Size-Controlled Hapticity Switching in [Ln(C9H9)(C8H8)][Ln(C_{9}H_{9})(C_{8}H_{8})] Sandwiches

Sandwich complexes of lanthanides have recently attracted a considerable amount of interest due to their applications as Single Molecule Magnet (SMM). Herein, a comprehensive series of heteroleptic lanthanide sandwich complexes ligated by the cyclononatetraenyl (Cnt) and the cyclooctatetraenyl (Cot) ligand [Ln(Cot)(Cnt)] (Ln=Tb, Dy, Er, Ho, Yb, and Lu) is reported. The coordination behavior of the Cnt ligand has been investigated along the series and shows different coordination patterns in the solid-state depending on the size of the corresponding lanthanide ion without altering its overall anisotropy. Besides the characterization in the solid state by single-crystal X-ray diffraction and in solution by $^{1}H$NMR, static magnetic studies and ab initio computational studies were performed

Magnetic hysteresis and large coercivity in bisbenzimidazole radical-bridged dilanthanide complexes

International audienceA judicious combination of radical ligands innate to diffuse spin orbitals with paramagnetic metal ions elicits strong magnetic exchange coupling which leads to properties important for future technologies. This metal-radical approach aids in effective magnetic communication of especially lanthanide ions as their 4f orbitals are contracted and not readily accessible. Notably, a high spin density on the donor atoms of the radical is required for strong coupling. Such molecules are extremely rare owing to high reactivity rendering their isolation challenging. Herein, we present two unprecedented series of bisbenzimidazolebased dilanthanide complexes [(Cp*(2)Ln)(2)(mu-Bbim)] (1-Ln = Gd, Tb, Dy, Bbim = 2,2'-bisbenzimidazole) and [K(crypt-222)][(Cp*(2)Ln)(2)(mu-Bbimc)] -(2-Ln = Gd, Tb, Dy), where the latter contains the first Bbim(3)- c radical matched with any paramagnetic metal ion. The magnetic exchange constant for 2-Gd of J = -1.96(2) cm(-1) suggests strong antiferromagnetic Gd-radical coupling, whereas the lanthanides in 1-Gd are essentially uncoupled. Ab initio calculations on 2-Tb and 2-Dy uncovered coupling strengths of -4.8 and -1.8 cm(-1). 1-Dy features open hysteresis loops with a coercive field of Hc of 0.11 T where the single-molecule magnetism can be attributed to the single-ion effect due to lack of coupling. Excitingly, pairing the effective magnetic coupling with the strong magnetic anisotropy of Dy results in magnetic hysteresis with a blocking temperature TB of 5.5 K and coercive field H-C of 0.54 T, ranking 2-Dy as the second best dinuclear single-molecule magnet containing an organic radical bridge. A Bbim(4)- species is formed electrochemically hinting at the accessibility of Bbim-based redox-active materials

Synthesis and Structures of Tris(cyclononatetraenyl) Rare-Earth Complexes [Ln(C9H9)(3)] (Ln = Y, Gd, Tb, Dy, Ho, Er, Tm)

International audienceThe article reports the synthesis and structural characterization of a series of Ln(C9H9)(3) complexes with the cyclononatetraenyl (Cnt, C9H9) ligand (Ln = Y, Gd, Tb, Dy, Ho, Er, Tm). The Yb and Sm complexes were not obtained, and the reaction of the potassium salt of the Cnt ligand with trivalent halide salts of the corresponding metals led to the known bis-Cnt sandwich compounds Ln(C9H9)(2). The X-ray diffraction studies on the trivalent complexes show that the Cnt ligand is significantly bent in order to accommodate the large size of the ligand while it maintains its aromaticity. When the size of the lanthanide ion decreases, the ligand does not switch away but swings over the metal ion in order to maximize the electrostatic interactions. H-1 NMR and UV-visible spectra, as well as the solid-state magnetism, were recorded. UV-visible spectroscopy highlights a remarkable charge-transfer band in the Tm complex, while ligand-based transitions are principally observed with all other metal ions. The magnetic behavior of the series agrees with trivalent lanthanide ions, and the computations at the CASSCF level confirm the trivalent electronic structure

Coordination anion effects on the geometry and magnetic interaction of binuclear Dy-2 single-molecule magnets

International audienceTwo new dimeric dysprosium(III) complexes, [Dy(HL)(SCN)]·2CHCN (1) and [Dy(HL)(NO)]·2CHCN·2HO (2), have been assembled using the HL multidentate ligand (HL = 2,2'-((((2-hydroxy-5-methyl-1,3-phenylene)bis(methylene))bis((pyridin-2-ylmethyl)azanediyl))bis(methylene))diphenol). The use of different coordination anions for the two complexes results in distinct coordination geometries of the metal sites. The Dy centers in complexes 1 and 2 display capped octahedron and triangular dodecahedron coordination geometries, respectively. Consequently, the two compounds exhibit distinct dc and ac magnetic properties. Complex 1 behaves as a single molecule magnet (SMM) while no SMM behavior is observed for complex 2. Although complexes 1 and 2 possess a similar core of DyO, their different coordination anions lead to two distinct magnetic interactions, namely ferromagnetic and antiferromagnetic, respectively. calculations reveal that these interactions may result from strong intramolecular dipolar couplings that are ferromagnetic for 1 but antiferromagnetic for 2, while exchange couplings are antiferromagnetic in both cases

Toroidal moment and dynamical control in luminescent 1D and 3D terbium calixarene compounds

International audienceA toroidal moment can be generated spontaneously in inorganic (atom-based) ferrotoroidic materials that breaks both time-reversal and space-inversion symmetries, attracting great attention in solid-state chemistry and physics. In the field of molecular magnetism, it can also be achieved in lanthanide (Ln) involved metal-organic complexes usually with a wheel-shaped topological structure. Such complexes are called single-molecule toroics (SMTs), presenting unique advantages in spin chirality qubits and magnetoelectric coupling. However, to date, the synthetic strategies of SMTs have remained elusive, and the covalently bonded three-dimensional (3D) extended SMT has not hitherto been synthesized. Here, two luminescent Tb(iii)-calixarene aggregates with architectures of 1D chain (1) and 3D network (2) both containing the square Tb-4 unit have been prepared. Their SMT characteristics deriving from the toroidal arrangement of the local magnetic anisotropy axes of Tb(iii) ions in the Tb-4 unit have been investigated experimentally with the support of ab initio calculations. To the best of our knowledge, 2 is the first covalently bonded 3D SMT polymer. Remarkably, solvato-switching of SMT behavior has also been achieved for the first time by desolvation and solvation processes of 1

Edaravone-Based Mononuclear Dysprosium(III) Single-Molecule Magnets

International audienceUsing an edaravone-based aryloxide ligand, we assemble four new mononuclear Dy(III) compounds, [Dy(L1)(2)(CH3OH)(2)]middotBr (1); [Dy(L1)(2)(CH3OH)(2)]middotCl (2); [Dy(L1)(2)(CH3OH)(NO3)] (3); and [Dy(L2)(3)]middot2CH(3)OHmiddotH(2)O (4) (where L1 = methyl-substituted and L2 = p-tolyl-substituted ligands with NNO-tridentate coordination environments). As revealed by the magneto-structural and ab initio calculations, the complexes exhibited a slow relaxation of the magnetization at zero applied magnetic field where their magnetic properties were subtly tuned via chemical modifications on the dominant crystal field interaction. For the complexes with L1 analogue under eight-coordination, complexes 1 and 2 (D-4d symmetry) with noncoordinated halides showed better magnetic properties as compared to complex 3 (C-2v symmetry) due to the presence of a strongly coordinated nitrate anion that leads to a change in the structural arrangement. However, complex 4 (C-4v symmetry) with nine-coordination was found structurally unfavorable comparatively due to the coordination of an additional third ligand (L2) that leads to a higher coordination number as a result of the substituent change. Therefore, the presented compounds exhibit ligand substituent- as well as counterion-dependent magnetic property variations. A relatively higher effective energy barrier (U-eff) was obtained for the compounds having halide counter anions as compared with the neutral complexes. Moreover, the ab initio calculations revealed that the transition magnetic moment probabilities for these compounds present very small or even vanishing quantum tunneling of magnetization between the ground-state Kramers doublets and indicate that the slow relaxation might proceed through higher excited states. Finally, the described new compounds are expected to advance the aryloxide single-molecule magnets

Size‐Controlled Hapticity Switching in [Ln(C9H9)(C8H8)] Sandwiches

International audienceSandwich complexes of lanthanides have recently attracted a considerable amount of interest due to their applications as Single Molecule Magnet (SMM). Herein, a comprehensive series of heteroleptic lanthanide sandwich complexes ligated by the cyclononatetraenyl (Cnt) and the cyclooctatetraenyl (Cot) ligand [Ln(Cot)(Cnt)] (Ln=Tb, Dy, Er, Ho, Yb, and Lu) is reported. The coordination behavior of the Cnt ligand has been investigated along the series and shows different coordination patterns in the solid-state depending on the size of the corresponding lanthanide ion without altering its overall anisotropy. Besides the characterization in the solid state by single-crystal X-ray diffraction and in solution by 1 H NMR, static magnetic studies and ab initio computational studies were performed

Molecular Lanthanide Switches for Magnetism and Photoluminescence

International audienceSolvation of [(η9-CNT)Ln(η8-COT)] (Ln = La, Ce, Nd, Tb, Er; CNT = cyclononatetraenyl, i.e., C9H9-; COT = cyclooctatetraendiid, i.e., C8H82-) complexes with tetrahydrofuran (THF) gives rise to neutral [(η4-CNT)Ln(thf)2(η8-COT)] (Ln = La, Ce) and ionic [Ln(thf)x(η8-COT)][CNT] (x = 4 (Ce, Nd, Tb), 3 (Er)) species in a solid-to-solid transformation. Due to the severe distortion of the ligand sphere upon solvation, these species act as switchable luminophores and single-molecule magnets. The desolvation of the coordinated solvents can be triggered by applying a dynamic vacuum, as well as a temperature gradient stimulus. Raman spectroscopic investigations revealed fast and fully reversible solvation and desolvation processes. Moreover, we also show that a Nd:YAG laser can induce the necessary temperature gradient for a self-sufficient switching process of the Ce analogue in a spatially resolved manner