Solid state structures and solution behaviour of tetranuclear lanthanide(III) carbonate-bridged coordination compounds of chiral 3 + 3 amine macrocycle

The linking of two dinuclear macrocyclic units of large triphenolic hexaazamine by two carbonate anions results in the formation of dimeric tetranuclear Sm(III), Eu(III) and Gd(III) complexes. These complexes were initially obtained serendipitously by fixation of atmospheric carbon dioxide and subsequently obtained in a rational way by the application of carbonate salts. The X-ray crystal structures of these isomorphic complexes show highly folded conformation of the macrocycle. This type of conformation is also confirmed by 2D NMR spectra of the Sm(III) complex. The ESI-MS and NMR spectra reveal also that these carbonate complexes exist in solution in two different forms that are in a concentration-dependent dynamic equilibrium.

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.

Mononuclear Dysprosium Alkoxide and Aryloxide Single-Molecule Magnets

Recent studies have shown that 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, which have provided the necessary geometrical control to improve SMM properties and to allow the intricate relaxation dynamics of Ln SMMs to be studied in detail. Here non‐aqueous Ln alkoxide and aryloxide chemistry applied to the synthesis of low‐coordinate mononuclear Ln SMMs are reviewed. The focus is on mononuclear Dy^III alkoxide and aryloxide SMMs with coordination numbers up to eight, covering synthesis, solid‐state structures and magnetic attributes. Brief overviews are also provided of mononuclear Tb^III, Ho^III, Er^III and Yb^III alkoxide and aryloxide SMMs.

Tuning the ligand field in seven-coordinate Dy(iii) complexes to perturb single-ion magnet behavior

Two mononuclear seven-coordinate Dy(iii) complexes with different strengths of ligand fields exhibit different slow magnetic relaxations.

A seven-coordinated DyIII single-ion magnet with C2v symmetry constructed by a multidentate Schiff-base ligand

Utilizing a flexible Schiff-base ligand with large steric hindrance helps to stabilize the seven-coordinated Ln^III complexes; Dy^III complex with C_2v low symmetry still displays the SIM behavior.

Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

A whole series of [Ln(H2O)4(Ala)2]26+ dimeric cationic lanthanide complexes with both L- and D-alanine enantiomers was synthesized. The single-crystal X-ray diffraction at 100 and 292 K shows the formation of two types of dimers (I and II) in crystals. Between the dimer centers, the alanine molecules behave as bridging (μ2-O,O'-) and chelating bridging (μ2-O,O,O'-) ligands. The first type of bridge is present in dimers I, while both bridge forms can be observed in dimers II. The IR and vibrational circular dichroism (VCD) spectra of all L- and D-alanine complexes were registered in the 1750-1250 cm-1 range as KBr pellets. Despite all the studied complexes are exhibiting similar crystal structures, the spectra reveal correlations or trends with the Ln-O1 distances which exemplify the lanthanide contraction effect in the IR spectra. This is especially true for the positions and intensities of some IR bands. Unexpectedly, the ν(C=O) VCD bands are quite intense and their composed shapes reveal the inequivalence of the C=O vibrators in the unit cell which vary with the lanthanide. Unlike in the IR spectra, the ν(C=O) VCD band positions are only weakly correlated with the change of Ln and the VCD intensities at most show some trends. Nevertheless, this is the first observation of the lanthanide contraction effect in the VCD spectra. Generally, for the heavier lanthanides (Ln: Dy-Lu), the VCD band maxima are very close to each other and the mirror reflection of the band of two enantiomers is usually better than that of the lighter Lns. DFT calculations show that the higher the multiplicity the higher the stability of the system. Actually, the molecular geometry in crystals (at 100 K) is well predicted based on the highest-spin structures. Also, the simulated IR and VCD spectra strongly depend on the Ln electron configuration but the best overall agreement was reached for the Lu complex, which is the only system with a fully filled f-shell.

Towards comparative investigation of Er- and Yb-based SMMs: the effect of the coordination environment configuration on the magnetic relaxation in the series of heteroleptic thiocyanate complexes

We prepared and studied two similar series of Er and Yb thiocyanates, involving [Ln(H₂O)₅(NCS)₃]·H₂O (1Er, 1Yb) as well as the molecular and ionic complexes with 2,2'-bipyridine (bpy) and 1,10-phenantroline (phen), [Ln(H₂O)(bpy)₂(NCS)₃]·0.5(bpy)·H₂O (2Er, 2Yb), [Ln(H₂O)(phen)₂(NCS)₃]·phen·0.5H₂O (3Er, 3Yb), [Hbpy][Ln(bpy)₂(NCS)₄]·H₂O (4Er, 4Yb) and [Hphen][Ln(phen)₂(NCS)₄] (5Er, 5Yb). All the complexes were found to exhibit the properties of field-induced single-molecule magnets. For 1Yb, the effective value of the energy barrier for magnetization reversal, Δ_eff/k_B, equals to 50 K, which is among the highest ones currently known for molecular SMMs based on Yb³⁺. The obtained data are discussed involving essential structural features of the complexes, namely the configuration of the Ln environment, i.e. its composition and geometry as well as mutual distribution of different donating centers. To the best of our knowledge, this work also involves experimental investigation of the largest and thus sufficiently representative series of similar mononuclear SMMs based on Er and Yb within one study.

Syntheses, crystal structures and magnetic properties of a series of luminescent lanthanide complexes containing neutral tetradentate phenanthroline-amide ligands

Six lanthanide compounds have been prepared from a neutral tetra-dentate ligand. Their luminescent and magnetic properties were investigated in detail.

A series of dysprosium-based hydrogen-bonded organic frameworks (Dy–HOFs): thermally triggered off → on conversion of a single-ion magnet

A series of dysprosium-based HOFs (Dy–HOFs) were designed and synthesized for the first time under solvothermal conditions. Herein, we achieved the magnetic off → on SIM switching of Dy–HOFs under thermal driving conditions.

Two mononuclear dysprosium(iii) complexes with their slow magnetic relaxation behaviors tuned by coordination geometry

We report here two field-induced single-ion magnets of Dy(iii), which present octahedral and pentagonal–bipyramidal coordination geometries, respectively, with their magnetic performances tuned by the coordination geometries of Dy(iii).

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.

A pair of mononuclear Dy(iii) enantiomers showing single-ion magnetic and ferroelectric properties

A new pair of Dy(iii)-β-diketonate enantiomers with chiral N,N′-donor ligands display chiroptical activities and ferroelectric and single-ion magnetic properties, and act as potential multifunctional molecule-based materials.

An intense luminescent Dy(iii) single-ion magnet with the acylpyrazolonate ligand showing two slow magnetic relaxation processes

A new Dy(iii)-acylpyrazolonate complex displays both intense yellow-light emission and single-ion magnet behavior with two slow magnetic relaxation processes, acting as a potential bifunctional material.

Investigation of magneto-structural correlation based on a series of seven-coordinated β-diketone Dy(iii) single-ion magnets with C2v and C3v local symmetry

Four field-induced single-ion magnets based on seven-coordinated Dy(iii) complexes have been prepared to explore the magnetism–structure relationship.

Chiral and kryptoracemic Dy(iii) complexes with field-induced single molecule magnet behavior

Crystalline mode modulation and magnetic relaxation manipulation can be realized by the introduction of different anions into mononuclear Dy(iii) single molecule magnets (SMMs).

Slow magnetic relaxation in mononuclear complexes of Tb, Dy, Ho and Er with the pentadentate (N3O2) Schiff-base dapsc ligand

AC measurements revealed field-induced single-ion magnet behavior of Dy and Er Kramers ion complexes. The properties of complexes were rationalized by superposition CF model.

Chiral six-coordinate Dy(iii) and Tb(iii) complexes of an achiral ligand: structure, fluorescence, and magnetism

Two new chiral six-coordinate lanthanide complexes are obtained using an achiral ligand. Complex [Zn₃Dy] displays field-induced slow magnetization relaxation, while complex [Zn₃Tb] exhibits intense green photofluorescence and triboluminescence.

Muffin-like lanthanide complexes with an N5O2-donor macrocyclic ligand showing field-induced single-molecule magnet behaviour

Three mononuclear lanthanide complexes of a 2-pyridylmethyl pendant-armed 15-membered ligand {L} with general formula [Ln(L)(H₂O)(NO₃)](NO₃)₂ (Ln = Tb (1), Dy (2), and Er (3)) are reported.

Dysprosium(iii) complexes with a square-antiprism configuration featuring mononuclear single-molecule magnetic behaviours based on different β-diketonate ligands and auxiliary ligands

Three mononuclear SMMs derived from three β-diketonate ligands and auxiliary ligands have been synthesized.

A nine-coordinated dysprosium(iii) compound with an oxalate-bridged dysprosium(iii) layer exhibiting two slow magnetic relaxation processes

A 2D oxalate-bridged dysprosium(iii) compound, formulated as [Dy(C₂O₄)_1.5(H₂O)₃]_n·2nH₂O (1), has been hydrothermally isolated.

Magnetic and photo-physical investigations into DyIII and YbIII complexes involving tetrathiafulvalene ligand

Three TTF-based complexes have been elaborated using β-diketonate Dy^III and Yb^III precursors. [Yb(tta)₃(L)]·2CH₂Cl₂ enlarges the scarce series of redox-active luminescent single-molecule magnets with correlation between emissive and magnetic properties.