The effect of magnetic coupling along the magnetic axis on slow magnetic relaxation in DyIII complexes with D5h configuration based on an aggregation-induced-emission-active ligand

The adjustment of crystal symmetry and intramolecular magnetic coupling is of great importance for the construction of high-performance single-molecule magnets. By using an aggregation-induced-emission-active pyridine-carbohydrazone-based Schiff base ligand and phosphine oxides, four dinuclear and one one-dimensional DyIII-based complexes, [Dy2(TPE-pc)2(Bu3PO)2Cl2]·2CH3CN·2H2O (1), [Dy2(TPE-pc)2(Cy3PO)2Cl2] (2), [Dy2(TPE-pc)2(MePA)2Cl2]·2CH3OH (3), [Dy2(TPE-pc)2(Ph3PO)2Cl2]2 (4) and [Dy2(TPE-pc)2(DPPO)Cl2]n (5) (H2TPE-pc = (E)-N'-(2-hydroxy-5-(1,2,2-triphenylvinyl)benzylidene)picolinohydrazide, MePA = N-phenyl-N',N''-bis(morpholinyl) phosphoric triamide, DPPO = piperazine-1,4-diylbis(diphenyl phosphine oxide)), were isolated. All complexes are made up of an enol oxygen-bridged Dy2 unit, where DyIII ions possess a pentagonal bipyramidal geometry with pseudo D5h symmetry. Magnetic measurements reveal that intramolecular DyIII-DyIII couplings are ferromagnetic and all complexes display a significant slow magnetic relaxation phenomenon below 30 K under a zero dc field. Ab initio calculations indicate that the anisotropic magnetic axes of all DyIII ions are approximately perpendicular to the higher-order symmetric axes in all complexes, and that DyIII-DyIII magnetic couplings along the magnetic axes effectively suppress the ground state quantum tunneling effect of magnetization and promote the occurrence of slow magnetic relaxation. Raman relaxation prevails in all complexes. In addition, the H2TPE-pc ligand shows an aggregation-induced emission (AIE) effect; however, all complexes exhibit an aggregation-caused quenching (ACQ) phenomenon.

Dinuclear Fluoride Single-Bridged Lanthanoid Complexes as Molecule Magnets: Unprecedented Coupling Constant in a Fluoride-Bridged Gadolinium Compound

A new synthetic method allows isolating fluoride-bridged complexes Bu₄N{[M(3NO₂,5Br-H₃L^1,1,4)]₂(μ-F)} (M = Dy, 1; M = Ho, 2; M = Gd, 3) and Bu₄N{[Dy(3Br,5Cl-H₃L^1,2,4)]₂(μ-F)}·2H₂O, 4·2H₂O. The crystal structures of 1·5CH₃C₆H₅,·2·2H₂O·0.75THF, 3, and 4·2H₂O·2THF show that all of them are dinuclear compounds with linear single fluoride bridges and octacoordinated metal centers. Magnetic susceptibility measurements in the temperature range of 2–300 K reveal that the Gd^III ions in 3 are weakly antiferromagnetically coupled, and this constitutes the first crystallographically and magnetically analyzed gadolinium complex with a fluoride bridge. Variable-temperature magnetization demonstrates a poor magnetocaloric effect for 3. Alternating current magnetic measurements for 1, 2, and 4·2H₂O bring to light that 4·2H₂O is an SMM, 1 shows an SMM-like behavior under a magnetic field of 600 Oe, while 2 does not show relaxation of the magnetization even under an applied magnetic field. In spite of this, 2 is the first fluoride-bridged holmium complex magnetically analyzed. DFT and ab initio calculations support the experimental magnetic results and show that apparently small structural differences between 1 and 4·2H₂O introduce important changes in the dipolar interactions, from antiferromagnetic in 1 to ferromagnetic in 4·2H₂O.

Dinuclear linear fluoride single-bridged Dy^III, Ho^III, and Gd^III complexes are systematically obtained from mononuclear aquo-complexes, with the Dy^III ones showing slow relaxation of the magnetization and the Gd^III one revealing a weak AF coupling through the Gd−F−Gd bridge.

Lanthanoid-Anilato Complexes and Lattices

In this review, we describe all the structurally characterized complexes containing lanthanoids (Ln, including La and group 3 metals: Y and Lu) and any anilato-type ligand (3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone dianion = C6O4X22−). We present all the anilato-Ln compounds including those where, besides the anilato-type ligand, there is one or more coligands or solvent molecules coordinated to the lanthanoid ions. We show the different structural types observed in these compounds: from discrete monomers, dimers and tetramers to extended 1D, 2D and 3D lattices with different topologies. We also revise the magnetic properties of these Ln-anilato compounds, including single-molecule magnet (SMM) and single-ion magnet (SIM) behaviours. Finally, we show the luminescent and electrochemical properties of some of them, their gas/solvent adsorption/absorption and exchange capacity and the attempts to prepare them as thin films.

Cerium-quinone redox couples put under scrutiny

Homoleptic cerous complexes Ce[N(SiMe₃)₂]₃, [Ce{OSi(OtBu)₃}₃]₂ and [Ce{OSiⁱPr₃}₃]₂ were employed as thermally robust, weakly nucleophilic precursors to assess their reactivity towards 1,4-quinones in non-aqueous solution. The strongly oxidizing quinones 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or tetrachloro-1,4-benzoquinone (Cl₄BQ) readily form hydroquinolato-bridged ceric complexes of the composition [(Ce^IVL₃)₂(μ₂-O₂C₆R₄)]. Less oxidising quinones like 2,5-di-tert-butyl-1,4-benzoquinone (tBu₂BQ) tend to engage in redox equilibria with the ceric hydroquinolato-bridged form being stable only in the solid state. Even less oxidising quinones such as tetramethyl-1,4-benzoquinone (Me₄BQ) afford cerous semiquinolates of the type [(Ce^IIIL₂(thf)₂)(μ₂-O₂C₆Me₄)]₂. All complexes were characterised by X-ray diffraction, ¹H, ¹³C{¹H} and ²⁹Si NMR spectroscopy, DRIFT spectroscopy, UV-Vis spectroscopy and CV measurements. The species putatively formed during the electrochemical reduction of [Ce^IV{N(SiMe₃)₂}₃]₂(μ₂-O₂C₆H₄) could be mimicked by chemical reduction with Co^IICp₂ yielding [(Ce^III{N(SiMe₃)₂}₃)₂(μ₂-O₂C₆H₄)][Co^IIICp₂]₂.

Manipulating On/Off Single-Molecule Magnet Behavior in a Dy(III)-Based Photochromic Complex

Exploitation of room temperature (RT) photochromism and photomagnetism to induce single-molecule magnet (SMM) behavior has potential applications toward optical switches and magnetic memories, and remains a tremendous challenge in the development of new bulk magnets. Herein, a series of chain complexes [Ln₃(H-HEDP)₃(H₂-HEDP)₃]·2H₃-TPT·H₄-HEDP·10H₂O (QDU-1; Ln = Dy (QDU-1(Dy)), Gd (QDU-1(Gd)), and Y (QDU-1(Y)); HEDP = hydroxyethylidene diphosphonate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine) were synthesized by solvothermal reactions. All the compounds exhibited reversible photochromic and photomagnetic behaviors via UV light irradiation at RT, induced by the photogenerated radicals via a photoinduced electron transfer (PET) mechanism. More importantly, the PET process induced significant variations in magnetic interactions for the Dy(III) congener. Strong ferromagnetic coupling with remarkably slow magnetic relaxation without applied dc fields was observed between Dy^III ions and photogenerated O^• radicals, showing SMM behavior after RT illumination. For the first time, we observed the reversible RT photochromism and photomagnetism in the lanthanide-based materials. This work realized the radicals-actuated on/off SMM behavior via RT light irradiation, providing a new strategy for constructing the light-induced SMMs.

Water-stable LnIII-based coordination polymers displaying slow magnetic relaxation and luminescence sensing properties

Six Ln-CPs were synthesized: Dy-CP shows slow magnetic relaxation, and Eu-CP and Tb-CP exhibit recyclable and multi-responsive sensing for Fe³⁺, MnO₄⁻, Cr^VI-anions (CrO₄²⁻, Cr₂O₇²⁻) and TNP in an aqueous system.

Unprecedented intramolecular pancake bonding in a {Dy2} single-molecule magnet

The first example of unique coordination induced intramolecular pancake bonding was achieved through the reduction of two bis(pyrazolyl)-tetrazine ligands.

Three 3D LnIII-MOFs based on a nitro-functionalized biphenyltricarboxylate ligand: syntheses, structures, and magnetic properties

Cluster, chain or layer-based 3D Ln-MOFs have been synthesized and they exhibit ferromagnetic or antiferromagnetic interactions. Furthermore, the Dy-MOF shows slow relaxation behavior.

Versatility of cyclooctatetraenyl ligands in rare earth metal complexes of the [M2(COT)3(THF)2] (M = Y and La) type

Two new organometallic cyclooctatetraenyl complexes of the type [M2(COT)3(THF)2] (M = Y and La) have been prepared, using optimized synthetic procedures, and fully characterized by X-ray diffraction analysis, IR and 1H NMR spectroscopies. The structures can be represented as formed by the double-decker [M(COT)2]- anion with an asymmetrically bound cationic [M(COT)(THF)2]+ unit. The COT rings in the anionic sandwich are not equidistant from the metal with the M-COTcentroid distances measuring at 1.991(5) Å and 2.074(5) Å for [Y(COT)2]-vs. 2.045(4) Å and 2.154(5) Å for [La(COT)2]-. The sandwich fragments are η2-coordinated to the second metal center with the average M-C distances of 2.837(4) Å and 2.879(5) Å for yttrium and lanthanum complexes, respectively. The M-COTcentroid distances in the cationic unit are 1.962(4) Å for the former and 2.009(2) Å for the latter.

Single-molecule magnet behaviour in a Dy(iii) pentagonal bipyramidal complex with a quasi-linear Cl–Dy–Cl sequence

Slow relaxation of magnetization in a chloride pentagonal bipyramidal complex.

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).

Electro-activity and magnetic switching in lanthanide-based single-molecule magnets

The present work reviews switching of single-molecule magnetic behaviour achieved through various stimuli such as temperature, light irradiation, redox processes, solvation/desolvation, and magnetic field.

Dinuclear Dy2 Single-Molecule Magnets: Functional Modulation on the Bridging Ligand and Different Relaxation Performances within the Single-Crystal to Single-Crystal System

Crystal structures, single-molecule magnetic behavior, and ab initio calculations of four new phenoxo-bridged dinuclear dysprosium complexes and their gadolinium(III) analogues are explored. Complexes [Dy₂ (DMOMP)₂ (DBM)₄ ]₂ ⋅CHCl₃ (1; DMOMP=1-methyl-3,5-dimethoxy-4-hydroxybenzene, DBM=1,3-diphenylpropane-1,3-dione); [Dy₂ (DMOAP)₂ (DBM)₄ ]₂ ⋅CHCl₃ (2; DMOAP=syringaldehyde); Dy₂ (DMOEP)₂ (DBM)₄ (3; DMOEP=methyl syringate); and solvent-free Dy₂ (DMOMP)₂ (DBM)₄ (4), which is obtained by the transformation of single crystal into single crystal from 1, have nearly identical core structures and only differ in the substituents at the para position of the phenol moieties of the bridging ligand. In this system, the electronic effects are efficiently implemented to significantly modify the ligand field strength and exchange coupling by modulating the substituents on the phenol backbone. The effective energy barrier (U_eff ) of magnetization reversal is improved significantly to fivefold magnitude, at most, and the hysteresis temperature up to 3.5 K by deliberately using the electron-withdrawing substituent to replace the electron-donating one. The origin of the two relaxation processes in 1 is mostly attributed to the existence of two molecules in one unit, which is illuminated by means of the transformation of single crystal into single crystal.

Exchange coupling and single molecule magnetism in redox-active tetraoxolene-bridged dilanthanide complexes

Tetraoxolene radical-bridged lanthanide SMM systems were prepared for the first time by reduction of the respective neutral compounds. Magnetic measurements reveal the profound influence of the radical center on magnetic behavior. Strong magnetic couplings are revealed in the radical species, which switch on SMM behavior under zero applied field for DyIII and TbIII compounds. HFEPR spectra unravel the contributions of the magnetic coupling and the magnetic anisotropy. For GdIII this results in much more accurate magnetic coupling parameters with respect to bulk magnetic measurements.

Eight homodinuclear lanthanide complexes prepared from a quinoline based ligand: structural diversity and single-molecule magnetism behaviour

Eight dinuclear complexes are prepared and characterized; complex 6 exhibits SMM behavior with a U_eff value of 14.83 K.