Recent advances in luminescent lanthanide based Single-Molecule Magnets

Photoluminescence and magnetic properties of isostructural europium(III), gadolinium(III) and terbium(III) oxamate-based coordination polymers

Developing and investigating advanced multifunctional materials with magnetic properties as candidates for assembling spin qubits for quantum computing is imperative. A new polytopic ligand based on oxamate and aniline was used to promote the synthesis of three neutral homometallic lanthanide-coordinated polymers. New complexes with the formula {Ln(phox)3(DMSO)2(H2O)}n, where Ln = Eu3+ (1), Gd3+ (2), and Tb3+ (3) [phox = N-(phenyl)oxamate and DMSO = dimethylsulfoxide], were synthesized and well characterized by spectroscopic methods as well as X-ray crystallographic analysis. All crystalline structures comprise neutral zigzag chains. The lanthanide ions are linked by three phox ligands, in which two oxygen atoms from two different ligands are responsible for connecting the trivalent lanthanide ions, and one phox ligand completes the coordination sphere in a bis-bidentate mode, together with two DMSO molecules and one water coordination molecule. The coordination sphere of lanthanide ions consisted of spherical capped square antiprism (CSAPR-9) symmetry. The magnetic properties of 1-3 were investigated in the 2-300 K temperature range. The dynamic (ac) magnetic properties of 2 reveal a frequency dependence involving the phonon bottleneck mechanism below 33 K under nonzero applied dc magnetic fields, resulting in an example of a field-induced single-molecule magnet. Solid-state photophysical measurements for Eu3+ (1) and Tb3+ (3) complexes indicate that the N-(phenyl)oxamate ligands are very efficient in sensitizing the lanthanide(III) ions in the visible region of the electromagnetic spectrum. Compounds 1 and 3 exhibited an emission in the red and green regions, respectively. Experimental results and theoretical calculations using the Sparkle/RM1 method support a quantum efficiency of ∼72% for 1, suggesting its potential as a candidate for light conversion molecular devices (LCMDs).

Electronic Structure of a Neodymium(III) Tris(oxidiacetate) Complex from Luminescence Data and Ab Initio Calculations

Neodymium(III) is a near-infrared emissive and magnetic ion, which has found use in various high-technology applications. Yet, accurate predictions of the luminescent and magnetic properties of neodymium(III) based on the coordination environment remain to be done. Guidelines exist, but to build structure-property relationships for this element, more data are needed. Herein, we present a high-symmetry starting point. The tris(oxidiacetate) complex of neodymium(III) was prepared and crystallized, and access to the experimentally determined structure allowed us to quantify the symmetry of the compound and to perform calculations directly on the same structure that is investigated experimentally. The luminescent properties were determined and the electronic structure was computed using state-of-the-art ab initio methods. All electronic transitions in the range from 490 to 1400 nm were mapped experimentally. Using a Boltzmann population analysis, the combination of the excitation and emission spectra revealed the crystal field splitting of the 18 lowest-energy Kramers levels that experimentally could be unambiguously resolved. This assignment was supported by ab initio calculations, and the crystal field splitting was well reproduced. The electronic structure reported for the tris(oxidiacetate) complex was used to deduce the coordination structure in aqueous solution. Finally, the results are compared to empirical trends in the literature for the electronic structure of neodymium(III).

Triple-Decker Hexaazamacrocyclic Lanthanide(III) Complexes: Structure, Magnetic Properties, and Temperature-Dependent Luminescence

The reaction of fluoride anions with mononuclear rare-earth(III) complexes of the hexaazamacrocycle derived from 2,6-diformylpyridine and ethylenediamine affords trinuclear coordination compounds [Ln3L3(μ2-F)4(NO3)2](NO3)3. The X-ray crystal structures of these complexes show triplex cationic complexes where the three roughly parallel macrocyclic lanthanide(III) units are linked by bis-μ2-F bridges. The detailed analysis of the photophysical properties of the [Eu3L3(μ2-F)4(NO3)2](NO3)3·2H2O and [Tb3L3(μ2-F)4(NO3)2](NO3)3·3H2O complexes reveals different temperature dependence of luminescence intensity and luminescence decay time of the Eu(III) and Tb(III) derivatives. The spectra of mixed species of average composition [Eu1.5Tb1.5L3(μ2-F)4(NO3)2](NO3)3·3H2O are in accordance with the ratiometric luminescent thermometer behavior. Measurements of the direct-current (dc) magnetic susceptibility of the [Dy3L3(μ2-F)4(NO3)2](NO3)3·2H2O complex indicate possible ferromagnetic interactions between the Dy(III) ions. Alternating current (ac) susceptibility measurements of this complex indicate single-molecule magnet behavior in zero dc field with magnetic relaxation dominated by Orbach mechanism and an effective energy barrier Ueff = 12.3 cm-1 (17.7 K) with a pre-exponential relaxation time, τ0 of 7.3 × 10-6 s. A similar reaction of mononuclear macrocyclic complexes with a higher number of fluoride equivalents results in polymeric {[Ln3L3(μ2-F)5](NO3)4}n complexes. The X-ray crystal structure of the Nd(III) derivative of this type shows trinuclear units that are additionally linked by single fluoride bridges to form a linear coordination polymer.

Evaluation of Point Group Symmetry in Lanthanide(III) Complexes: A New Implementation of a Continuous Symmetry Operation Measure with Autonomous Assignment of the Principal Axis

The structure of molecular systems dictates the physical properties, and symmetry is the determining factor for all electronic properties. This makes group theory a powerful tool in quantum mechanics to compute molecular properties. For inorganic compounds, the coordination geometry has been estimated as idealized polyhedra with high symmetry, which, through ligand field theory, provides predictive capabilities. However, real samples rarely have ideal symmetry, and although continuous shape measures (CShM) can be used to evaluate deviation from an ideal reference structure σideal, this often fails for lanthanide(III) complexes with high coordination numbers, no obvious choice of principal axes, and no obvious reference structure. In lanthanide complexes, the unique electronic structures and associated properties are intricately tied to the symmetry around the lanthanide center. Therefore, robust methodologies to evaluate and estimate point group symmetry are instrumental for building structure-property relationships. Here, we have demonstrated an algorithmic approach that orients a molecular structure Q in the best possible way to the symmetry axis of any given point group G and computes a deviation from the ideal symmetry σsym(G,Q). This approach does not compute the deviation from an ideal reference system, but the intrinsic deviation in the structure induced by symmetry operations. If the structure contains the symmetry operation, there is no deviation and σsym(G,Q) = 0. The σsym deviation is generated from all of the symmetry operation ÔS in a point group G using the most correct orientation of the sample structure in each group G. The best orientation is found by an algorithm that minimizes the orientation of the structure with respect to G. To demonstrate the methodology, we have investigated the structure and symmetry of 8- and 9-coordinated lanthanide(III) aqua complexes and correlated the luminescence from 3 europium(III) crystals to their actual symmetry. To document the methodology, the approach has been tested on 26 molecules with different symmetries. It was concluded that the method is robust and fully autonomous.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Excitation wavelength-dependent lanthanide-disalicylaldehyde coordination hybrid capable of distinguishing D2O from H2O

The increasing demands in fields of anti-counterfeiting, fluorescence analysis, clinical therapy and LED illumination are urgently eager for more excellent optically switchable luminescent materials with the stable and multimodal fluorescence in single-component matrix. Herein, the lanthanide-disalicylaldehyde coordination hybrid H2Qj4/TbxEuy is proposed as an efficient luminescent matrix to connect terbium sensibilization with ESIPT (excited-state intramolecular proton transfer) effects, and three multi-emission hybrids are finally designed and synthesized by regulating Tb3+ and Eu3+ ratios. Surprisingly, the H2Qj4/Tb0.91Eu0.09 shows the excitation wavelength-dependent luminescence in solution which originates from two energy transfer ways of terbium sensibilization effect. It exhibits green and red lights under the 369 and 394 nm UV lamp, respectively. Three hybrids are further used as lab-on-a-molecule fluorescent probes to perform multianalyte detection for various solvents by selected fluorescent sensing channels. By means of PCA (principal component analysis) and HCA (hierarchical cluster analysis), all of them can successfully detect and discriminate17 common solvents, especially the H2O and D2O. Moreover, the H2Qj4/Tb0.91Eu0.09 also shows the wide linear responses of H2O content in D2O, discrimination of two-component solvent mixtures, hygroscopicity evaluation of D2O and information encryption which will advance the progress of multimodal luminescent materials and multianalyte chemosensors.

Luminescent Er3+ based single molecule magnets with fluorinated alkoxide or aryloxide ligands

We report the synthesis, structures, and magnetic and luminescence properties of a series of new mono- and dinuclear Er3+ complexes derived from sterically demanding aryloxide and fluorinated alkoxide ligands: [4-tBu-2,6-(Ph2CH)2C6H2O]3Er(THF) (1), [(C6F5)3CO]3Er(Me3SiOH) (2), [(C6F5)3CO]3Er[(Me3Si)2NH] (3), [(C6F5)3CO]3Er(C6H5CH3) (4), [(C6F5)3CO]3Er(o-Me2NC6H4CH3) (5) and {[Ph(CF3)2CO]2Er(μ2-OC(CF3)2Ph)}2 (6). In compounds 1, 2, and 4, the Er3+ ion is four-coordinated and adopts a distorted trigonal pyramidal geometry, while in 3, 5, and 6, the coordination geometry of Er3+ is impacted by the presence of several relatively short Er⋯F distances, making them rather 6-coordinated. All compounds behave as field-induced Single Molecule Magnets (SMMs) and exhibit an Er3+ characteristic near infrared (NIR) emission associated with the 4I13/2 → 4I15/2 transition with a remarkably long lifetime going up to 73 μs, which makes them multifunctional luminescent SMMs. The deconvolution of the NIR emission spectra allowed us to provide a direct probe of the crystal field splitting in these compounds, which was correlated with magnetic data.

Water-Mediated Charge Transfer and Electron Localization in a Co3Fe2 Cyanide-Bridged Trigonal Bipyramidal Complex

The effects of temperature and chemical environment on a pentanuclear cyanide-bridged, trigonal bipyramidal molecular paramagnet have been investigated. Using element- and oxidation state-specific near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS) to probe charge transfer and second order, nonlinear vibrational spectroscopy, which is sensitive to symmetry changes based on charge (de)localization coupled with DFT, a detailed picture of environmental effects on charge-transfer-induced spin transitions is presented. The molecular cluster, Co3Fe2(tmphen)6(μ-CN)6(t-CN)6, abbrev. Co3Fe2, shows changes in electronic behavior depending on the chemical environment. NAP-XPS shows that temperature changes induce a metal-to-metal charge transfer (MMCT) in Co3Fe2 between a Co and Fe center, while cycling between ultrahigh vacuum and 2 mbar of water at constant temperature causes oxidation state changes not fully captured by the MMCT picture. Sum frequency generation vibrational spectroscopy (SFG-VS) probes the role of the cyanide ligand, which controls the electron (de)localization via the superexchange coupling. Spectral shifts and intensity changes indicate a change from a charge delocalized, Robin-Day class II/III high spin state to a charge-localized, class I low spin state consistent with DFT. In the presence of a H-bonding solvent, the complex adopts a localized electronic structure, while removal of the solvent delocalizes the charges and drives an MMCT. This change in Robin-Day classification of the complex as a function of chemical environment results in reversible switching of the dipole moment, analogous to molecular multiferroics. These results illustrate the important role of the chemical environment and solvation on underlying charge and spin transitions in this and related complexes.

Covalency versus magnetic axiality in Nd molecular magnets: Nd-photoluminescence, strong ligand-field, and unprecedented nephelauxetic effect in fullerenes NdM2N@C80 (M = Sc, Lu, Y)

Nd-based nitride clusterfullerenes NdM2N@C80 with rare-earth metals of different sizes (M = Sc, Y, Lu) were synthesized to elucidate the influence of the cluster composition, shape and internal strain on the structural and magnetic properties. Single crystal X-ray diffraction revealed a very short Nd-N bond length in NdSc2N@C80. For Lu and Y analogs, the further shortening of the Nd-N bond and pyramidalization of the NdM2N cluster are predicted by DFT calculations as a result of the increased cluster size and a strain caused by the limited size of the fullerene cage. The short distance between Nd and nitride ions leads to a very large ligand-field splitting of Nd3+ of 1100-1200 cm-1, while the variation of the NdM2N cluster composition and concomitant internal strain results in the noticeable modulation of the splitting, which could be directly assessed from the well-resolved fine structure in the Nd-based photoluminescence spectra of NdM2N@C80 clusterfullerenes. Photoluminescence measurements also revealed an unprecedentedly strong nephelauxetic effect, pointing to a high degree of covalency. The latter appears detrimental to the magnetic axiality despite the strong ligand field. As a result, the ground magnetic state has considerable transversal components of the pseudospin g-tensor, and the slow magnetic relaxation of NdSc2N@C80 could be observed by AC magnetometry only in the presence of a magnetic field. A combination of the well-resolved magneto-optical states and slow relaxation of magnetization suggests that Nd clusterfullerenes can be useful building blocks for magneto-photonic quantum technologies.

Novel stable ytterbium acetylacetonate-quinaldinate complexes as single-molecule magnets and surprisingly efficient luminophores

The first Yb complexes comprising a quinoline-2-carboxylate (quinaldinate, Q-) ligand, namely 1D-polymeric [Yb(acac)2(Q)]n (1, acac- is the acetylacetonate (pentane-2,4-dionate) anion) and mononuclear [Yb(acac)2(Q)(Phen)] (2, Phen is 1,10-phenanthroline), are reported. The bifunctionality of both complexes as field-induced single-molecule magnets (SMMs) and near IR luminophores has been revealed. The SMM properties of 1 and 2 have been discussed in terms of the geometry and composition of the coordination environment. Also, 1 is the first example of 1D-polymeric SMMs with the capped octahedral surrounding of Yb3+. The photoluminescence quantum yields (PLQYs) of 1 and 2 are 2 and 4%, respectively. The origins of this difference are discussed. Surprisingly, the PLQY value of 2 is high for compounds comprising a lot of C-H vibrational quenchers, being the highest one for reliably characterized Yb β-diketonate complexes, and surpassing those for complexes with a broad range of anionic ligands. In this respect, the role of the Phen ligand is to tune the coordination mode of Q- thereby decreasing the energy of coordinating C-O oscillators rather than to act as a typical antenna ligand. These results can give rise to an alternative route to elaborate efficient Yb-based luminophores via the substitution of the β-diketonate ligands controlled by the introduction of appropriate neutral ligands.

Utility of all-pyrazole heteroscorpionates in f-element chemistry

Since their discovery in 1966, scorpionate ligands have been utilized to make coordination compounds for a variety of applications such as: studying organometallic reactions, biomimetic complexes, light-emitting materials and single-ion magnets. The recent development of a solvent-free pyrazole substitution chemistry has yielded the quantitative synthesis of asymmetrically functionalized all-pyrazole heteroscorpionate ligands. In this frontier article, we highlight the utility of all-pyrazole heteroscorpionates, specifically, nitro-trispyrazolylborates, in f-element chemistry. They offer great versatility in coordinating ability, donor strength, steric bulk and even optical charge transfer properties, all of which can be used to tune the properties of resultant complexes with metal ions. We show how they can impart structural diversity, sensitize Ln3+ luminescence and engender magnetic anisotropy and slow magnetic relaxation in the ion they coordinate. Additionally, we comment on the future of functionalized trispyrazolyl scorpionates, which includes enabling post-synthetic modifications of f-element complexes and becoming a platform to study the electronic properties of low oxidation state actinides.

Origin of Weak Magnetic Coupling in a Dimanganese(II) Complex Bridged by the Tetrathiafulvalene-Tetrathiolate Radical

Magnetic exchange coupling (J) between different spin centers plays a crucial role in molecule-based magnetic materials. Direct exchange coupling between an organic radical and a metal is frequently stronger than superexchange through diamagnetic ligands, and the strategy of using organic radicals to engender desirable magnetic properties has been an area of active investigation. Despite significant advances and exciting bulk properties, the magnitude of J for radical linkers bridging paramagnetic centers is still difficult to rationally predict. It is thus important to elucidate the features of organic radicals that govern this parameter. Here, we measure J for the tetrathiafulvalene-tetrathiolate radical (TTFtt3-•) in a dinuclear Mn(II) complex. Magnetometry studies show that the antiferromagnetic coupling in this complex is much weaker than that in related Mn(II)-radical compounds, in contrast to what might be expected for the S-based chelating donor atoms of TTFtt. Experimental and computational analyses suggest that this small J coupling may be attributed to poor overlap between Mn- and TTFtt-based magnetic orbitals coupled with insignificant spin density on the coordinating S-atoms. These factors override any expected increase in J from the comparatively strong S-donors. This work elucidates the magnetic coupling properties of the TTFtt3-• radical for the first time and also demonstrates how multiple competing factors must be considered in rationally designing organic radical ligands for molecular-based magnetic compounds.

Field induced single ion magnet behavior in CoII complexes in a distorted square pyramidal geometry

We report three CoII-based complexes with the general formula [CoII(L)(X)2] by changing the halide/pseudo-halide ions [X = NCSe (1SeCN); Cl (2Cl) and Br (3Br)]. The obtained τ5 and CShM values confirm a distorted square pyramidal geometry around the CoII ion in all these complexes. In these three complexes, the central CoII ion is situated above the basal plane of the square pyramidal geometry. The extent of distortion from the ideal SPY-5 geometry differs upon changing the coordinating halide/pseudo-halide ion in these complexes. This essentially results in the alteration of the anisotropic parameter D and hence impacts the magnetic properties in these complexes. This phenomenon has been corroborated with the aid of theoretical investigations. All these complexes display field-induced SIM behaviour with magnetic relaxation occurring through a combination of processes depending on the applied dc magnetic field values and dilution.

Single molecule magnet features in luminescent lanthanide coordination polymers with heptacoordinate Dy/Yb(III) ions as nodes

Two sets of 1D/2D lanthanide coordination polymers with formulas of Ln(oqa)3·2H2O [Hoqa = 2-(4-oxoquinolin-1(4H)-yl) acetic acid, Ln = Dy (1), Yb (2)] and Ln(oaa)2(HCOO)(H2O) [Hoaa = 2-(9-oxoacridin-10(9H)-yl) acetic acid, Ln = Dy (3), Yb (4)] have been synthesized and their physical properties were investigated. All four complexes are constructed from seven-coordinate lanthanide ions and corresponding organic linkers. The lanthanide ions in 1 and 2 adopt a pentagonal bipyramid coordination geometry, whereas the coordination geometry of lanthanide ions in 3 and 4 can be described as a capped octahedron. Slow magnetic relaxation behaviors were observed in these four products at a zero/non-zero static magnetic field. Complexes 1, 2 and 4 exhibit the characteristic emission of Ln(III) ions, whereas complex 3 shows ligand-based emission. Bright yellow light emission was also observed when a voltage was applied, demonstrating the potential of 1 for application in light-emitting diodes (LEDs). Compounds 3 and 4 are the first examples of lanthanide complexes based on Hoaa ligands.

Tetranuclear lanthanide-based silsesquioxanes: towards a combination of a slow relaxation of the magnetization and a luminescent thermometry

Lanthanide-based silsesquioxanes constitute an emerging family of cage-like metallasilsesquioxanes with exciting optical and magnetic properties. We report here the synthesis, structures and luminescence properties of a series of tetranuclear lanthanide-silsesquioxane compounds of general formula [NEt4]2[(Ph4Si4O8)2(Ln/Ln')4(NO3)6(EtOH)2(MeCN)2]·4(MeCN) with different lanthanide ions (where Ln/Ln' = Dy3+/Eu3+ (1), Dy3+/Tb3+ (2) and Eu3+/Tb3+/Y3+ (3)) and investigate the impact of the lanthanide ions combination on magnetic and photo-luminescent properties. Compound 1 behaves as a field-induced Single Molecule Magnet (SMM) and presents temperature-dependent luminescence characteristics of Eu3+ making it an emissive thermometer working in the temperature range 293-373 K with the maximum relative sensitivity of 1.15% K-1 achieved at 293 K. Compounds 2 and 3 are paramagnets, which demonstrate a characteristic photoluminescence with Dy3+ to Tb3+ and Tb3+ to Eu3+ energy transfers, respectively.

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.

Desolvation-Induced Highly Symmetrical Terbium(III) Single-Molecule Magnet Exhibiting Luminescent Self-Monitoring of Temperature

A conjunction of Single-Molecule Magnet (SMM) behavior and luminescence thermometry is an emerging research line aiming at contactless read-out of temperature in future SMM-based devices. The shared working range between slow magnetic relaxation and the thermometric response is typically narrow or absent. We report TbIII -based emissive SMMs formed in a cyanido-bridged framework whose properties are governed by the reversible structural transformation from [TbIII (H2 O)2 ][CoIII (CN)6 ] ⋅ 2.7H2 O (1) to its dehydrated phase, TbIII [CoIII (CN)6 ] (2). The 8-coordinated complexes in 1 show the moderate SMM effect but it is enhanced for trigonal-prismatic TbIII complexes in 2, showing the SMM features up to 42 K. They are governed by the combination of QTM, Raman, and Orbach relaxation with the energy barrier of 594(18) cm-1 (854(26) K), one of the highest among the TbIII -based molecular nanomagnets. Both systems exhibit emission related to the f-f electronic transitions, with the temperature variations resulting in the optical thermometry below 100 K. The dehydration leads to a wide temperature overlap between the SMM behavior and thermometry, from 6 K to 42 K. These functionalities are further enriched after the magnetic dilution. The role of post-synthetic formation of high-symmetry TbIII complexes in achieving the SMM effect and hot-bands-based optical thermometry is discussed.

[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.

A trivalent 4f complex with two bis-silylamide ligands displaying slow magnetic relaxation

The best-performing single-molecule magnets (SMMs) have historically relied on pseudoaxial ligands delocalized across several coordinated atoms. This coordination environment has been found to elicit strong magnetic anisotropy, but lanthanide-based SMMs with low coordination numbers have remained synthetically elusive species. Here we report a cationic 4f complex bearing only two bis-silylamide ligands, Yb(III)[{N(SiMePh₂)₂}₂][Al{OC(CF₃)₃}₄], which exhibits slow relaxation of its magnetization. The combination of the bulky silylamide ligands and weakly coordinating [Al{OC(CF₃)₃}₄]^- anion provides a sterically hindered environment that suitably stabilizes the pseudotrigonal geometry necessary to elicit strong ground-state magnetic anisotropy. The resolution of the m_J states by luminescence spectroscopy is supported by ab initio calculations, which show a large ground-state splitting of approximately 1,850 cm^-1. These results provide a facile route to access a bis-silylamido Yb(III) complex, and further underline the desirability of axially coordinated ligands with well-localized charges for high-performing SMMs.

Tuning the optical and magnetic properties of lanthanide single-ion magnets using nitro-functionalized trispyrazolylborate ligands

We report the synthesis, crystal structures, photophysical and magnetic properties of 11 novel lanthanide complexes with the asymmetrically functionalized trispyrazolylborate ligand 4-nitrotrispyrazolylborate, 4-NO₂Tp^-: [Ln(4-NO₂Tp)₃] (Ln = La-Dy, except Pm). In-depth photophysical characterization of the ligands via luminescence, reflectance and absorption spectroscopic techniques, decay lifetimes, quantum yields supported by time-dependent density functional theory (TD-DFT) and natural bond order (NBO) analysis reveal that n-NO₂Tp^- ligands are dominated by intra-ligand charge transfer (ILCT) transitions and that second-sphere interactions are critical to the stabilization of the T₁ state of n-NO₂Tp^- ligands and hence their ability to sensitize Ln³⁺ emission. The luminescence properties of the complexes indicate that 4-NO₂Tp^- is a poor sensitizer of Ln³⁺ emission, unlike 3-NO₂Tp^-. Moreover, [Nd(4-NO₂Tp)₃] (crystallized as a hexane solvate) displays single-molecule magnet (SMM) properties, with longer relaxation times and larger barrier than the non-functionalized [NdTp₃], attributed to the addition of the NO₂-group and subsequent rigidification of the molecular structure.

Thiacalix[4]arene-Sandwiched Sandglass-like Ln9 Clusters (Ln = Tb and Eu): Insights into the Selective Luminescence Quenching Properties by p-Nitrobenzene Derivatives

Nonanuclear lanthanide clusters Ln₉ (Ln = Tb and Eu) based on p-tert-butylthiacalix[4]arene (H₄TC4A) have been synthesized by the solvothermal reaction and were structurally determined by single-crystal X-ray diffraction. The framework of Ln₉ can be termed as a sandglass-like structure whose two Ln₄-TC4A polynuclear secondary building units are bridged by one octa-coordinate {Ln(μ₃-O)₈} unit. Efficient TC4A-to-Ln energy transfer was observed for Tb₉ but not for Eu₉. The luminescence quantum yield (QY) of Tb₉ in the solid state at room temperature was determined to be 17.6%, while its highest QY in a methanolic solution (2 × 10^-5 mol/L) is 59.2% upon excitation at 318 nm. The luminescence of Tb₉ was quenched selectively by derivatives of p-nitrobenzene, as demonstrated by the results of photoluminescence and UV-vis titration experiments and supported by density functional theory calculations. We believe that the interactions between the analyte molecules and the pocket of Tb₉ are primarily responsible for the observed quenching. As such, this work represents one of the few examples of utilizing structurally interesting lanthanide cluster complexes as a sensory platform for the recognition of meaningful analytes and portends the further development of lanthanide-calixarene-complex-based functional materials.

Structure and Properties of Heterometallics Based on Lanthanides and Transition Metals with Methoxy-β-Diketonates

The possibility of obtaining volatile polynuclear heterometallic complexes containing lanthanides and transition metals bound by methoxy-β-diketonates was studied. New compounds were prepared by cocrystallization of monometallic complexes from organic solvents. Ln(tmhd)₃ were used as initial monometallic complexes (Ln = La, Pr, Sm, Gd, Tb, Dy, Lu; tmhd = 2,2,6,6-tetramethylheptane-3,5-dionate) in combination with TML₂ in various ratios (TM = Cu, Co, Ni, Mn; L: L¹ = 1,1,1-trifluoro-5,5-dimethoxypentane-2,4-dionate, L² = 1,1,1-trifluoro-5,5-dimethoxy-hexane-2,4-dionate, L³ = 1,1,1-trifluoro-5-methoxy-5-methylhexane-2,4-dionate). Heterometallic complexes of the composition [(LnL₂tmhd)₂TM(tmhd)₂] were isolated for light lanthanides Ln= La, Pr, Sm, Gd, and L= L¹ or L². By single crystal XRD, it has been established that heterometallic compounds containing La, Pr, Cu, Co, and Ni are isostructural linear coordination polymers of alternating mononuclear transition metal complexes and binuclear heteroleptic lanthanide complexes, connected by donor-acceptor interactions between oxygen atoms of the methoxy groups and transition metal atoms. A comparison of powder XRD patterns has shown that all heterometallic complexes obtained are isostructural. Havier lanthanides Ln = Tb, Dy, Lu did not form heterometallics. Instead, homometallic complexes Ln(L³)₃ were identified for Ln = Dy, Lu as well as for Ln = La. The thermal properties of the complexes were investigated by TG-DTA and vacuum sublimation tests. The heterometallic complexes were found to be not volatile and decomposed under heating to produce inorganic composites of TM oxides and Ln fluorides. In contrast, Ln(L³)₃ is volatile and may be sublimed in a vacuum. Results of magnetic measurements are discussed for several heterometallic and homometallic complexes.

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.

Polymorphism modulates photoluminescence and magnetic dynamics of mononuclear dysprosium-anthracene complexes

Complexes α-Dy(depma)₃Cl₃ (α-DyCl), β-Dy(depma)₃Cl₃ (β-DyCl) and β-Dy(depma)₃Br₃ (β-DyBr) (depma = 9-diethylphosphono-methylanthracene) are reported. α-DyCl and β-DyCl are polymorphs showing distinct magnetic dynamics with energy barriers of 32.3 K and 66.6 K. They also show distinct luminescence properties with emission peaks at 487 nm and 530 nm, respectively.

Slow Magnetic Relaxation and Luminescent Properties of Mononuclear Lanthanide-Substituted Keggin-Type Polyoxotungstates with Compartmental Organic Ligands

The reaction of mid to late lanthanide ions with the N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylene-diamine organic ligand and monolacunary Keggin type [α-SiW₁₁O₃₉]^8– anion affords a series of isostructural compounds, namely, K₅[Ln^III(α-SiW₁₁O₃₉)(C₂₀H₂₂Br₂N₂O₄)]·14H₂O (1-Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the Ln^III ion in a biaugmented trigonal prismatic geometry, which occupies the external O₄ site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N₂O₂ coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and π–π interactions established between adjacent molecular units govern the crystal packing, which results in the formation of assemblies containing six hybrid species assembled in a chairlike conformation. 1-Gd and 1-Yb display slow relaxation of the magnetization after the application of an external magnetic field with maxima in the out-of-phase magnetic susceptibility plots below ∼5–6 K, which is ascribed to the presence of various relaxation mechanisms. Moreover, photoluminescent emission is sensitized for 1-Sm and 1-Eu in the visible region and 1-Er and 1-Yb in the NIR. In contrast, the quenching of metal-centered luminescence in the 1-Tb derivative has been attributed to the out-of-pocket coordination mode of the lanthanide center within the POM fragment. It is demonstrated that the 1-Yb dual magneto-luminescent material represents the first lanthanide-containing POM reported to date with simultaneous slow magnetic relaxation and NIR emission. Solution stability of the hybrid molecular species in water is also confirmed by ESI-mass spectrometry experiments carried out for 1-Tb and 1-Tm.

A series of solution stable, molecular polyoxometalate hybrids, namely, [α-SiW₁₁O₃₉Ln^III(C₂₀H₂₂N₂Br₂O₄)]⁵⁻ (Ln^III = Sm to Lu) have been synthesized from the combination of mid-to-late lanthanides, lacunary Keggin-type anions, and a compartmental organic ligand. Metal-centered luminescence in both the visible and NIR region as well as slow relaxation of magnetization was found for different members of this family, including the Yb derivative, which represents the first POM-based system with slow magnetic relaxation and sensitized emission in the NIR region.

3-Pyridylacetic-Based Lanthanide Complexes Exhibiting Magnetic Entropy Changes, Single-Molecule Magnet, and Fluorescence

Four complexes from lanthanides, 3-pyridylacetate, and 1,10-phenanthroline, formulated as [Ln2(3-PAA)2(μ-Cl)2(phen)4](ClO4)2 [Ln = Gd(1), Dy(2), Eu(3), Tb(4), 3-PAA = 3-pyridylacetic acid, phen = 1,10-phenanthroline], were obtained. The four compounds were characterized by IR spectra, thermogravimetric analyses, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1-4 are isomorphous, and they have a dinuclear structure. Magnetic studies reveal that 1 shows the magnetocaloric effect with -ΔS m max = 19.03 J kg-1 K-1 at 2 K for ΔH = 5 T, and 2 displays a field-induced single-molecule magnet with U eff = 19.02 K. The photoluminescent spectra of 3 and 4 exhibit strong characteristic emission, which demonstrate that the ligand-to-EuIII/TbIII energy transfer is efficient.

Deciphering the Role of Symmetry and Ligand Field in Designing Three-Coordinate Uranium and Plutonium Single-Molecule Magnets

Actinide single-molecule magnets (SMMs) have gained paramount interest in molecular magnetism as they offer a larger barrier height of magnetization (U_eff) reversal compared to the lanthanide analogue, thanks to their greater metal-ligand covalency. However, the reported actinide SMMs to date yield a relatively smaller U_eff as there is no established design principle to enhance U_eff values. To address this issue, we have employed ab initio CASSCF/CASPT2/NEVPT2 calculations to study a series of three-coordinate U³⁺ and Pu³⁺ SMMs. To begin with, we have studied two experimentally characterized U³⁺ ion-field-induced SMMs, namely, planar [U{N(SiMe₂^tBu)₂}₃] (1) and pyramidal [U{N(SiMe₃)₂}₃] (2) complexes reported earlier. Both the complexes were found to stabilize m_J = |±1/2⟩ as the ground state with a very strong quantum tunneling of magnetization (QTM), rendering them unsuitable for SMMs. Our calculations reveal that in the pyramidal geometry (such as in 2), the energy of the 5f²6d¹ state is lowered compared to the planar geometry (as in 1), resulting in a slightly better SMM characteristic in the former. To unravel the effect of symmetry in magnetic properties, ab initio calculations were performed on two reported T-shaped complexes [U(NSiⁱPr₂)₂(I)] (3) and [U(NHAr^iPr6)₂I] (4, Ar^iPr6 = 2,6-(2,4,6-iPr₃C₆H₂)₂C₆H₃). Quite interestingly, m_J = |±9/2⟩ is found to be the ground state for both the complexes with a blocking barrier exceeding 900 cm^-1. Furthermore, to decipher the effect of the transuranic element in magnetic anisotropy, ab initio calculations were extended to the Pu analogue of 2, [Pu{N(SiMe₃)₂}₃] (5), which yields a record-breaking blocking barrier of ∼1933 cm^-1. Among the three-coordinate geometries studied, the pyramidal geometry was found to offer substantial magnetic anisotropy for Pu³⁺ ions, while a T-shaped geometry is best suited for U³⁺ ions. While the chosen theoretical protocols' overestimation of barrier height cannot be avoided, these values are still several orders of magnitude larger than the U_eff values reported for any actinide SMMs and unveil a design principle for superior three-coordinate actinide-based SMMs.

Single molecule magnet behavior and luminescence of {Ln4} and {LnZn} complexes

A serials of tetranuclear coordination clusters [Ln4L2(HL)2(μ3-OH)2(NO3)2](NO3)2 [Ln = Dy (1•3CH3CN•5H2O), Gd (2•4CH3CN•5H2O), H2L = 6,6'-dimethoxy-2,2'-[2,2-dimethylpropane-1,3-diylbis-(nitrilomethylidyne)] diphenol] and dinuclear complexes [LnZnL(NO3)3(H2O)]•2CH3CN [Ln = Dy (3), Er (4), Yb (5), Lu...

Opening Magnetic Hysteresis via Improving Planarity of Equatorial Coordination by Hydrogen Bonding

Through a mixed-ligand strategy, the structural change from a discrete dinuclear DyIII cluster to a one-dimensional polymeric chain was achieved, maintaining the two magnetic entities with the same {Dy(dppbO2)2(H2O)5} (dppbO2...

Post-synthetic modification of Prussian blue type nanoparticles: tailoring the chemical and physical properties

This review focuses on recent advances in the post-synthetic modification of nano-sized Prussian blue and its analogues and compares them with the current strategies used in metal–organic frameworks to give future outlooks in this field.

A. Valente D, Cardozo TM, Horta BAC, Mariano DL, Nunes WC, Pedroso EF, Pereira CLM. Lanthanide(iii)-oxamato complexes containing Nd3+ and Ho3+: crystal structures, magnetic properties, and ab initio calculations

Two series of chlorine or fluorine derivatives containing monooxamato ligands result in diamagnetic complexes of Y3+ and La3+ and paramagnetic complexes of Nd3+ and Ho3+ that behave as single-ion magnets at lower temperatures.

Single-Molecule Magnet with Thermally Activated Delayed Fluorescence Based on a Metallofullerene Integrated by Dysprosium and Yttrium Ions

It is vital to construct luminescent single-molecule magnets (SMMs) and explore their applications in quantum computing technique and magneto-luminescence devices. In this work, we report a luminescent single-molecule magnet with thermally activated delayed fluorescence (TADF) based on metallofullerene DyY₂N@C₈₀. DyY₂N@C₈₀ was constructed by integrating dysprosium and yttrium ions into a fullerene cage. Magnetic results suggest that DyY₂N@C₈₀ exhibits magnetic hysteresis loops below 8 K originating from the Dy³⁺ ion. Moreover, DyY₂N@C₈₀ exhibits TADF originating from the Y³⁺-coordinated carbon cage, whose luminescence peak positions and peak intensities can be obviously influenced by Dy³⁺. Furthermore, a supramolecular complex of DyY₂N@C₈₀ and [12]Cycloparaphenylene ([12]CPP) was then prepared to construct a single-molecule magnet with multiwavelength luminescence. The effects of host-guest interaction on photoluminescence properties of DyY₂N@C₈₀ were disclosed. Theoretical calculations were also employed to illustrate the structures of DyY₂N@C₈₀ and DyY₂N@C₈₀⊂[12]CPP.

Tunable magnetic anisotropy in luminescent cyanido-bridged {Dy2Pt3} molecules incorporating heteroligand PtIV linkers

The interest in the generation of photoluminescence in lanthanide(III) single-molecule magnets (SMMs) is driven by valuable magneto-optical correlations as well as perspectives toward magnetic switching of emission and opto-magnetic devices linking SMMs with optical thermometry. In the pursuit of enhanced magnetic anisotropy and optical features, the key role is played by suitable ligands attached to the 4f metal ion. In this context, cyanido complexes of d-block metal ions, serving as expanded metalloligands, are promising. We report two novel discrete coordination systems serving as emissive SMMs, {[Dy^III(H₂O)₃(tmpo)₃]₂[Pt^IVBr₂(CN)₄]₃}·2H₂O (1) and {[Dy^III(H₂O)(tmpo)₄]₂[Pt^IVBr₂(CN)₄]₃}·2CH₃CN (2) (tmpo = trimethylphosphine oxide), obtained by combining Dy^III complexes with uncommon dibromotetracyanidoplatinate(IV) ions, [Pt^IVBr₂(CN)₄]^2-. They are built of analogous Z-shaped cyanido-bridged {Dy₂Pt₃} molecules but differ in the coordination number of Dy^III (C.N. = 8 in 1, C.N. = 7 in 2) and the number of coordinated tmpo ligands (three in 1, four in 2) which is related to the applied solvents. As a result, both compounds reveal Dy^III-centred slow magnetic relaxation but only 1 shows SMM character at zero dc field, while 2 is a field-induced SMM. The relaxation dynamics in both systems is governed by the Raman relaxation mechanism. These effects were analysed using ac magnetic data and the results of the ab initio calculations with the support of magneto-optical correlations based on low-temperature high-resolution emission spectra. Our findings indicate that heteroligand halogeno-cyanido Pt^IV complexes are promising precursors for emissive SMMs with the further potential of sensitivity to external stimuli that may be related to the lability of the axially positioned halogeno ligands.

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.

Combined Experimental and Ab Initio Methods for Rationalization of Magneto-Luminescent Properties of YbIII Nanomagnets Embedded in Cyanido/Thiocyanidometallate-Based Crystals

The ab initio calculations were correlated with magnetic and emission characteristics to understand the modulation of properties of NIR-emissive [Yb^III(2,2'-bipyridine-1,1'-dioxide)₄]³⁺ single-molecule magnets by cyanido/thiocyanidometallate counterions, [Ag^I(CN)₂]^- (1), [Au^I(SCN)₂]^- (2), [Cd^II(CN)₄]^2-/[Cd^II₂(CN)₇]^3- (3), and [M^III(CN)₆]^3- [M^III = Co (4), Ir (5), Fe (6), Cr (7)]. Theoretical studies indicate easy-axis-type ground doublets for all Yb^III centers. They differ in the magnetic axiality; however, transversal g-tensor components are always large enough to explain the lack of zero-dc-field relaxation. The excited doublets lie more than 120 cm^-1 above the ground one for all Yb^III centers. It was confirmed by high-resolution emission spectra reproduced from the ab initio calculations that give reliable insight into energies and oscillator strengths of optical transitions. These findings indicate the dominance of Raman relaxation with the power n varying from 2.93(4) to 6.9(2) in the 4-3-5-1-2 series. This trend partially follows the magnetic axiality, being deeper correlated with the phonon modes schemes of (thio)cyanido matrices.

Modern physical methods for the molecular design of single-molecule magnets

Many paramagnetic metal complexes have emerged as unique magnetic materials (single-molecule magnets), which behave as conventional magnets at the single-molecule level, thereby making it possible to use them in modern devices for data storage and processing. The rational design of these complexes, however, requires a deep understanding of the physical laws behind a single-molecule magnet behaviour, the mechanisms of magnetic relaxation that determines the magnetic properties and the relationship of these properties with the structure of single-molecule magnets. This review focuses on the physical methods providing such understanding, including different versions and various combinations of magnetometry, electron paramagnetic and nuclear magnetic resonance spectroscopy, optical spectroscopy and X-ray diffraction. Many of these methods are traditionally used to determine the composition and structure of new chemical compounds. However, they are rarely applied to study molecular magnetism.

The bibliography includes 224 references.

Syntheses, structural modulation, and slow magnetic relaxation of three dysprosium(III) complexes with mononuclear, dinuclear, and one-dimensional structures

Three mononuclear, dinuclear and one-dimensional dysprosium(III) complexes based on 3-azotriazolyl-2,6-dihydroxybenzoic acid (H₄ATB) of [Dy(H₃ATB)₃]·3H₂O (1), [Dy₂(H₂ATB)₂(H₂DHB)₂(H₂O)₄]·2CH₃CN·5H₂O (2), and [Dy₂(H₂ATB)₂(DCB)(DMF)₂(H₂O)₂]·4DMF (3) were synthesized and structurally characterized by X-ray single crystal diffraction (H₃DHB = 2,6-dihydroxybenzoic acid, H₂DCB = 1,4-dicarboxybenzene). Complex 1 was used as a precursor to synthesize complexes 2 and 3, and 2 was further used to synthesize 3. Complex 1 is a mononuclear complex, in which the Dy(III) ion is in a nine-coordinated structure surrounded by three tridentate chelate H₃ATB^- ligands. Complex 2 displays a dinuclear structure bridged by two μ₂ carboxyl groups of two H₂DHB^- ligands and two μ_1,1-O atoms from the phenolic hydroxyl groups of two H₂ATB^2- ligands. Complex 3 shows a one-dimensional structure formed by two bridging DCB^2- ligands. The magnetic measurements were performed on three complexes 1-3, and they showed different magnetic behavior. Complex 1 shows a field-induced slow magnetic relaxation. Complexes 2 and 3 display distinct slow magnetic relaxation under zero dc field with energy barriers (U_eff) of 26(2) cm^-1 and 11(1) cm^-1, respectively. The magnetic behavior of three complexes 1-3 was investigated by ab initio calculations.

Polymeric Terbium(III) Squarate Hydrate as a Luminescent Magnet

Polymeric terbium(III) squarate hydrate [{Tb2(C4O4)3(H2O)8}n] was prepared from TbCl3 or Tb2O3 and squaric acid. The crystal structure was determined in a monoclinic Pc space group, and the whole molecular arrangement gives a sandwiched two-dimensional structure. The coordination polyhedra are described as a square antiprism. The solid complex emits green light under UV irradiation at room temperature with the quantum yield of 25%. Although Tb3+ is a non-Kramers ion, the alternating-current magnetic susceptibility showed frequency dependence in a 2000-Oe DC field, and the effective energy barrier for magnetization reorientation was 33(2) K. Thus, [{Tb2(C4O4)3(H2O)8}n] displayed functions of a potential luminescent magnet.