A Chiral and Polar Single-Molecule Magnet: Synthesis, Structure, and Tracking of Its Formation Using Mass Spectrometry

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Two Pairs of Homochiral Parallelogram-like Dy4 Cluster Complexes with Strong Magneto-Optical Properties

Two pairs of homochiral Dy(III) tetranuclear cluster complexes derived from (+)/(-)-3-trifluoroacetyl camphor (D-Htfc/L-Htfc), [Dy4(OH)2(L1)4(D-tfc)2(DMF)2]·4DMF (D-1) [H2L1 = (E)-2-(2-hydroxy-3-methoxybenzylideneamino)phenol)]/[Dy4(OH)2(L1)4(L-tfc)2(DMF)2]·4DMF (L-1) and [Dy4(OH)2(L2)4(D-tfc)2(DMF)2]·2H2O·3MeCN (D-2) [H2L2 = (E)-3-(2-hydroxy-3-methoxybenzylideneamino)naphthalen-2-ol]/[Dy4(OH)2(L2)4(L-tfc)2(DMF)2]·2H2O·3MeCN (L-2), were synthesized at room temperature, which have a Dy4 parallelogram-like core. The magnetic studies revealed that D-1 exhibits single-molecule magnet (SMM) behavior under zero dc magnetic field, and its magnetic relaxation has a distinct Raman process in addition to the Orbach process, with the Ueff/k value of 57.5 K and the C value of 28.27 s-1K-2.14; while D-2 displays dual magnetic relaxation behavior at 0 Oe field, with the Ueff/k value 114.8 K for the slow relaxation process (SR) and the C value of 10.656 s-1K-5.80 for the fast relaxation process (FR), respectively. Theoretical calculations indicated that the conjugated groups (phenyl vs naphthyl) of the Schiff base bridging ligands (H2L1 and H2L2) significantly affect the intramolecular magnetic interactions between the Dy3+ ions and ultimately lead to different relaxations. Furthermore, magnetic circular dichroism (MCD) measurements showed that these two pairs of Dy4 enantiomers exhibit strong room temperature magneto-optical Faraday effects; notably, increasing the conjugated group on the Schiff base bridging ligand is beneficial to enhancing the magneto-optical Faraday effects.

Asymmetric Assembly of Chiral Lanthanide(III) Tetranuclear Cluster Complexes Using Achiral Mixed Ligands: Single-molecule Magnet Behavior and Magnetic Entropy Change

It is challenging to use achiral ligands to spontaneously construct chiral molecular magnets. In this work, two new Ln₄ cluster complexes based on N,N'-(1,3-propanediyl)bis[N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]amine] (H₆L) have been assembled, which are crystallized in a chiral space group due to the asymmetric distribution of acetate (OAc^-) groups and hexafluoroacetylacetonate (F₆acac^-) groups on both sides of the parallelogram-like Ln₄ core. Complex 1, [Dy₄(H₃L)₂(OAc)₃(F₆acac)₃]·5MeOH·2H₂O, exhibits single-molecule magnet properties at the zero field with the U _eff/k value of 48.4 K; notably, besides the Orbach process, the Raman process is also prominent for the magnetic relaxation of 1. Complex 2, [Gd₄(H₃L)₂(OAc)₃(F₆acac)₃]·4MeOH·2.5H₂O, displays a large magnetocaloric effect, whose largest -ΔS _m value is 21.88 J kg^-1 K^-1 (when T = 2 K and ΔH = 5 T); it thus can be utilized as a good magnetic refrigeration molecular material.

Crystal structure of di-μ-chlorido-bis{chlorido[(−)-5,6-pinenebipyridine]cobalt(II)} aquadichlorido[(−)-5,6-pinenebipyridine]cobalt(II)

The crystal structure of [Co2Cl4(C17H18N2)2][CoCl2(C17H18N2)(H2O)] or [Co(L)Cl(μ-Cl)]2[Co(L)(Cl)2(OH2)], where L is the enantiopure bidentate ligand (−)-5,6-pinenebipyridine (C17H18N2), has been determined. Crystals suitable for X-ray structure analysis were obtained by slow evaporation of an ethanolic solution containing equimolar amounts of L and CoCl2·6H2O. The CoII cations all have a coordination number of five, and in each case the coordination polyhedron is a trigonal bipyramid. The Co—N bonds lengths range from 2.037 (7) to 2.195 (7) Å, and Co—Cl bonds lengths range from 2.284 (2) to 2.509 (2) Å. The asymmetric unit contains two discrete complexes, one dinuclear and the other mononuclear. Between the two molecules, two types of intermolecular interactions have been evidenced: π–π stackings involving the bipyridine units, and O—H...Cl hydrogen bonds between the hydrogen atoms of the aqua ligand coordinating to the mononuclear complex and the non-bridging chlorido ligand coordinating to the dinuclear molecule. These interactions lead to a two-dimensional supramolecular arrangement parallel to the ab plane.

Field-induced slow magnetic relaxation behaviours in binuclear cobalt(II) metallocycle and exchange-coupled cluster

Precise control of structures and magnetic properties of a molecular material constitutes an important challenge to realize the tailor-made magnetic function. Herein, we reported that the ligand-directed coordination self-assembly of...

Crystal structure, assembly process, and single-molecule magnet behavior of a triangular prismatic {Co9} cluster

The crystal structure, assembly process and magnetic properties of a triangular prismatic [Co9(btdpa)3(CH2OCH2OH)6]·3.5H2O were reported: the cluster exhibits slow magnetization relaxation of single molecule magnets at zero field.

Bottom-up synthesis strategy of a two-dimensional {Fe5} cluster-based coordination polymer: stepwise formation of a {Fe5} cluster and its dimension augmentation

A 2D cluster-based coordination polymer of {Fe5}-2D was developed by hierarchical dimension augmentation from its 1D coordination polymer of {Fe5}-1D and discrete 0D cluster of {Fe5}-0D. And a possible bottom-up synthesis mechanism was proposed.

The dominance of sulfate over two organic ligands in the solvothermal assembly of an undecanuclear cobaltous cluster: crystallography and mass spectrometry

An unexpected dominance of the coordination affinity of the sulfate anion over those of two organic chelating ligands, (1-methyl-1H-benzo[d]imidazol-2-yl)methanol (Hmbm) and pyridin-2-ylmethanamine (pma), was observed during the study of the solvothermal assembly of [Co11(mbm)6(pma)2(SO4)8(H2O)6(CH3OH)6]·5CH3OH (1), from CoSO4·7H2O at 100 °C in methanol. ESI-MS of solutions at different periods of the assembly reveal a hierarchical sequence, [Co1] → [Co2] → [Co3] → [Co4] → [Co5] → [Co9], where the lower nuclearity species are richer in Co2+ and SO42- before the inclusion of more mbm ligands at the last step. Its crystal structure consists of an almost symmetrical wheel of nine cobalt atoms, [Co9(mbm)6(SO4)8(H2O)6] in edge-sharing octahedral coordination arranged in triangles with two peripheral dangling [Co(pma)(CH3OH)3]. The sulfate ions exhibit three different coordination modes, two in μ6-, two in μ3- and four as μ2-bridging. Its thermal, optical and magnetic properties are also reported.