A new series of lanthanide-based complexes with a bis(hydroxy)benzoxaborolone ligand: synthesis, crystal structure, and magnetic and optical properties

Reactions, under hydrothermal conditions, between lanthanide chlorides and the sodium salt of 2-carboxyphenylboronic acid lead to a series of lanthanide-based complexes with general chemical formula [Ln₂(C₇H₅O₂)₄(C₇O₄H₆B)₂·4H₂O] with Ln = Eu–Dy.

Effect of magnetic anisotropy on direct chiral discrimination in paramagnetic NMR spectroscopy

We have studied the effect of thermally populated crystal field states on room temperature chiral discrimination in NMR spectroscopy.

Modulation of the properties of dinuclear lanthanide complexes through utilizing different β-diketonate co-ligands: near-infrared luminescence and magnetization dynamics

Four Dy₂ complexes based on the ligand H₂L display various slow magnetic relaxation behaviors through utilizing different β-diketonate co-ligands.

Covalency and magnetic anisotropy in lanthanide single molecule magnets: the DyDOTA archetype

Lanthanide ions when complexed by polyamino-polycarboxylate chelators form a class of compounds of paramount importance in several research and technological areas, particularly in the fields of magnetic resonance and molecular magnetism. Indeed, the gadolinium derivative is one of the most employed contrast agents for magnetic resonance imaging while the dysprosium one belongs to a new generation of contrast agents for T2-weighted MRI. In molecular magnetism, Single Molecule Magnets (SMMs) containing lanthanide ions have become readily popular in the chemistry and physics communities since record energy barriers to the reversal of magnetization were reported. The success of lanthanide complexes lies in their large anisotropy due to the contribution of the unquenched orbital angular momentum. However, only a few efforts have been made so far to understand how the f-orbitals can be influenced by the surrounding ligands. The outcomes have been rationalized using mere electrostatic perturbation models. In the archetype compound [Na{Dy(DOTA) (H2O)}]·4H2O (Na{DyDOTA}·4H2O) an unexpected easy axis of magnetization perpendicular to the pseudo-tetragonal axis of the molecule was found. Interestingly, a dependency of the orientation of the principal magnetization axis on the simple rotation of the coordinating apical water molecule (AWM) - highly relevant for MRI contrast - around the Dy-OAWM bond was predicted by ab initio calculations, too. However, such a behaviour has been contested in a subsequent paper justifying their conclusions on pure electrostatic assumptions. In this paper, we want to shed some light on the nature of the subtle effects induced by the water molecule on the magnetic properties of the DyDOTA archetype complex. Therefore, we have critically reviewed the structural models already published in the literature along with new ones, showing how the easy axis orientation can dangerously depend on the chosen model. The different computed behaviors of the orientation of the easy axis of magnetization have been rationalized as a function of the energy gap between the ground and the first excited doublet. Magneto-structural correlations together with a mapping of the electrostatic potential generated by the ligands around the Dy(iii) ion through a multipolar expansion have also been used to evidence and quantify the covalent contribution of the AWM orbitals.

A supramolecular chain of dimeric Dy single molecule magnets decorated with azobenzene ligands

Dy^III dimers decorated with photo-isomerizable azobenzene ligands behave as single-molecule magnets and self-organize into a supramolecular chain. Ab initio calculations, magnetic and optical properties are reported.

Enhancing the energy barrier of dysprosium(iii) single-molecule magnets by tuning the magnetic interactions through different N-oxide bridging ligands

The synergistic effect of strengthened Dy-Dy magnetic interactions and slightly enhanced symmetry of Dy^III ions results in a great U_eff enhancement from 11.79 K to 226.73 K.

Closing the Circle of the Lanthanide-Murexide Series: Single-Molecule Magnet Behavior and Near-Infrared Emission of the NdIII Derivative

Up to now, even if murexide-based complexometric studies are performed with all 3d or 4f ions, the crystal structures of the light-lanthanide derivatives of the lanthanide-murexide series are unknown. In this work, we report the crystal structure of the NdIII derivative named NdMurex. Contrary to all known complexes of the 3d or 4f series, a dimeric compound was obtained. As for its already reported DyIII and YbIII parents, the NdIII complex responsible for the color-change behaves as a single-molecule magnet (SMM). This behavior was observed on both the crystalline (NdMurex: Ueff = 6.20(0.80) K, 4.31 cm−1; τ0 = 2.20(0.92) × 10−5 s, Hdc = 1200 Oe) and anhydrous form (NdMurexAnhy: Ueff = 6.25(0.90) K, 4.34 cm−1; τ0 = 4.85(0.40) × 10−5 s, Hdc = 1200 Oe). The SMM behavior is reported also for the anhydrous CeIII derivative (CeMurexAnhy: Ueff = 5.40(0.75) K, 3.75 cm−1; τ0 = 3.02(1.10) × 10−5 s, Hdc = 400 Oe). The Near-Infrared Emission NIR emission was observed for NdMurexAnhy and highlights its bifunctionality.

Effect of Second-Order Spin-Orbit Coupling on the Interaction between Spin States in Spin-Crossover Systems

The second-order spin-orbit coupling is evaluated in two transition-metal complexes to establish the effect on the deactivation mechanism of the excited low-spin state in systems that undergo spin transitions under the influence of light. We compare the standard perturbational approach to calculate the second-order interaction with a variational strategy based on the effective Hamiltonian theory and show that the former one can only be applied in some special cases and even then gives results that largely overestimate the interaction. The combined effect of geometry distortions and second-order spin-orbit coupling leads to sizeable interactions for states that are nearly uncoupled in the symmetric (average) structure of the complex. This opens the possibility of a direct deactivation from the singlet and triplet states of the metal-to-ligand charge-transfer manifold to the final high-spin state as suggested from the interpretation of experimental data but so far not supported by theoretical descriptions of the light-induced spin crossover.

New field-induced single ion magnets based on prolate Er(iii) and Yb(iii) ions: tuning the energy barrierUeffby the choice of counterions within an N3-tridentate Schiff-base scaffold

Counterions modulate the structure and magnetic properties of rarely observed high-coordinate SIM species.

CERES: An ab initio code dedicated to the calculation of the electronic structure and magnetic properties of lanthanide complexes

We have developed and implemented a new ab initio code, Ceres (Computational Emulator of Rare Earth Systems), completely written in C++11, which is dedicated to the efficient calculation of the electronic structure and magnetic properties of the crystal field states arising from the splitting of the ground state spin-orbit multiplet in lanthanide complexes. The new code gains efficiency via an optimized implementation of a direct configurational averaged Hartree-Fock (CAHF) algorithm for the determination of 4f quasi-atomic active orbitals common to all multi-electron spin manifolds contributing to the ground spin-orbit multiplet of the lanthanide ion. The new CAHF implementation is based on quasi-Newton convergence acceleration techniques coupled to an efficient library for the direct evaluation of molecular integrals, and problem-specific density matrix guess strategies. After describing the main features of the new code, we compare its efficiency with the current state-of-the-art ab initio strategy to determine crystal field levels and properties, and show that our methodology, as implemented in Ceres, represents a more time-efficient computational strategy for the evaluation of the magnetic properties of lanthanide complexes, also allowing a full representation of non-perturbative spin-orbit coupling effects. © 2017 Wiley Periodicals, Inc.

Single-Molecule Magnet Behavior Enhanced by Synergic Effect of Single-Ion Anisotropy and Magnetic Interactions

As the simplest entity carrying intramolecular magnetic interactions, a dinuclear lanthanide complex serves as a model to investigate the effects of magnetic interactions on relaxation of magnetization, and importantly, it proves to be an efficient method to obtain robust single-molecule magnets via improving the communication between lanthanide centers. Here, three Dy₂ complexes (1, 2, 3) with a similar structural motif, namely, [Dy₂(HL)₂(NO₃)₂(CH₃CN)₂]·2CH₃CN (1), [Dy₂(HL)₂(NO₃)₂(DMF)₂]·2H₂O (2), and Dy₂(HL)₂(NO₃)₂(DMF)₄ (3), were successfully assembled. One critical difference found in this series of complexes is that the Dy center in complex 3 is coordinated by one more solvent molecule. Surprisingly, complex 3 exhibits the best magnet-like behavior, as evidenced by the high effective barrier and butterfly-type hysteresis, although the crystal field effect around Dy ions is weakened heavily. Ab initio calculations revealed the crucial reason is the significant synergic effect between single-ion anisotropy and magnetic interactions, i.e., not only the axiality of the Dy ion is improved efficiently but also the exchange magnetic interactions increased to the same order of magnitude to the dipolar interaction in 3. This effect mainly benefits from the elaborate modification of the local coordinate environment around the Dy ion, which results in a special arrangement of anisotropy axes different from the other two complexes. It demonstrates that the magnetic interactions could be effectively enhanced by means of deliberate local structural modulation.

Puzzling Lack of Temperature Dependence of the PuO2 Magnetic Susceptibility Explained According to Ab Initio Wave Function Calculations

The electronic structure and the magnetic properties of solid PuO₂ are investigated by wave function theory calculations, using a relativistic complete active space (CAS) approach including spin-orbit coupling. The experimental magnetic susceptibility is well reproduced by calculations for an embedded PuO₈^12- cluster model. The calculations indicate that the surprising lack of temperature dependence of the magnetic susceptibility χ of solid PuO₂ can be rationalized based on the properties of a single Pu⁴⁺ ion in the cubic ligand field of the surrounding oxygen ions. Below ∼300 K, the only populated state is the nonmagnetic ground state, leading to standard temperature-independent paramagnetism (TIP). Above 300 K, there is an almost perfect cancellation of temperature-dependent contributions to χ that depends delicately on the mixing of ion levels in the electronic states, their relative energies, and the magnetic coupling between them.

Key role of higher order symmetry and electrostatic ligand field design in the magnetic relaxation of low-coordinate Er(iii) complexes

Our theoretical analysis highlights that both symmetry and a suitable ligand field is required to obtain large barrier heights in SIMs. Key role of Lanthanide–halogen covalency in enhancing U_eff is discussed.

Strong direct exchange coupling and single-molecule magnetism in indigo-bridged lanthanide dimers

The first lanthanide–indigo complexes are described, including a dysprosium single-molecule magnet and one of the strongest exchange coupling constants measured in a gadolinium compound.

Configuration-averaged 4f orbitals in ab initio calculations of low-lying crystal field levels in lanthanide(iii) complexes

We propose an ab initio method that simplifies the CASSCF/RASSI–SO approach for crystal field levels and magnetic properties of lanthanide complexes.