Mononuclear Lanthanide Complexes Research Articles

Toward Magneto-Optical Cryogenic Thermometers with High Sensitivity: A Magnetic Circular Dichroism Based Thermometric Approach.

Remote temperature probing at the cryogenic range is of utmost importance for the advancement of future quantum technologies. Despite the notable achievements in luminescent thermometers, accurately measuring temperatures below 10 K remains a challenging endeavor. In this study, we propose a novel magneto-optical thermometric approach based on the magnetic-circular dichroism (MCD) technique, which offers unprecedented capabilities for meticulous temperature variation analysis at cryogenic temperatures. The inherent temperature sensitivity of the MCD C-term, in conjunction with both positive and negative signals, enables highly sensitive magneto-optical temperature probing. Additionally, a groundbreaking relative thermal sensitivity value of 95.3 % K-1 at 2.54 K can be achieved using a mononuclear lanthanide complex, [[Ho(acac)3 (phen)], in the presence of a 0.25 T applied magnetic field and using a combination of multiparametric thermal read-out with multiple regression. These results unequivocally demonstrate the viability and effectiveness of our methodology for cryogenic temperature sensing.

Toward Magneto‐Optical Cryogenic Thermometers with High Sensitivity: A Magnetic Circular Dichroism Based Thermometric Approach

AbstractRemote temperature probing at the cryogenic range is of utmost importance for the advancement of future quantum technologies. Despite the notable achievements in luminescent thermometers, accurately measuring temperatures below 10 K remains a challenging endeavor. In this study, we propose a novel magneto‐optical thermometric approach based on the magnetic‐circular dichroism (MCD) technique, which offers unprecedented capabilities for meticulous temperature variation analysis at cryogenic temperatures. The inherent temperature sensitivity of the MCD C‐term, in conjunction with both positive and negative signals, enables highly sensitive magneto‐optical temperature probing. Additionally, a groundbreaking relative thermal sensitivity value of 95.3 % K−1 at 2.54 K can be achieved using a mononuclear lanthanide complex, [[Ho(acac)3(phen)], in the presence of a 0.25 T applied magnetic field and using a combination of multiparametric thermal read‐out with multiple regression. These results unequivocally demonstrate the viability and effectiveness of our methodology for cryogenic temperature sensing.

Cooperative Sensitization Upconversion in Solution Dispersions of Co‐Crystal Assemblies of Mononuclear Yb3+ and Eu3+ Complexes

AbstractLanthanide upconversion luminescence in nanoparticles has prompted continuous breakthroughs in information storage, temperature sensing, and biomedical applications, among others. Achieving upconversion luminescence at the molecular scale is still a critical challenge in modern chemistry. In this work, we explored the upconversion luminescence of solution dispersions of co‐crystals composed of discrete mononuclear Yb(DBM)3Bpy and Eu(DBM)3Bpy complexes (DBM: dibenzoylmethane, Bpy: 2,2′‐bipyridine). The 613 nm emission of Eu3+ was observed under excitation of Yb3+ at 980 nm. From the series of molecular assemblies studied, the most intense luminescence was obtained for a 1 : 1 molar ratio of Yb3+ : Eu3+, resulting in a high quantum yield of 0.67 % at 2.1 W cm−2. The structure and energy transfer mechanism of the assemblies were fully characterized. This is the first example of an Eu3+‐based upconverting system composed of two discrete mononuclear lanthanide complexes present as co‐crystals in non‐deuterated solution.

Cooperative Sensitization Upconversion in Solution Dispersions of Co-Crystal Assemblies of Mononuclear Yb3+ and Eu3+ Complexes.

Lanthanide upconversion luminescence in nanoparticles has prompted continuous breakthroughs in information storage, temperature sensing, and biomedical applications, among others. Achieving upconversion luminescence at the molecular scale is still a critical challenge in modern chemistry. In this work, we explored the upconversion luminescence of solution dispersions of co-crystals composed of discrete mononuclear Yb(DBM)3 Bpy and Eu(DBM)3 Bpy complexes (DBM: dibenzoylmethane, Bpy: 2,2'-bipyridine). The 613 nm emission of Eu3+ was observed under excitation of Yb3+ at 980 nm. From the series of molecular assemblies studied, the most intense luminescence was obtained for a 1 : 1 molar ratio of Yb3+  : Eu3+ , resulting in a high quantum yield of 0.67 % at 2.1 W cm-2 . The structure and energy transfer mechanism of the assemblies were fully characterized. This is the first example of an Eu3+ -based upconverting system composed of two discrete mononuclear lanthanide complexes present as co-crystals in non-deuterated solution.

Ab Initio Investigation of the Na3[Ln(ODA)3]·2NaClO4·6H2O (Ln = Ce-Yb; ODA = Oxydiacetate) Series.

In this work, the Na3[Ln(ODA)3]·2NaClO4·6H2O (Ln = Ce-Yb; ODA = oxydiacetate) series was analyzed with the ab initio ligand field theory (AILFT) module of the ORCA computational suite. The results were discussed within the framework of the angular overlap model (AOM) and compared to literature data. We find that the structural changes observed across the series exemplifies the effects of the lanthanide contraction also manifesting in the value of the AOM parameters. It is also shown that the complete active space self-consistent field (CASSCF) methodology is sufficient to describe the ligand field interactions in mononuclear lanthanide complexes, and the effects of dynamic correlation, through n-electron valence state perturbation theory (NEVPT2), are discussed. The calculated ligand field parameters of the present work are compared to the experimentally derived values from the literature.

Synthesis and characterization of some Lanthanide (III) Complexes based on 2, 6-Diphenylisonicotinic acid

This paper presents the synthesis of four mononuclear lanthanide (III) complexes, possessing 2, 6-Diphenylisonicotinate as a ligand.The complexes were synthesized in aqueous solution at room temperature in a one to three molar ratios of the Ln (III) salt and the ligand, respectively.The white or grayish powdered complexes that formed were characterized by elemental analysis, ftir, uv, and Fluorescence spectroscopy. The ftir absorption spectra indicated that 2, 6-Diphenylisonicotinate acts as a bidentate ligand and coordinates to Ln (III) through the carboxylate oxygen and the adjacent carbonyl oxygen (–C=O).The UV absorption spectra of the complexes are similar in band profile and shape to the spectrum of the ligand except a slight blue shift of the absorption maxima. The excitation and emission spectra of the complexes are very much similar to that of the ligand with minor differences in excitation and emission wavelengths.The elemental analysis results show a good agreement between the calculated and found percentages of chn. Based on the elemental analysis andspectroscopic resultsof the four complexes, wesuggestthat the compounds formed are nine coordinate around the metal center and have the general formulaLn(C18H12NO2)3.3H2O.

Circularly polarized luminescence of lanthanide complexes: From isolated individuals, discrete oligomers, to hierarchical assemblies

AbstractCircularly polarized luminescence (CPL) is the emission featured spatial orientation equivalent to circular dichroism. Owning to the unique magnetic dipole‐allowed but electric‐dipole‐forbidden 4f→ 4ftransitions, chiral lanthanide complexes have been recognized as ideal candidates to achieve unprecedented luminescence dissymmetry factor (glum). Their inherent electric‐dipole‐forbidden transition can be partly allowed, through the rational design of coordination ligands to lower the surrounding symmetry, further endowing them with relatively high quantum yields (QYs). Moreover, the blossom of supramolecular chemistry in lanthanide complexes allows for the construction of discrete oligomers and hierarchical assemblies, rendering them with enhanced chiroptical activities. Here, we deploy this review by summarizing recent advances in the chiroptical properties of lanthanide complexes, spanning multiple scales from isolated mononuclear individuals, discrete polynuclear oligomers, to infinite hierarchical assemblies. We first introduce the basic concept and several important parameters for the assessment of CPL activity. Then, isolated mononuclear lanthanide complexes coordinated with different types of antennas, along with the unique chirality transfer and induction in achiral lanthanide complexes were discussed. Next, the systematical discussion on chiroptical properties in discrete polynuclear lanthanide oligomers and infinite hierarchical lanthanide assemblies was presented. Meanwhile, the state‐of‐the‐art applications of CPL‐active lanthanide complexes were revisited. We end up this review with the conclusion and prospects, involving the rational design of ligands, directed and hierarchically precise self‐assembly, and extending applications of chiral lanthanide complexes.image

Halogen Bond Mediated Self-Assembly of Mononuclear Lanthanide Complexes: Perception of Supramolecular Interactions, Slow Magnetic Relaxation, and Photoluminescence Properties.

Five new mononuclear lanthanide complexes, [LnL2][Et3NH]·THF/H2O (Ln = Nd, Tb, Dy) (H2LCl = 2-bis(2-hydroxy-3,5-dichloro benzyl)aminomethyl]pyridine), Ln = Nd (1), Tb (2), and Dy (3), and (H2LBr = 2-bis(2-hydroxy-3,5-dibromo benzyl)aminomethyl]pyridine), Ln = Nd (4, H2O) and Tb (5), were synthesized and structurally characterized by single-crystal X-ray diffraction analyses. Being isostructural in all the five cases, the metal center is octa-coordinated with a triangular dodecahedron (D2d symmetry) geometry, and it is independent of the halogen substitution (Cl/Br). This close similarity is due to the composite interplay of hydrogen/halogen bond interactions that control the overall crystal packing, yet notable differences in association patterns among the individual ones arise from the subtle stereo-electronic requirement of individual molecules in the three-dimensional (3D) architecture. Hirshfeld surface and density functional theory (DFT) calculations clearly vouch for the importance of the hydrogen bond and halogen bond interactions observed in the structure. Detailed magnetic measurements using direct-current and alternating-current susceptibility measurements show slow magnetic relaxation in 3, a characteristic feature of the single-molecule magnets (SMMs), which is not shown by 1 and 2. Steady-state and time-resolved photoluminescence of Tb(III) complexes shows a strong ligand-to-metal energy transfer that can be modulated by changing the substitution on phenolic ligands. The results from these analyses indicate that it may be advantageous to consider the subtle role of hydrogen bond (HB)/halogen bond (XB) intermolecular interactions judiciously for the design of SMMs and luminescent materials based on halogen-substituted ligands.

Lanthanide SMMs Based on Belt Macrocycles: Recent Advances and General Trends.

Enhancement of axial magnetic anisotropy is the central objective to push forward the performance of Single-Molecule Magnet (SMM) complexes. In the case of mononuclear lanthanide complexes, the chemical environment around the paramagnetic ion must be tuned to place strongly interacting ligands along either the axial positions or the equatorial plane, depending on the oblate or prolate preference of the selected lanthanide. One classical strategy to achieve a precise chemical environment for a metal centre is using highly structured, chelating ligands. A natural approach for axial-equatorial control is the employment of macrocycles acting in a belt conformation, providing the equatorial coordination environment, and leaving room for axial ligands. In this review, we present a survey of SMMs based on the macrocycle belt motif. Literature systems are divided in three families (crown ether, Schiff-base and metallacrown) and their general properties in terms of structural stability and SMM performance are briefly discussed.

Salen-type mononuclear dysprosium complex displays significant single-molecule magnet performance

The newly isolated salen-type mononuclear lanthanide complex [Dy(5-NO2salcy)(NO3)(CH3OH)2] (1) reveals a uniquely high energy barrier of 64.94 K under zero dc field and a remarkable hysteresis loop at 6 K compared with known salen-type Dy-SIMs.

Crystal structure, magnetic properties and luminescent behavior of four mononuclear lanthanide-radical complexes

Four mononuclear lanthanide complexes based on a long nitronly nitroxide radical NIT-PhOPyrim, [Ln(hfac)3(NIT-PhOPyrim)(H2O)] (Ln(Ⅲ) = Gd 1, Tb 2, Dy 3, Er4; hfac = hexafluoroacetylacetonate; NIT-PhOPyrim = 2-[4-(pyrimidin-2-yloxy)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been synthesized and characterized. Single crystal X-ray diffraction analyses revealed that these four complexes are isomorphic in which each Ln(Ⅲ) ion is eight-coordinated by six oxygen atoms from three hfac ligands, one oxygen atom from one water molecule and one oxygen atom from the NO group of NIT-PhOPyrim ligand. Particularly, the coordinated water molecules were connected other mononuclear units through their hydrogen bonds into tetra-nuclear complexes and/or dimers. Variable temperature magnetization of complex 1 was shown the ferromagnetic interaction between Gd(III) ion and nitroxide radical, while weak intermolecular antiferromagnetic interactions through hydrogen bonds. Alternating-current (ac) magnetic susceptibility of complexes 2–4 revealed no magnetic relaxation behavior. Furthermore, Tb complex can detect Fe3+anion with a high sensitivity and selectivity through the fluorescence quenching effect.

Novel Lanthanide (III) Complexes Derived from an Imidazole–Biphenyl–Carboxylate Ligand: Synthesis, Structure and Luminescence Properties

A series of neutral mononuclear lanthanide complexes [Ln(HL)2(NO3)3] (Ln = La, Ce, Nd, Eu, Gd, Dy, Ho) with rigid bidentate ligand, HL (4′-(1H-imidazol-1-yl)biphenyl-4-carboxylic acid) were synthesized under solvothermal conditions. The coordination compounds have been characterized by infrared spectroscopy, thermogravimetry, powder X-ray diffraction and elemental analysis. According to X-ray diffraction, all the complexes are a series of isostructural compounds crystallized in the P2/n monoclinic space group. Additionally, solid-state luminescence measurements of all complexes show that [Eu(HL)2(NO3)3] complex displays the characteristic emission peaks of Eu(III) ion at 593, 597, 615, and 651 nm.

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes.

The reaction of fluoride anions with mononuclear lanthanide(III) and yttrium(III) hexaaza-macrocyclic complexes results in the formation of dinuclear fluoride-bridged complexes. As indicated by X-ray crystal structures, in these complexes two metal ions bound by the macrocycles are linked by two or three bridging fluoride anions, depending on the type of the macrocycle. In the case of the chiral hexaaza-macrocycle L1 derived from trans-1,2-diaminocyclohexane, the formation of these μ2-fluorido dinuclear complexes is accompanied by enantiomeric self-recognition of macrocyclic units. In contrast, this kind of recognition is not observed in the case of complexes of the chiral macrocycle L2 derived from 1,2-diphenylethylenediamine. The reaction of fluoride with a mixture of mononuclear complexes of L1 and L2, containing two different Ln(III) ions, results in narcissistic sorting of macrocyclic units. Conversely, a similar reaction involving mononuclear complexes of L1 and complexes of achiral macrocycle L3 based on ethylenediamine results in sociable sorting of macrocyclic units and preferable formation of heterodinuclear complexes. In addition, formation of these heterodinuclear complexes is accompanied by chirality transfer from the chiral macrocycle L1 to the achiral macrocycle L3 as indicated by CPL and CD spectra.

Field-Induced SMM and Vis/NIR Luminescence on Mononuclear Lanthanide Complexes with 9-Anthracenecarboxylate and 2,2′:6,2″-Terpyridine

Five new mononuclear lanthanide complexes are synthesized by adding the several lanthanide nitrate hexahydrate salts, which for lanthanide (Ln) are Eu, Tb, Dy, Er, and Yb, with 9-anthracenecarboxylic acid (9-Hanthc) and 2,2′:6,2″-terpyridine (TPY) in mixed solution of methanol and dimethylformamide (DMF). The general formula is [Eu(9-anthc)3(TPY)(DMF)]·H2O (1Eu) where Eu(III) is ennea-coordinated or [Ln(9-anthc)3(TPY)(H2O)]·H2O·DMF (Ln = Tb (2Tb), Dy (3Dy), Er (4Er), and Yb (5Yb)) where Ln(III) is octa-coordinated. For compounds 3Dy, 4Er, and 5Yb, the dynamic ac magnetic study indicated field-induced single molecule magnet (SMM) behavior. The photoluminescence studies in the solid state of these complexes show the sensitization of 4f-4f transitions for 4Er and 5Yb in the NIR region.

Frontispiece: Mononuclear Dysprosium Alkoxide and Aryloxide Single‐Molecule Magnets

Mononuclear lanthanide (Ln) complexes can be high-performing single-molecule magnets (SMMs). Recently, there has been an influx of mononuclear Ln alkoxide and aryloxide SMMs. Here, mononuclear DyIII alkoxide and aryloxide SMMs with coordination numbers up to eight are covered in detail, with additional brief overviews of TbIII, HoIII, ErIII and YbIII SMMs. For more information, see the review by V. S. Parmar, D. P. Mills and R. E. P. Winpenny on page 7625 ff.

Synthesis of Novel Mononuclear Lanthanide (Ln3+) Complexes with Indole-3-acetic Acid Hormone, Their Structure and Properties Based on Spectroscopic and In Silico Studies

Synthesis of Novel Mononuclear Lanthanide (Ln3+) Complexes with Indole-3-acetic Acid Hormone, Their Structure and Properties Based on Spectroscopic and In Silico Studies

Syntheses, structures and magnetic properties of a series of lanthanide complexes with reduced nitronyl nitroxide radical ligands

A series of new lanthanide complexes [Ln(hfac)3](HIM-6-X-Py)2 [HIM-6-X-Py = 2-(6-X-2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide; hfac = hexafluoroacetylacetonate; X = Br, Ln = Tb (Br-Tb), Dy (Br-Dy), Ho (Br-Ho), Er (Br-Er), Yb (Br-Yb); X = Cl, Ln = Dy (Cl-Dy); X = F, Ln = Dy (F-Dy)] have been prepared and studied. During the preparation of the lanthanide complexes, the nitronyl nitroxide radical ligands NIT-6-X-Py (2-(6-X-2-pyridyl)-4,4,5,5-tetramethylimidazolyl-1-oxyl-3-oxide; X = F, Cl, Br) were reduced to the non-radical ligands HIM-6-X-Py, forming mononuclear lanthanide complexes with two HIM-6-X-Py ligands chelated to one lanthanide(III) ion. The reduced ligands were evidenced by the color of the lanthanide complexes, the characteristic IR band of N–H stretching absorption, the residue electron density near the N atom of the ligand, and the N–O bond lengths in the final metal complexes. Except for compound F-Dy which crystallized in the triclinic space group P1¯ with two isolated DyIII centers in an asymmetricunit, all other complexes crystallized in the monoclinic space group P21/n. Due to the reduced non-radical ligands, the magnetic properties of all these complexes are consistent with mononuclear LnIII compounds. Alternating-current (ac) magnetic susceptibility investigations revealed that complexes Br-Dy, Br-Er, Br-Yb, Cl-Dy and F-Dy exhibit field-induced frequency dependence which indicates the slow magnetic relaxation of these complexes.

Exploiting complementary ligands for the construction of square antiprismatic monometallic lanthanide SMMs.

The methylation of p-tert-butylcalix[4]arene in the distal 1,3-phenolic sites provides the ligand H2L = {p-tert-butylcalix[4](OMe)2(OH)2arene} that enables construction of heteroleptic mononuclear lanthanide complexes. The reaction of (N(nBu)4)(acac) (Hacac = acetylacetone), MIIICl3 and H2L under Schlenk conditions results in the formation of a family of (N(nBu)4)[MIIIL(acac)2] complexes where M = Y (1), Gd (2), Tb (3) and Dy (4). The metal ions are eight-coordinate in distorted square-antiprismatic coordination geometries, resulting in slow relaxation of the magnetisation for the Tb derivative.

Structural and magnetic studies of mononuclear lanthanide complexes derived from N-rich chiral Schiff bases

A new family of mononuclear lanthanide complexes with the formula [CeIII(L)(NO3)3(MeOH)] (1) and [LnIII(L)(NO3)3]·MeOH where Ln = Gd (2) or Dy (3) and L = N,N'-bis(pyridin-2-ylmethylene)cyclohexane-1,2-diamine has been obtained with the use of enantiomerically pure Schiff bases. Dynamic magnetic studies indicate that 1-3 present field-induced slow relaxation of the magnetization and their response has been compared with the magnetically diluted complexes 2d and 3d. Structural studies have been carried out by single crystal X-ray and powder diffraction.

Synthesis, structures, and one- or two-electron reduction reactivity of mononuclear lanthanide (Ho, Dy) complexes with sterically hindered o-iminobenzoquinone ligands

Complexes of Dy and Ho (Ln) with redox-active 4,6-di-t-butyl-N-(2,6-di-isopropylphenyl)-o-iminobenzoquinone ligand (dippIQ) in different charged states have been synthesized and investigated. Besides the neutral state, the ligand is comprised as iminosemiquinolate (dippISQ–) or amidophenolate (dippAP2–). Homoligand complexes [Ln(dippIQ)2I3] (1Ln), [Ln(dippISQ)2I(thf)2] (2Ln, thf = tetrahydrofurane) and [KLn(dippAP)2(thf)4] (3Ln) have been obtained by earlier known methods that include complexation (for 1Ln) followed by reduction with 2 or 4 equivalents of KC8 (for 2Ln and 3Ln, respectively). It has been shown that upon reduction by 3 equivalents of KC8 mixed-ligand complexes [Ln(dippAP)(dippISQ)(thf)2] (4Ln) are formed. Simple synthetic methods to the high-yield syntheses of 3Ln and 4Ln have been developed, based on excessive reduction by K metal (for the former complex), followed by partial oxidation by I2 (for the latter one). In addition to the known reactivity of 3Ln towards S8 as a 2e reductant, 4Ln was shown to act as 1e reductants, according to the number of reducing dippAP2– ligands. The reduction by 3Ln results in inclusion of S52– anion in the coordination sphere, resulting in the known type [Ln(dippISQ)2(S5)]– complexes, crystallized with the [K(18-Crown-6)(thf)2]+ cation (6Ln). Unlike that, the reduction by 4Ln results in inclusion of a chain of two sulfur atoms with the formation of new type of ligand (dippAP)S22– in a complex [Ln(dippISQ){(dippAP)S2}(thf)2] (7Ln). Structures of all complexes are compared on the basis of X-ray diffraction and IR spectroscopy data. Reaction routes leading to the complexes of different types are discussed.