Dinuclear enantiopure Ln3+ complexes with (S-) and (R-) 2-phenylbutyrate ligands. Luminescence, CPL and magnetic properties

The reaction of Ln(NO3)2·6H2O (Ln = Nd, Sm, Eu, Tb, Dy, Tm and Yb) with the respective enantiopure (R)-(-)-2-phenylbutyric or (S)-(+)-2-phenylbutyric acid (R/S-2-HPhBut) and 4,7-diphenyl-1,10-phenanthroline (Bphen) allows the isolation of chiral dinuclear compounds of the formula [Ln2(μ-R/S-2-PhBut)4(R/S-2PhBut)2(Bphen)2] where Ln = Nd3+ (R/S-Nd-a), Sm3+ (R/S-Sm-a), Eu3+ (R/S-Eu-a), Tb3+ (R/S-Tb-a and R/S-Tb-b), Dy3+ (R/S-Dy-a and R/S-Dy-b), Tm3+ (R/S-Tm-b) and Yb3+ (R/S-Yb-b). Single crystal X-ray diffraction was performed for compounds S-Eu-a and S-Tm-b. Powder crystal X-ray diffraction was performed for all complexes. From the crystallographic data two different structural motifs were found which are referred to as structure type a and structure type b. In structure type a, the Ln3+ atoms are bridged through four R or S-2-PhBut ligands with two different kinds of coordination modes whereas in structure type b the two Ln3+ atoms are bridged through four R or S-2-PhBut ligands showing only one kind of coordination mode. For those lanthanide ions exhibiting both structure types, Tb3+ and Dy3+, a difference in the luminescence and magnetism behavior is observed. All compounds (except R/S-Tm-b) exhibit sensitized luminescence, notably the Eu3+ and Tb3+ analogues. Circular Dichroism (CD) and Circular Polarized Luminescence (CPL) in the solid state and in 1 mM dichloromethane (DCM) solutions are reported, leading to improved chiroptical properties for the DCM solutions. The asymmetry factor (glum) in 1 mM DCM is ±0.02 (+ for R-Eu-a) for the magnetically allowed transition 5D0 → 7F1 and ±0.03 (+ for R-Tb-a and R-Tb-b) for the 5D4 → 7F5 transition. Magnetic properties of all compounds were studied and the Dy3+ compound with the structural motif b (R-Dy-b) shows Single Molecular Magnet (SMM) behavior under a 0 T magnetic field. However, R-Dy-a is a field-induced SMM.

Magneto-structural correlation in lanthanide luminescent [2.2]paracyclophane-based single-molecule magnets

The association of lanthanide ions and paracyclophane derivatives has been very scarcely reported in the literature. In this study, elaboration of five coordination lanthanide complexes involving the 1,4(1,4)-dibenzenacyclohexaphane-12,43-diylbis(diphenylphosphine oxide) ligand (L) was achieved with the determination of single-crystal X-ray diffraction structures of four mononuclear complexes of formula [Ln(hfac)3(L)] (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate) (Ln = Dy(III) (1-Dy) and Yb(III) (2-Yb)) and [Ln(tta)3(L)] (tta- = 2-tenoyl-trifluoroacetylacetonate) (Ln = Dy(III) (3-Dy) and Yb(III) (4-Yb)) and one dinuclear complex [Na(Dy2(hfac)6(L)2)](BArF) (BArF- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) (5-Dy). The compounds were characterized using elemental analysis, IR spectroscopy, DC and AC magnetic measurements and photophysical investigations. L is an efficient organic chromophore for the sensitization of both visible Dy(III) (1-Dy) and near-infrared Yb(III) (2-Yb and 4-Yb) luminescence. The combination of excitation and emission spectra allowed the determination of the crystal field spitting of both the 2F7/2 ground state and 2F5/2 excited state for 2-Yb and 4-Yb. Moreover, 3-Dy and the two Yb(III) derivatives displayed field-induced single-molecule magnet (SMM) behaviour with slow magnetic relaxation occurring through the Raman process only for 2-Yb and 4-Yb, whereas a combination of Orbach and Raman processes was identified for 3-Dy.

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.

Circularly polarized luminescence in the one-dimensional assembly of binaphtyl-based Yb(iii) single-molecule magnets

Lanthanide ions have attracted great interest owing to their optical and magnetic properties. Single-molecule magnet (SMM) behavior has been a fascinating science for thirty years. Moreover, chiral lanthanide complexes allow the observation of remarkable circularly polarized luminescence (CPL). However, the combination of both SMM and CPL behaviors in a single molecular system is very rare and deserves attention in the design of multifunctional materials. Four chiral one-dimensional coordination compounds involving 1,1'-Bi-2-naphtol (BINOL)-derived bisphosphate ligands and the Yb(iii) centre were synthesized and characterized by powder and single-crystal X-ray diffraction. All the Yb(iii)-based polymers displayed field-induced SMM behavior with magnetic relaxation occurring by applying Raman processes and near infrared CPL in the solid state.

Multifunctional Helicene-Based Ytterbium Coordination Polymer Displaying Circularly Polarized Luminescence, Slow Magnetic Relaxation and Room Temperature Magneto-Chiral Dichroism

The combination of physical properties sensitive to molecular chirality in a single system allows the observation of fascinating phenomena such as magneto-chiral dichroism (MChD) and circularly polarized luminescence (CPL) having potential applications for optical data readout and display technology. Homochiral monodimensional coordination polymers of Yb^III were designed from a 2,15-bis-ethynyl-hexahelicenic scaffold decorated with two terminal 4-pyridyl units. Thanks to the coordination of the chiral organic chromophore to Yb(hfac)₃ units (hfac^- =1,1,1,5,5,5-hexafluoroacetylaconate), efficient NIR-CPL activity is observed. Moreover, the specific crystal field around the Yb^III induces a strong magnetic anisotropy which leads to a single-molecule magnet (SMM) behaviour and a remarkable room temperature MChD. The MChD-structural correlation is supported by computational investigations.

Back to the future of organolanthanide chemistry

At the dawn of the development of structural organometallic chemistry, soon after the discovery of ferrocene, the description of the LnCp₃ complexes, featuring large and mostly trivalent lanthanide ions, was rather original and sparked curiosity. Yet, the interest in these new architectures rapidly dwindled due to the electrostatic nature of the bonding between π-aromatic ligands and 4f-elements. Almost 70 years later, it is interesting to focus on how the discipline has evolved in various directions with the reports of multiple catalytic reactivities, remarkable potential in small molecule activation, and the development of rich redox chemistry. Aside from chemical reactivity, a better understanding of their singular electronic nature - not precisely as simplistic as anticipated - has been crucial for developing tailored compounds with adapted magnetic anisotropy or high fluorescence properties that have witnessed significant popularity in recent years. Future developments shall greatly benefit from the detailed reactivity, structural and physical chemistry studies, particularly in photochemistry, electro- or photoelectrocatalysis of inert small molecules, and manipulating the spins' coherence in quantum technology.

Multifunctional Lanthanide-Based Metal-Organic Frameworks Derived from 3-Amino-4-hydroxybenzoate: Single-Molecule Magnet Behavior, Luminescent Properties for Thermometry, and CO2 Adsorptive Capacity

Herein, we describe and study a new family of isostructural multifunctional metal–organic frameworks (MOFs) with the formula {[Ln₅L₆(OH)₃(DMF)₃]·5H₂O}_n (where (H₂L) is 3-amino-4-hydroxybenzoic acid ligand) for magnetism and photoluminescence. Interestingly, three of the materials (Dy-, Er-, and Yb-based MOFs) present single-molecule magnet (SMM) behavior derived from the magnetic anisotropy of the lanthanide ions as a consequence of the adequate electronic distribution of the coordination environment. Additionally, photoluminescence properties of the ligand in combination with Eu and Tb counterparts were studied, including the heterometallic Eu–Tb mixed MOF that shows potential as ratiometric luminescent thermometers. Finally, the porous nature of the framework allowed showing the CO₂ sorption capacity.

A new family of isostructural multifunctional metal−organic frameworks has been described and studied for magnetism and photoluminescence. Interestingly, some materials present single-molecule magnet behavior, and photoluminescence properties of the ligand in combination with Eu and Tb counterparts were studied, including the heterometallic Eu−Tb mixed MOF that shows potential as ratiometric luminescent thermometers. Finally, the porous nature of the framework allowed showing the CO₂ sorption capacity.

Polarized Neutron Diffraction: An Excellent Tool to Evidence the Magnetic Anisotropy—Structural Relationships in Molecules

This publication reviews recent advances in polarized neutron diffraction (PND) studies of magnetic anisotropy in coordination compounds comprising d or f elements and having different nuclearities. All these studies illustrate the extent to which PND can provide precise and direct information on the relationship between molecular structure and the shape and axes of magnetic anisotropy of the individual metal sites. It makes this experimental technique (PND) an excellent tool to help in the design of molecular-based magnets and especially single-molecule magnets for which strong uniaxial magnetic anisotropy is required.

Magnetic anisotropies of Ho(III) and Dy(III) single-molecule magnets experimentally determined via polarized neutron diffraction

We present the magnetic anisotropy of two isostructural pentagonal-bipyramidal complexes, [Ln(H₂O)₅(HMPA)₂]I₃·2HMPA (HMPA = hexamethylphosphoramide, Ln = Dy, Ho). Using ac magnetic susceptibility measurements, we find magnetic relaxation barriers of 600 K and 270 K for the Dy- and Ho-compounds, respectively. This difference is supported by polarized neutron diffraction (PND) measured at 5 K and 1 T which provides the first experimental evidence that the transverse elements in the magnetic anisotropy of the Ho-analogue are significant, whereas the Dy-analogue has a near-axial magnetic anisotropy with vanishing transverse contributions. The coordination geometries of the two complexes are highly similar, and we attribute the loss of strong magnetic axiality as expressed in the atomic susceptibility tensors from PND, as well as the smaller relaxation barrier in the Ho-complex compared to the Dy-complex, to the less favorable interaction of the pentagonal bipyramidal crystal field with the characteristics of the Ho(III) 4f-charge distribution.

Structural Diversity of Lanthanide 3-Nitrotrispyrazolylborates: Tunable Nuclearity and Intra-Ligand Charge Transfer Sensitization of Visible and NIR Ln3+ Emission

Reported are the syntheses, crystal structures, and photophysical properties of 28, novel lanthanide compounds across five structural types, [Ln(3-NO₂Tp)₂(NO₃)] (1-Ln, Ln = La-Tm, except Pm), [Bu₄N][Ln(3-NO₂Tp)(NO₃)₃] (2-Ln, Ln = Yb, Lu), [Eu(3-NO₂Tp)₂Cl(H₂O)]·2ⁱPrOH (3-Eu), [{Ln(3-NO₂Tp)₂}₂(μ₂-CO₃)]·MeOH (4-Ln, Ln = La-Gd, except Pm), and [{Ln(3-NO₂Tp)}₄(μ₂-OMe)₆(μ₄-O)] (5-Ln, Ln = Pr-Tb, except Pm) with the 3-nitrotrispyrazolylborate (3-NO₂Tp^-) ligand. The reaction of methanol or isopropanol solutions of LnX₃ (X = Cl, NO₃) with the tetrabutyl ammonium salt of the flexidentate 3-NO₂Tp^- ([Bu₄N][3-NO₂Tp]) yields Ln(3-NO₂Tp)_x complexes of various nuclearities as either monomers (1-Ln, 2-Ln, 3-Eu), dimers (4-Ln), or tetramers (5-Ln) owing to the efficient conversion of atmospheric CO₂ to CO₃^2- (dimers) or ligand controlled solvolysis of lanthanide ions (tetramers). 3-NO₂Tp^- is an efficient sensitizer for both the visible and near-IR (NIR) emissions of most of the lanthanide series, except thulium. Optical measurements, supported by density functional theory calculations, indicate that the dual visible and NIR Ln³⁺ emission arises from two intraligand charge transfer (ILCT) transitions of 3-NO₂Tp^-. This is the first report of lanthanide complexes with a nitro-functionalized pyrazolylborate ligand. The derivatization of the known Tp^- ligand results in new coordination chemistry governed by the increased denticity of 3-NO₂Tp^-, imparting remarkable structural diversity and charge transfer properties to resultant lanthanide complexes.

Chiral or Luminescent Lanthanide Single-Molecule Magnets Involving Bridging Redox Active Triad Ligand

The reactions between the bis(1,10-phenantro[5,6-b])tetrathiafulvalene triad (L) and the metallo-precursors Yb(hfac)3(H2O)2 (hfac− = 1,1,1,5,5,5-hexafluoroacetylacetonato anion) and Dy(facam)3 (facam− = 3-trifluoro-acetyl-(+)-camphorato anion) lead to the formation of two dinuclear complexes of formula [Yb2(hfac)6(L)]·2(C7H16) ((1)·2(C7H16)) and [Dy2((+)facam)6(L)]·2(C6H14) ((2)·2(C6H14)). The X-ray structures reveal that the L triad bridges two terminal Yb(hfac)3 or Dy(facam)3 units. (1)·2(C7H16) behaved as a near infrared YbIII centered emitter and a field-induced Single-Molecule Magnet (SMM) while (2)·2(C6H14) displayed SMM behavior in both zero- and in-dc field. The magnetization mainly relaxes through a Raman process for both complexes under an optimal applied magnetic field.

Single-Ion Anisotropy and Intramolecular Interactions in CeIII and NdIII Dimers

This article reports the syntheses, characterization, structural description, together with magnetic and spectroscopic properties of two isostructural molecular magnets based on the chiral ligand N,N'-bis((1,2-diphenyl-(pyridine-2-yl)methylene)-(R,R/S,S)-ethane-1,2-diamine), L1, of general formula [Ln2(RR-L1)2(Cl6)]·MeOH·1.5H2O, (Ln = Ce (1) or Nd (2)). Multifrequency electron paramagnetic resonance (EPR), cantilever torque magnetometry (CTM) measurements, and ab initio calculations allowed us to determine single-ion magnetic anisotropy and intramolecular magnetic interactions in both compounds, evidencing a more important role of the anisotropic exchange for the NdIII derivative. The comparison of experimental and theoretical data indicates that, in the case of largely rhombic lanthanide ions, ab initio calculations can fail in determining the orientation of the weakest components, while being reliable in determining their principal values. However, they remain of paramount importance to set the analysis of EPR and CTM on sound basis, thus obtaining a very precise picture of the magnetic interactions in these systems. Finally, the electronic structure of the two complexes, as obtained by this approach, is consistent with the absence of zero-field slow relaxation observed in ac susceptibility.

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.

Strong Equatorial Crystal Field Enhances the Axial Anisotropy and Energy Barrier for Spin Reversal Process in Yb2 Single Molecule Magnets

The importance of equatorial crystal fields on magnetic anisotropy of ytterbium single molecule magnets (SMMs) is observed for the first time. Herein, we report three similar dinuclear ytterbium complexes with the formula [Yb₂ (3-OMe-L)₂ (DMF)₂ (NO₃ )₂ ]⋅DMF (1), [Yb₂ (3-H-L)₂ (DMF)₂ (NO₃ )₂ ]⋅DMF⋅H₂ O (2), and [Yb₂ (3-NO₃ -L)₂ (DMF)₂ (NO₃ )₂ ] (3), [where 3-X-H₂ L=N'-(2-hydroxy-3-X-benzylidene)picolinohydrazide, X=OMe (1), H (2) NO₂ (3)]. Detailed magnetic measurements reveal the presence of weak antiferromagnetic interactions between the Yb centers and a field-induced slow relaxation of magnetization in all complexes. A higher energy barrier for spin reversal was observed for complex 1 (U_eff =50 K) and it decreases in the order of 2 (47 K) to 3 (40 K). Notably, complex 1 shows a remarkable energy barrier within the frequency range of 1-850 Hz reported for Yb-based SMMs. Further, ab initio calculations show a higher axial anisotropy and lower quantum tunneling of magnetization (QTM) in the ground state for 1 compared to 2 and 3. It was also observed that the presence of a strong crystal field in the equatorial plane (when the ∡ O1-Yb-O3 bond angle is close to 90°) enhances the axial anisotropy and improves the SMM behavior in the studied complexes. Both the experimental and theoretical analysis of relaxation dynamics discloses that Raman and QTM play major role on slow relaxation process for all complexes. To provide more insight into the exchange interactions, broken-symmetry DFT calculations were performed.

Asymmetric Ring Opening in a Tetrazine-Based Ligand Affords a Tetranuclear Opto-Magnetic Ytterbium Complex

We report the formation of a tetranuclear lanthanide cluster, [Yb₄ (bpzch)₂ (fod)₁₀ ] (1), which occurs from a serendipitous ring opening of the functionalised tetrazine bridging ligand, bpztz (3,6-dipyrazin-2-yl-1,2,4,5-tetrazine) upon reacting with Yb(fod)₃ (fod^- =6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octandionate). Compound 1 was structurally elucidated via single-crystal X-ray crystallography and subsequently magnetically and spectroscopically characterised to analyse its magnetisation dynamics and its luminescence behaviour. Computational studies validate the observed M_J energy levels attained by spectroscopy and provides a clearer picture of the slow relaxation of the magnetisation dynamics and relaxation pathways. These studies demonstrate that 1 acts as a single-molecule magnet (SMM) under an applied magnetic field in which the relaxation occurs via a combination of Raman, direct, and quantum tunnelling processes, a behaviour further rationalised analysing the luminescent properties. This marks the first lanthanide-containing molecule that forms by means of an asymmetric tetrazine decomposition.

Luminescence, chiroptical, magnetic and ab initio crystal-field characterizations of an enantiopure helicoidal Yb(iii) complex

The electronic structure of a chiral Yb(iii)-based complex is fully determined by taking advantage of experimental magnetic, luminescence, and chiroptical (NIR-ECD and CPL) characterizations in combination with ab initio wavefunction calculations.

Structural and spectroscopic investigations of nine-coordinate redox active lanthanide complexes with a pincer O,N,O ligand

The lanthanide complexes EuL3, GdL3, YbL3 and LuL3 of the N,N'-bis(2-hydroxy-di-3,5-tert-butylphenyl)amine were prepared. The X-Ray crystal structures of GdL3 and LuL3 demonstrated a nine-coordinate sphere with three ligand molecules under their anionic diamagnetic form (Cat-N-BQ)-. The complexes showed three oxidation events (Eox11/2 = 0.15-0.16 V, E1/22 = 0.51-55 V, and E1/23 = 0.75-0.78 V vs. Fc+/Fc) via cyclic voltammetry, corresponding to the successive oxidation of the aminophenolate moeities to iminosemiquinone species. The complexes GdL3 and YbL3 were characterized by EPR spectroscopy, allowing for the determination of the zero field splitting (ZFS) parameters in the first case. The monocations (LnL3)+ and monoanions (LnL3)- were electrochemically generated (Ln = Eu, Gd, Yb, Lu), as well as the dications YbL32+ and LuL32+. The spins are antiferromagnetically exchange coupled in the diradical species LuL32+ (|D| = 260 MHz, E = 0). All the complexes (incl. neutral) possess a strong absorption band in the NIR region (730-840 nm, ε > 19 mM-1 cm-1) corresponding to ligand-based transitions.

Structurally modulated single-ion magnets of mononuclear β-diketone dysprosium(iii) complexes

Four perturbed eight-coordinated mononuclear β-diketone based Dy(iii) SIMs with distinct hydrogen bond interactions and electron delocalization are noteworthily modulated by the aromatic groups of auxiliary ligands.

Coumarin-lanthanide based compounds with SMM behavior and high quantum yield luminescence

Coumarin-based lanthanide complexes of general formula [Ln(coum)3(phen)(H2O)x]·yH2O (Ln-phen, x = 0,1, 0 ≤ y ≤ 1.5; phen = 1,10-phenanthroline; coum = 3-acetyl-4-hydroxylato-coumarin; Ln = Eu, Tb, Dy, Tm) and [Ln(coum)3(batho)]·0.7EtOH (Ln-batho, batho = 4,7-diphenyl-1,10-phenanthroline; Ln = Eu, Tb, Dy, Tm) were synthesized. The magnetic relaxation and photoluminescence behavior of these complexes was compared with that of the related compounds [Ln(coum)3(EtOH)(H2O)]·EtOH (Ln-coum), so as to investigate the effects of incorporating a second chromophore, either the phen or batho ligand, to the original coordination scaffold, provided with three coumarin (coum) ligands. Slow relaxation of the magnetization under H = 0 with moderate activation energies was observed for the Dy-phen (U/kB = 99.1 K) and Dy-batho (U/kB = 67.1 K) compounds, whereas Tb analogues presented field-induced single molecule magnet (SMM) behavior, with U/kB = 11.7 K (16.6 K@3 kOe) for Tb-phen (Tb-batho), respectively. Luminescent emission in the visible range was observed for all the Ln-coumarin based compounds upon ligand sensitization, with high quantum yields of 45 (40%) for Eu-phen (Eu-batho) compounds and 65-76-58% for Tb-coum, phen, batho analogues. Sensitization is mainly provided by the coumarin ligand having the energy difference ΔE between its triplet state T1 and the lanthanide emitting level closest to the optimum, while the second ligand can play either a synergistic or competing sensitizing role. The Tb-phen/batho compounds presented simultaneously SMM and luminescent behavior, with excellent values of the bifunctional figure of merit (ηSMM-QY ∼ 1000% K). The reported compounds represent a new class of bifunctional materials with potential interesting application in various fields.

Understanding the near-infrared fluorescence and field-induced single-molecule-magnetic properties of dinuclear and one-dimensional-chain ytterbium complexes based on 2-hydroxy-3-methoxybenzoic acid

Two Yb(iii) complexes with a dinuclear and belt-like one-dimensional chain structure were reported. Their near-infrared luminescence and single-molecule magnetic properties were investigated in detail.