 10³ s) and U_eff (∼2400 K) close to those of the record-holders. Subsequently, a blocking temperature (T_B) of 64 K is predicted to be possible for it. A more practical case, with ∠O-Dy-O being 160°, could have a τ_QTM of up to 400 s, U_eff of around 2200 K and the possibility of a T_B of 57 K. Although having an inherent precision limit, these predictions provide a guide to performance improvement, starting from an existing system.

[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight

Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW₉O₃₃]^9- based lanthanide-containing polyoxometalates [Cs_xK_36-x{Ln₆(H₂O)₁₂(α-AsW₉O₃₃)₆}]·yH₂O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln₃(H₂O)₆(α-AsW₉O₃₃)₃]^18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H₂O)₂(α-AsW₉O₃₃)]^6- as a building unit. In all the complexes, [α-AsW₉O₃₃]^9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW₉O₃₃]^9- unit bridges two Ln(III) centers through four μ₂-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of m_J states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.

Structure and bonding patterns in heterometallic organometallics with linear Ln-Pd-Ln motifs

Complexes with short intermetallic distances between transition metal fragments and lanthanide (Ln) fragments are fascinating objects of study, owing to the ambiguity of the nature of the interaction. The addition of the divalent lanthanide fragments Cp*₂Ln(OEt₂) (Ln = Sm or Yb) to a Pd(ii) complex bearing the deprotonated form of the redox-active, non-symmetrical ligand, 2-pyrimidin-2-yl-1H-benzimidazole (Hbimpm), leads to two isostructural complexes, of the general formula (Cp*₂Ln)₂[μ-Pd(pyridyl)₂] (Ln = Sm (4) and Yb (5)). These adducts have interesting features, such as unique linear Ln-Pd-Ln arrangements and short Ln-Pd distances, which deviate from the expected lanthanide contraction. A mixed computational and spectroscopic study into the formation of these adducts gathers important clues as to their formation. At the same time, thorough characterization of these complexes establishes the +3 oxidation state of all the involved Ln centers. Detailed theoretical computations demonstrate that the apparent deviation from lanthanide contraction is not due to any difference in the intermetallic interaction between the Pd and the Ln, but that the fragments are joined together by electrostatic interactions and dispersive forces. This conclusion contrasts with the findings about a third complex, Cp*₂Yb(μ-Me)₂PdCp* (6), formed during the reaction, which also possesses a short Yb-Pd distance. Studies at the CASSCF level of theory on this complex show several orbitals containing significant interactions between the 4f and 4d manifolds of the metals. This demonstrates the need for methodical and careful analyses in gauging the intermetallic interaction and the inadequacy of empirical metrics in describing such phenomena.

Evidence of symmetry breaking in a Gd2 di-nuclear molecular polymer

A chiral 3D coordination compound, [Gd₂(L)₂(ox)₂(H₂O)₂], arranged around a dinuclear Gd unit has been characterized by X-ray photoemission and X-ray absorption measurements in the context of density functional theory studies. Core level photoemission of the Gd 5p multiplet splittings indicates that spin orbit coupling dominates over j-J coupling evident in the 5p core level spectra of Gd metal. Indications of spin-orbit coupling are consistent with the absence of inversion symmetry due to the ligand field. Density functional theory predicts antiferromagnet alignment of the Gd₂ dimers and a band gap of the compound consistent with optical absorption.

Magnetic and optical studies of a new family of multidimensional and multiproperty PO-lanthanide(III) derived systems

A new family of lanthanide compounds has been synthesized using 1,2-bis(diphenylphosphino)ethane dioxide (dppeO₂) as an O-donor ligand through the phosphoryl group to lanthanide(III) cations and structurally, magnetically and optically studied. Depending on the lanthanide, two different topologies appear: the two-dimensional structure [Ln^III(dppeO₂)_1.5(NO₃)₃(H₂O)_0.5]_n (Ln = Ce (1), Sm (2) and Dy (6)) and the one-dimensional structure [Ln(dppeO₂)(NO₃)₃DMF]_n (Ln = Eu (3), Gd (4) and Tb (5)). Some of the Ln-derived complexes have been used as structural probes, while others have been synthesized to use the specific characteristics of each cation to take advantage of their magnetic/luminescence properties. Complex 6 presents slow relaxation of the magnetization while 2, 3 and 5 present emitting properties in the visible range.

Theoretical Investigation of Single-Molecule-Magnet Behavior in Mononuclear Dysprosium and Californium Complexes

Early-actinide-based (U, Np, and Pu) single-molecule magnets (SMMs) have yet to show magnetic properties similar to those of highly anisotropic lanthanide-based ones. However, there are not many studies exploring the late-actinides (more than half-filled f shells) as potential candidates for SMM applications. We computationally explored the electronic structure and magnetic properties of a hypothetical Cf(III) complex isostructural to the experimentally synthesized Dy(dbm)₃(bpy) complex (bpy = 2,2'-bipyridine; dbm = dibenzoylmethanoate) via multireference methods and compared them to those of the Dy(III) analogue. This study shows that the Cf(III) complex can behave as a SMM and has a greater magnetic susceptibility compared to other experimentally and computationally studied early-actinide-based (U, Np, and Pu) magnetic complexes. However, Cf spontaneously undergoes α-decay and converts to Cm. Thus, we also explored the isostructural Cm(III)-based complex. The computed magnetic susceptibility and g-tensor values show that the Cm(III) complex has poor SMM behavior in comparison to both the Dy(III) and Cf(III) complexes, suggesting that the performance of Cf(III)-based magnets may be affected by α-decay and can explain the poor performance of experimentally studied Cf(III)-based molecular magnets in the literature. Further, this study suggests that the ligand field is dominant in Cf(III), which helps to increase the magnetization blocking barrier by nearly 3 times that of its 4f congener.

3D-Frameworks and 2D-networks of lanthanide coordination polymers with 3-pyridylpyrazole: photophysical and magnetic properties

A series of 15 lanthanide-containing coordination polymers, both 3D- and 2D-networks, as well as complexes of Ln-trichlorides with 3-(3-pyridyl)pyrazole (3-PyPzH), were synthesized. A large structural diversity is observed depending on the ligand content: 3∞[Ln(3-PyPzH)Cl₃], Ln = Eu and Gd, of sra topology, 2∞[Sm(3-PyPzH)Cl₃], 2∞[Ln₂(3-PyPzH)₃Cl₆]·2solv, Ln = Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺ and Er³⁺, solv = Tol and MeCN, of sql topology and 2∞[Ln(3-PyPzH₂)Cl₄], Ln = La and Nd, of hcb topology with salt like complexes of the formula [(3-PyPzH₂)][Ln(3-PyPzH)₂Cl₄], Ln = Eu, Tb, Dy and Ho. The products were characterized by single-crystal and powder X-ray diffraction, high-temperature X-ray diffraction, differential thermal analysis and thermogravimetry (DTA/TG) combined with mass spectrometry, differential scanning calorimetry (DSC), IR-spectroscopy, UV-visible spectrophotometry, photoluminescence spectroscopy, and magnetic susceptibility. Absorption spectroscopy shows ion-specific 4f-4f transitions that can be assigned to Sm³⁺, Eu³⁺, Dy³⁺, Ho³⁺ and Er³⁺ in a wide range from the UV-VIS to NIR region. An excellent antenna effect through ligand-metal energy transfer was observed in 2∞[Tb₂(3-PyPzH)₃Cl₆]·2solv, leading to high efficiency of the luminescence indicated by a quantum yield up to 76%. Direct current magnetic susceptibility studies reveal the absence of interatomic interaction for Dy³⁺ and Er³⁺ and weak ferromagnetic interaction for Ho³⁺. Thermal analysis shows good stability up to 365 °C for 2∞[Ho₂(3-PyPzH)₃Cl₆]·2MeCN.

A Tetranuclear Dysprosium Schiff Base Complex Showing Slow Relaxation of Magnetization

A tetranuclear dysprosium Schiff base complex was isolated by reacting dysprosium chloride with 2-hydroxy-3-methoxybenzaldehyde and 2-(aminomethyl)pyridine in-situ under basic conditions. The isolated Dy(III) complex was characterized by elemental analyses, single crystal X-ray diffraction and molecular spectroscopy. The complex crystallizes in the triclinic space group P-1 with unit cell parameters of a = 10.2003 (4), b = 13.8602 (5), c = 14.9542 (6), α = 94.523 (3), β = 109.362 (4), and γ = 99.861 (3). The magnetic properties of 1 have been investigated by DC and AC susceptibility measurements. The DC measurements reveal weak exchange coupling of antiferromagnetic nature. In the AC measurement, the complex shows a slow relaxation of magnetization in the absence of an external magnetic field.

The coexistence of long τQTM and high Ueff as a concise criterion for a good single-molecule magnet: a theoretical case study of square antiprism dysprosium single-ion magnets

A systematic theoretical study is performed on a group of 16 square antiprism dysprosium single-ion magnets. Based on ab initio calculations, the quantum tunneling of magnetization (QTM) time, i.e., τ_QTM, and effective barrier of magnetic reversal, U_eff, are theoretically predicted. The theoretical τ_QTM is able to identify the ones with the longest QTM time with small numerical deviations. Similar results occur with respect to U_eff too. The systems possessing the best single-molecule magnet (SMM) properties here are just the ones having both the longest τ_QTM and the highest U_eff, from either experiment or theory. Thus, our results suggest the coexistence of long τ_QTM and high U_eff to be a criterion for high-performance SMMs. Although having its own limits, this criterion is easy to be applied in a large number of systems since both τ_QTM and U_eff could be predicted by theory with satisfactory efficiency and reliability. Therefore, this concise criterion could provide screened candidates for high-performance SMMs quickly and, hence, ease the burden of further exploration aiming for a higher degree of precision. This screening is important since the further exploration could easily demand tens or even hundreds of ab initio calculations for a single SMM. A semi-quantitative crystal field (CF) analysis is performed and shown here to be capable of indicating the general trends in a more chemically intuitive way. This analysis could help to identify the most important coordinating atoms for both diagonal and non-diagonal CF components. Thus, it could give some direct clues for improving the SMM properties: reducing the distance of the axial atom to the central ion, rotating the axial atom closer to the easy axis or increasing the amount of its negative charge. Correspondingly, opposite operations on the equatorial atom could give the same result.

A mononuclear nine-coordinated Dy(iii) complex exhibiting field-induced single-ion magnetism behaviour

A new mononuclear Dy(iii) complex, with the formula [Dy(Hcpt)₃]·2H₂O (1), has been successfully prepared via self-assembly between Dy(iii) ions and 2-cyano-N′-(1-(pyridin-2-yl)amido)acetyl (Hcpt) ligand. X-ray diffraction study shows that the Dy(iii) ion is nine-coordinated by three Hcpt ligands with a tridentate chelating mode, leading to an approximately monocapped square-antiprismatic (C_4v) geometry. Magnetic data analysis demonstrates that 1 performs field-induced slow magnetic relaxation with a relaxation barrier of 97.90 K, due to the quantum tunneling effect suppressed upon a static dc field of 2000 Oe. To deeply understand the magnetic behaviors, the relaxation mechanisms and magneto-structure relationship are rationally discussed using ab initio calculations as well.

Reaction of Dy(iii) ion with tridentate acylhydrazone ligand leads to a field-induced Dy(iii) SIM, of which the magneto-structural correlation is elucidated by the magnetic and theoretical studies.

Using N-Heterocyclic Carbenes as Weak Equatorial Ligands to Design Single-Molecule Magnets: Zero-Field Slow Relaxation in Two Octahedral Dysprosium(III) Complexes

We report the synthesis, structures, and magnetic investigations of two new octahedral dysprosium complexes, based on the original N-heterocyclic carbene (NHC) tridentate bis(phenoxide) ligand, of the respective formulas mer-[DyL(THF)₂Cl] (1) and mer-[DyL(THF)₃][BPh₄] (2), where L = 1,3-bis(3,5-di-tert-butyl-2-oxidophenyl)-5,5-dimethyl-3,4,5,6-tetrahydropyrimidin-1-ium chloride and THF = tetrahydrofuran. The short Dy-O distances in the axial direction in association with the weak donor ability of the NHC moiety provide a suitable environment for slow relaxation of magnetization, overcoming the previous single-molecule magnets based on NHC ligands.

Effect on the geometry over the slow relaxation of the magnetization in a series of erbium(iii) complexes based on halogenated ligands

Erbium(iii) complexes based on halogenated ligands.

The interpretation and prediction of lanthanide single-ion magnet from ab initio electronic structure calculation: The capability and limit

Single-molecule magnet (SMM) is a fascinating system holding the potential of being revolutionary micro-electronic device in information technology. However current SMMs are still far away from real-life application due to...

The rational construction of diamond-like dysprosium–hexacyanometallate frameworks featuring dynamic magnetic behaviour

Four novel diamond-like dysprosium–hexacyanometallate frameworks featuring slow magnetic relaxation have been rationally constructed by a feasible building block strategy using hexacyanometallate to link superparamagnetic dimeric units.

Schiff Base Tetranuclear Zn2Ln2 Single-Molecule Magnets bridged by Hydroxamic acid in association with Near-Infrared Luminescence

A series of Zn-Ln heteronuclear SMMs formed by hexadentate compartment Schiff base Zn-precursor and lanthanoid ions were structurally and magnetically characterized, in which the two [Zn-Ln] moieties are bridged by...

Largely Enhancing the Blocking Energy Barrier and Temperature of a Linear Cobalt(II) Complex through the Structural Distortion: A Theoretical Exploration

Complete-active-space self-consistent field and N-electron valence second-order perturbation theory have both been employed to investigate the magnetic anisotropy of one two-coordinate cobalt(II) compound via altering the Co-C bond lengths and twist angle φ. The calculated energy barrier U_eff decreases with the decrease in the Co-C bond lengths due to the gradually increasing interaction between the 3d orbitals of Co^II and the coordination ligand field and then to the decrease in the ground orbital angular moment L of Co^II. Thus, we cannot improve U_eff simply by shortening the Co-C bond lengths. However, by rotating the twist angle φ from 60 to 0°, it is surprising to find that the energy barrier and blocking temperature can be enhanced up to 1559.1 cm^-1 and 90 K, respectively, with φ = 0°, which are prominent even among lanthanide-based single-molecule magnets.

Regulating the magnetic properties of seven-coordinated Dy(III) single-ion magnets through the effect of positional isomers on axial crystal-field

Six Dy(III) single-ion magnets (SIMs) [Dy(n-OMe-bbpen)X] were synthesized by a solvothermal reaction with three positional isomers (ortho, meta, and para) of ligands n-OMe-H₂bbpen and dysprosium halides DyX₃, (n-OMe-H₂bbpen = N,N'-bis(2-hydroxy-n-methoxybenzyl)-N,N'-bis(2-methylpyridyl)ethylenediamine; n = 3, X = Cl, 1; n = 3, X = Br, 2; n = 4, X = Cl, 3; n = 4, X = Br, 4; n = 5, X = Cl, 5; n = 5, X = Br, 6). Dynamic magnetic measurements revealed that the six complexes possess notably different effective barriers of magnetic reversal: 872.0 K (1), 1210.1 K (2), 137.9 K (3), 602.6 K (4), 907.0 K (5) and 1216.7 K (6). 6 showed the best performance as SIMs among the six Dy(III) complexes. Moreover, the magnetic hysteresis loops of 6 remained open at 21 K. The crystal structures indicate the switching of local symmetry around Dy(III) ion, aroused by the variation in intermolecular interactions and steric effects. This switch is primarily correlated with the distinction of magnetic properties. In addition, ab initio calculations confirmed that the different electrostatic potential around Dy(III) ion stemming from the electronic effect of the OMe-substituted group is another factor leading to the distinction in magnetic properties. This work warns us that when designing ligands for Dy-SIMs, the effect of positional isomerism on magnetic performance must be considered, which is one of the factors that can easily be overlooked.

Variable Luminescence and Chromaticity of Homoleptic Frameworks of the Lanthanides together with Pyridylpyrazolates

Homoleptic, 3D coordination polymers of the formula ³³ _∞ [Ln(3-PyPz)₃ ] and ³ _∞ [Ln(4-PyPz)₃ ], (3-PyPz)^- =3-(3-pyridyl)pyrazolate anion, (4-PyPz)^- =3-(4-pyridyl)pyrazolate anion, both C₈ H₆ N₃ ^- , Ln=Sm, Eu, Gd, Tb, Dy, were obtained as highly luminescent frameworks by reaction of the lanthanide metals (Ln) with the aromatic heterocyclic amine ligands 3-PyPzH and 4-PyPzH. The compounds form two isotypic series of 3D coordination polymers and exhibit fair thermal stability up to 360 °C. The luminescence properties of all ten compounds were determined in the solid state, with an antenna effect through ligand-metal energy transfer leading to high efficiency of the luminescence displayed by good quantum yields of up to 74 %. The emission is mainly based on ion-specific lanthanide-dependent intra 4 f-4 f transitions for Tb³⁺ : green, Dy³⁺ : yellow, Sm³⁺ : orange-red, Eu³⁺ : red. For the Gd³⁺ -containing compounds, the yellow emission of ligand triplet-based phosphorescence is observed at room temperature and 77 K. Co doping of the Gd-containing frameworks with Eu³⁺ and Tb³⁺ allow further shifting of the chromaticity towards white light emission.

Synthesis, Structure, and Surface Adsorption Characteristics of a Polynuclear MnII,IV-YbIII Complex

The controlled adsorption of polynuclear coordination compounds with specific structural and electronic characteristics on surfaces is crucial for the prospective implementation of molecule-surface interfaces into practical electronic devices. From this perspective, a neutral 3d,4f-coordination cluster [Mn^II₃Mn^IVYb₃O₃(OH)(L·SMe)₃(OOCMe)₉]·2MeCN·3EtOH (1·2MeCN·3EtOH), where L·SMe^- is a Schiff base, has been synthesized and fully characterized and its adsorption on two different solid substrates, gold and graphite, has been studied. The mixed-valence compound with a bilayered metal core structure and the structurally exposed thioether groups exhibits a substantially different surface bonding to metallic gold and semimetallic graphite substrates. While on graphite the adsorption takes place only on distinguished attraction points with a locally increased number of potential bonding sites such as terrace edges and other surface defects, on gold the molecules were found to adsorb rather weakly on randomly distributed adsorption sites of the surface terraces. This entirely different behavior provides important information for the development of advanced surface materials that may enable well-distributed ordered molecular assemblies.

Electronic Structure of Ytterbium(III) Solvates-a Combined Spectroscopic and Theoretical Study

The wide range of optical and magnetic properties of lanthanide(III) ions is associated with their intricate electronic structures which, in contrast to lighter elements, is characterized by strong relativistic effects and spin-orbit coupling. Nevertheless, computational methods are now capable of describing the ladder of electronic energy levels of the simpler trivalent lanthanide ions, as well as the lowest energy term of most of the series. The electronic energy levels result from electron configurations that are first split by spin-orbit coupling into groups of energy levels denoted by the corresponding Russell-Saunders terms. Each of these groups are then split by the ligand field into the actual electronic energy levels known as microstates or sometimes m_J levels. The ligand-field splitting directly informs on the coordination geometry and is a valuable tool for determining the structure and thus correlating the structure and properties of metal complexes in solution. The issue with lanthanide complexes is that the determination of complex structures from ligand-field splitting remains a very challenging task. In this paper, the optical spectra-absorption, luminescence excitation, and luminescence emission-of ytterbium(III) solvates were recorded in water, methanol, dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF). The electronic energy levels, that is, the microstates, were resolved experimentally. Subsequently, density functional theory calculations were used to model the structures of the solvates, and ab initio relativistic complete active space self-consistent field calculations (CASSCF) were employed to obtain the microstates of the possible structures of each solvate. By comparing the experimental and theoretical data, it was possible to determine both the coordination number and solution structure of each solvate. In water, methanol, and N,N-dimethylformamide, the solvates were found to be eight-coordinated and have a square antiprismatic coordination geometry. In DMSO, the speciation was found to be more complicated. The robust methodology developed for comparing experimental spectra and computational results allows the solution structures of homoleptic lanthanide complexes to be determined.

Leveraging Surface Siloxide Electronics to Enhance the Relaxation Properties of a Single-Molecule Magnet

Single-molecule magnets (SMMs) hold promise for unmatched information storage density as well as for applications in quantum computing and spintronics. To date, the most successful SMMs have been organometallic lanthanide complexes. However, their surface immobilization, one of the requirements for device fabrication and commercial application, remains challenging due to the sensitivity of the magnetic properties to small changes in the electronic structure of the parent SMM. Thus, finding controlled approaches to SMM surface deposition is a timely challenge. In this contribution we apply the concept of isolobality to identify siloxides present at the surface of partially dehydroxylated silica as a suitable replacement for archetypal ligand architectures in organometallic SMMs. We demonstrate theoretically and experimentally that isolated siloxide anchoring sites not only enable successful immobilization but also lead to a 2 orders of magnitude increase in magnetization relaxation times.

The anisotropy of the internal magnetic field on the central ion is capable of imposing great impact on the quantum tunneling of magnetization of Kramers single-ion magnets

In this work, a theoretical method, taking into account the anisotropy of the internal magnetic field (B[combining right harpoon above]int), is proposed to predict the rate of quantum tunneling of magnetization (QTM), i.e., τQTM-1, for Kramers single-ion magnets (SIMs). Direct comparison to both experimental and previous theoretical results of three typical Kramers SIMs indicates the necessity of the inclusion of the anisotropy of B[combining right harpoon above]int for accurate description of QTM. The predictions of the method here are consistent with the theory proposed by Prokof'ev and Stamp (PS). For Kramers SIMs of high magnetic axiality, the QTM rates, predicted by the method here, are almost linearly proportional to the results by the PS method. The dependence of τQTM-1 on various parameters is analyzed for model systems. The averaged magnitude of B[combining right harpoon above]int (Bave) and principal g value of the axial direction (gZ) are the parameters on which τQTM-1 is linearly dependent. The ones on which τQTM-1 is quadratically dependent are gXY, i.e., the principal g value of the transversal direction, and xaniso characterizing the anisotropy of B[combining right harpoon above]int. Compared to Bave and gZ, gXY and xaniso provide a higher order of dependence for QTM. Therefore regulation of the SMM property via introduction of desired values of gXY and xaniso ought to be a strategy more efficient than the one via Bave and gZ. Being different from the one via gXY, the strategy via xaniso to regulate the QTM has been rarely touched upon according to our best knowledge. However, this strategy could also lead to significant improvement since it is the same as gXY in the aspect of the dependence of τQTM-1.

The construction of dynamic dysprosium-carboxylate ribbons by utilizing the hybrid-ligand conception

By utilizing the hybrid-ligand conception, three novel dysprosium complexes Dy(2-py-4-pmc)(L)(H2O) (H2-py-4-pmc = 2-(2-pyridyl)pyrimidine-4-carboxylic acid; L = fumarate (fum, 1), succinate (suc, 2), or pimelate (pim, 3)) have been successfully synthesized. Structural analysis reveals that the dicarboxylate ligands connect 2-py-4-pmc--protected Dy3+ to form one-dimensional molecular ribbons. Magnetic measurements indicate that the three complexes exhibit typical slow magnetic relaxation under a zero dc field with effective reversal barriers Ueff of 180 K, 145 K and 137 K for 1-3, respectively, which is mainly attributed to the strong Ising anisotropy of dysprosium ions induced by the appropriate arrangement of carboxylate groups. Ab initio calculations demonstrate that the charge distribution around dysprosium ions and the magnetic interactions between them are key contributions to their different dynamic behaviour.

Solvent responses and substituent effects upon magnetic properties of mononuclear DyIII compounds

Solvent responsive magnets comprise a class of molecule-based materials where lattice solvent driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of magnet where single-crystal to single-crystal (SCSC) transformations within mononuclear DyIII compounds result in the switching of DyIII single-molecule magnets (SMMs). This structural transformation involves lattice solvents which leads to significant changes in the color and magnetic properties. Additionally, the relaxation dynamics of mononuclear DyIII compounds are perceptibly fine-tuned by the modification of β-diketonate ligands. The uniaxial magnetic anisotropies, magneto-structural correlations and the relaxation mechanism were investigated by magnetic studies and ab initio calculations. These experimental and theoretical studies indicate that compound 2 exhibits the best magnetic properties in compounds 1-4. The experimental observation is supported by the theoretical prediction of QTM time (τZeeQTM) as theτZeeQTM of 2 is remarkably longer than those of the other three compounds by an order of magnitude. This means that, compared with 1, 3, and 4, the magnetic relaxation of 2 is significantly slower. Meanwhile, 2 has the largest value of axial ESP (the axial electrostatic potential), which supports the smallest gXY value in these compounds, resulting in better SMM properties. The present results offer a systematic synthesis regulation to change the magnetization dynamics and further understand magneto-structural correlations for DyIII SMMs.

In Situ Ligand Formation in the Synthetic Processes from Mononuclear Dy(III) Compounds to Binuclear Dy(III) Compounds: Synthesis, Structure, Magnetic Behavior, and Theoretical Analysis

Guided by the self-assembled process and mechanism, the strategy of in situ Schiff base reaction would be capable of bringing a feasible method to construct and synthesize lanthanide compounds with distinct structures and magnetic properties. A mononuclear Dy(III) compound was synthesized through a multidentate Schiff base ligand and a chelating β-diketonate ligand, which was named as [Dy(L)(bppd)]·CH₃OH [1; H₂L = N,N'-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and bppd = 3-bis(pyridin-2-yl)propane-1,3-dione]. Furthermore, a new binuclear Dy(III) compound, [Dy₂(H₂Lox)(bppd)₃]·8CH₃OH [2; H₄Lox = N,N'-bis[2-hydroxy-5-methyl-3-(hydroxyiminomethyl)benzyl]-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine], was obtained via an in situ synthetic process. Under similar synthetic conditions, [Dy(L)(ctbd)] [3; ctbd = 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione] and [Dy₂(H₂Lox)(ctbd)₃]·CH₃OH·C₄H₁₀O (4) were synthesized by modifying the β-diketonate ligand and in situ Schiff base reaction. Compound 3 is a mononuclear configuration, while compound 4 exhibits a binuclear Dy(III) unit. Therein, formylbenzyl groups of H₂L in 1 and 3 were changed to (hydroxyiminomethyl)benzyl groups in 2 and 4, respectively. In isomorphous 2 and 4, two Dy(III) centers are connected through two phenol O^- atoms of the H₂Lox^2- ligand to form a binuclear structure. Eight-coordinated Dy(III) ions with different distortions can be observed in 1-4. The crystals of 1 and 3 suffered dissolution/precipitation to obtain 2 and 4, respectively. The relationship between the structure and magnetism in compounds 1-4 was discussed through the combination of structural, experimental, and theoretical investigations. Especially, the rates of quantum tunneling of magnetization of 1-4 were theoretically predicted and are consistent with the experimental results. For 2 and 4, the theoretically calculated dipolar parameters J_dip are consistent with the experimental observation of weak ferromagnetic coupling.

Tuning magnetic anisotropy via terminal ligands along the Dy⋯Dy orientation in novel centrosymmetric [Dy2] single molecule magnets

The SMM properties of four dinuclear Dy^III complexes can be effectively tuned by the appropriate alteration of terminal ligands and lattice guests.

High magnetization reversal barriers in luminescent dysprosium octahedral and pentagonal bipyramidal single-molecule magnets based on fluorinated alkoxide ligands

We report the synthesis and structures of three luminescent dysprosium(iii) complexes based on fluorinated alkoxide ligands of formulas [Dy(L1)2(THF)4][BPh4]·0.5THF (1), [Dy(L2)2(THF)5][BPh4]·2.5THF (2) and [Dy(L3)2(THF)5][BPh4]·2THF (3) (L1 = (CF3)3CO-, L2 = C6F5C6F4O-, L3 = C6F5C(CH3)O-). Despite the different dysprosium ion geometries (octahedral vs. distorted pentagonal bipyramidal), these systems exhibit a single-molecule magnet (SMM) behavior, but with distinct relaxation dynamics. Moreover, a typical dysprosium-based luminescence is observed for the three complexes, which make them bifunctional magneto-luminescent SMMs. Remarkably, complex 3 exhibits a high anisotropy barrier of 1469 cm-1 and a blocking temperature of 22 K, making it one of the most performant alkoxide-based SMMs with the highest blocking temperature for a luminescent SMM.

The influence of organic bases and substituted groups on coordination structures affording two mononuclear Dy(iii) single-molecule magnets (SMMs) and a novel Dy(iii)–K(i) compound with unusually coordinated fluorine atoms

The different organic bases and substituted groups of auxiliary ligands play an important role in synthetic processes, finally affording distinct structures and magnetic properties.

Tuning the coordination sphere of octahedral Dy(iii) complexes with silanolate/stannanolate ligands: synthesis, structures and slow relaxation of the magnetization

This study reports four SMMs based on silanolate or stannanolate ligands cis-[Dy(OSiPh3)2(THF)4][BPh4]·THF·C6H6 (1), cis-[Dy(OSnPh3)2(THF)4][BPh4]·THF·C6H6·C6H14 (2), fac-[Dy(OSiPh3)3(THF)3]·THF (3) and fac-[Dy(OSiPh3)3(bipy)(THF)]·THF (4).

Regulating the magnetic dynamics of mononuclear β-diketone Dy(iii) single-molecule magnets through the substitution effect on capping N-donor coligands

Substituent change modulates the coordination symmetries and magnetic dynamics of five mononuclear β-diketonate-Dy(iii) complexes with capping N-donor coligands, which is studied by the combination of magnetic investigation and ab initio calculation.

Synthesis, structures and magnetic properties of dysprosium(iii) complexes based on amino-bis(benzotriazole phenolate) and nitrophenolates: influence over the slow relaxation of the magnetization

Field-induced slow relaxation in dysprosium amino-bis(benzotriazole) phenolate complexes.

An unusual mechanism of building up of a high magnetization blocking barrier in an octahedral alkoxide Dy3+-based single-molecule magnet

We report a new octahedral luminescent SMM exhibiting massive crystal-field splitting and an anisotropic barrier of 1385 cm⁻¹.

Lanthanoid pyridyl-β-diketonate 'triangles'. New examples of single molecule toroics

Trinuclear lanthanoid clusters have been synthesised and investigated as toroidal spin systems. A pyridyl functionalised β-diketonate, 1,3-bis(pyridin-2-yl)propane-1,3-dione (o-dppdH) has been used to synthesise a family of clusters of the form [Dy3(OH)2(o-dppd)3Cl2(H2O)4]Cl2·7H2O (1), [Tb3(o-dppd)3(μ3-OH)2(CH3CH2OH)3Cl3][Tb3(o-dppd)3(μ3-OH)2(H2O)(CH3CH2OH)2Cl3]Cl2·H2O (2), [Ho3(OH)2(o-dppd)3Cl(H2O)5]Cl3·3H2O (3) and [Er3(OH)2(o-dppd)3Cl2(H2O)3(CH3OH)]Cl2·3H2O·CH3OH (4). Despite the previous occurrence of this structural motif in the literature, these systems have not been widely investigated in terms of torodic behaviour. Magnetic studies were used to further characterise the complexes. DC susceptibility studies support weak antiferromagnetic exchange in the complexes. Slow magnetic relaxation behaviour is observed in the dynamic AC magnetic studies for complex 1. Theoretical studies predict that complex 1 and 3 have a non-magnetic ground state based on a toroidal arrangement of spins. Changes to the coordination environment in 2 do not support a toroic spin state. The prolate nature of the ErIII centres in complex 4 and large transverse anisotropy do not support the toroidal arrangement of lanthanoid spins in the complex.