Single-molecule Magnet Properties Research Articles

Dynamic Magnetic Susceptibility Method in Studies of Coordination Compounds

The measurement of the dynamic magnetic susceptibility is a universal method, which is used for the evaluation of magnetic properties of single molecule magnets by scientists all over the world. An information in the Russian scientific literature that can be useful for practical mastering of this method is presently insufficient. To fill this gap, in this work we present a detailed procedure of a magnetochemical experiment for observing slow magnetic relaxation in coordination compounds of 3d- and 4f-element ions and the complete characterization of the dynamics of the magnetic behavior. Special attention is given to usually omitted but important details related to all stages of studying the magnetic relaxation dynamics. The main variants of sample preparation are described, the logics of the construction of a measuring sequence and the procedure of experimental data processing are discussed, and advantages and drawbacks of some programs of the calculation of magnetic relaxation dynamics data are considered. The main concepts and equations used in experimental data analysis are presented, and the primary conclusions that can be made from the obtained results are proposed.

Enhancement of Single-Molecule Magnet Properties by Manipulating Intramolecular Dipolar Interactions.

A new single-molecule magnet (SMM) complex [K(18-crown-6)][(COT)Er(µ-Cl)3Er(COT)] (Er2Cl3, COT=cyclooctatetraenide dianion) is obtained by the reaction of [(COT)Er(µ-Cl)(THF)]2 (Er2Cl2, THF=tetrahydrofuran) with an equivalent of KCl in the presence of 18-crown-6. The two COT-Er units in the newly formed complex are triply bridged by µ-Cl ligands, leading to the "head-to-tail" alignment of the magnetic easy axes distinctly different from the "staggered" arrangement in the precursor complex. This structural transformation has led to significantly enhanced intramolecular dipolar interactions and a reduced transverse component of the crystal fields, increasing the energy barrier from 150(8) K for Er2Cl2 to 264(4) K for Er2Cl3 and extending its magnetic relaxation time at 2 K by 2500 times with respect to Er2Cl2. More importantly, the blocking temperature increased from lower than 2 K for Er2Cl2 to 8 K for Er2Cl3, and the magnetic hysteresis loops at 2 K changed from butterfly-shaped for Er2Cl2 to open hysteresis loop with coercive force of 7 kOe for Er2Cl3. These results suggest that the properties of SMMs can be effectively tuned and improved by rationally arranging magnetic spins via molecular engineering.

Thermal Jahn-Teller Distortion Changes and Slow Relaxation of Magnetization in Mn(III) Schiff Base Complexes.

The impact that the anion and alkyl group has on the electronic structures and magnetic properties of four mononuclear Mn(III) complexes is explored in [Mn(salEen-Br)2]Y (salEen-Br = 2-{[2-(ethylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 1 and BF4-·1/3CH2Cl2 2) and [Mn(salBzen-Br)2]Y (salBzen-Br = 2-{[2-(benzylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 3 and BF4- 4). X-ray structures of [Mn(salEen-Br)2]ClO4·0.45C6H14 1-hexane, [Mn(salEen-Br)2]BF4·0.33CH2Cl2·0.15C6H14 2-dcm-hexane, and 3-4 reveal that they crystallize in ambient conditions in the monoclinic P21/c space group. Lowering the temperature, 2-dcm-hexane uniquely exhibits a structural phase transition toward a monoclinic P21/n crystal structure determined at 100 K with the unit cell trebling in size. Remarkably, at room temperature, the axially elongated Jahn-Teller axis in 2-dcm-hexane is poorly defined but becomes clearer at low temperature after the phase transition. Magnetic susceptibility measurements of 1-4 reveal that only 3 and 4 show slow relaxation of magnetization with Δeff/kB = 27.9 and 20.7 K, implying that the benzyl group is important for observing single-molecule magnet (SMM) properties. Theoretical calculations demonstrate that the alkyl group subtly influences the orbital levels and therefore very likely the observed SMM properties.

Dynamic Magnetic Susceptibility Method in Studies of Coordination Compounds

The measurement of the dynamic magnetic susceptibility is a universal method, which is used for the evaluation of magnetic properties of single molecule magnets by scientists all over the world. An information in the Russian scientific literature that can be useful for practical mastering of this method is presently insufficient. To fill this gap, in this work we present a detailed procedure of a magnetochemical experiment for observing slow magnetic relaxation in coordination compounds of 3d- and 4f-element ions and the complete characterization of the dynamics of the magnetic behavior. Special attention is given to usually omitted but important details related to all stages of studying the magnetic relaxation dynamics. The main variants of sample preparation are described, the logics of the construction of a measuring sequence and the procedure of experimental data processing are discussed, and advantages and drawbacks of some programs of the calculation of magnetic relaxation dynamics data are considered. The main concepts and equations used in experimental data analysis are presented, and the primary conclusions that can be made from the obtained results are proposed.

Challenges for exploiting nanomagnet properties on surfaces.

Molecular complexes with single-molecule magnet (SMM) or qubit properties, commonly called molecular nanomagnets, are great candidates for information storage or quantum information processing technologies. However, the implementation of molecular nanomagnets in devices for the above-mentioned applications requires controlled surface deposition and addressing the nanomagnets' properties on the surface. This Perspectives paper gives a brief overview of molecular properties on a surface relevant for magnetic molecules and how they are affected when the molecules interact with a surface; then, we focus on systems of increasing complexity, where the relevant SMMs and qubit properties have been observed for the molecules deposited on surfaces; finally, future perspectives, including possible ways of overcoming the problems encountered so far are discussed.

A Family of Lanthanoid‐Sodium Multifunctional Coordination Polymers: Single‐Molecule Magnet, Luminescent and Magnetocaloric Properties

AbstractIn this paper we report the microwave assisted synthesis and characterization of a family of Na−Ln coordination polymers (CPs) of formula [NaDy2(MeCOO)2(SALOH)5(chpH)2] (1Ln, Ln=Eu, Gd, Tb, Dy, Ho, Y). The Na+ cations isolate Ln2 units in a one‐dimensional polymer. By changing the lanthanoid ions, we attain Single Molecule Magnet properties (1Dy), luminescent properties (1Eu, 1Tb, 1Ho), a diamagnetic material (1Y) and a material that presents magnetocaloric effect (1Gd).

Slow magnetic relaxation in a europium(II) complex.

Single-ion anisotropy is vital for the observation of Single-Molecule Magnet (SMM) properties (i.e., a slow dynamics of the magnetization) in lanthanide-based systems. In the case of europium, the occurrence of this phenomenon has been inhibited by the spin and orbital quantum numbers that give way to J = 0 in the trivalent state and the half-filled population of the 4f orbitals in the divalent state. Herein, by optimizing the local crystal field of a quasi-linear bis(silylamido) EuII complex, the [EuII(N{SiMePh2}2)2] SMM is described, providing an example of a europium complex exhibiting slow relaxation of its magnetization. This behavior is dominated by a thermally activated (Orbach-like) mechanism, with an effective energy barrier of approximately 8 K, determined by bulk magnetometry and electron paramagnetic resonance. Ab initio calculations confirm second-order spin-orbit coupling effects lead to non-negligible axial magnetic anisotropy, splitting the ground state multiplet into four Kramers doublets, thereby allowing for the observation of an Orbach-like relaxation at low temperatures.

Can Iron-Porphyrins Behave as Single-Molecule Magnets?

The study of magnetic properties, especially the magnetic anisotropy of iron-porphyrin complexes employing multiconfigurational methods, is quite challenging due to many strongly correlated electrons in nearly degenerate orbitals. However, a prerequisite for observing the magnetic anisotropy and slow magnetization relaxation, the zero-field splitting parameter, D, was experimentally observed decades ago for halide-based axially ligated penta-coordinate Fe(III)-porphyrins. In these complexes, the signs of D were reported mostly as positive; in a few cases, inconclusive signs of the D parameter were also mentioned. However, no ab initio calculations have been reported to shed light on this. Deciphering the electronic structure of these penta-coordinated complexes employing the complete active space self-consistent field method and N-electron valence second-order perturbation theory, we confirm the positive D values. However, a negative D value is highly desired to observe the single-molecule magnet properties without an external magnetic field, which we observed in the Fe(II)-porphyrin complexes with axial imidazole ligands instead of halide ligands. The detailed analysis of the multireference wave functions unravels the role of axial ligands in determining the sign and magnitude of the D parameters.

Oxygen-Donor Metalloligands Induce Slow Magnetization Relaxation in Zero Field for a Cobalt(II) Complex with {CoO4} Motif.

Most 3d metal-based single-molecule magnets (SMMs) use N-ligands or ligands with even softer donors to impart a particular coordination geometry and increase the zero-field splitting parameter |D|, while complexes with hard O-donor ligands showing slow magnetization relaxation are rare. Here, we report that a diamagnetic NiII complex of a tetradentate ligand featuring two N-heterocyclic carbene and two alkoxide-O donors, [LO,ONi], can serve as a {O,O'}-chelating metalloligand to give a trinuclear complex [(LO,ONi)Co(LO,ONi)](OTf)2 (2) with an elongated tetrahedral {CoIIO4} core, D = -74.3 cm-1, and a spin reversal barrier Ueff = 86.9 cm-1 in the absence of an external dc field. The influence of diamagnetic NiII on the electronic structure of the {CoO4} unit in comparison to [Co(OPh)4]2- (A) has been probed with multireference ab initio calculations. These reveal a contrapolarizing effect of the NiII, which forms stronger metal-alkoxide bonds than the central CoII, inducing a change in ligand field splitting and a 5-fold increase in the magnetic anisotropy in 2 compared to A, with an easy magnetization axis along the Ni-Co-Ni vector. This demonstrates a strategy to enhance the SMM properties of 3d metal complexes with hard O-donors by modulating the ligand field character via the coordination of diamagnetic ions and the benefit of robust metalloligands in that regard.

Bimetallic Synergy Enables Silole Insertion into THF and the Synthesis of Erbium Single-Molecule Magnets.

The potassium silole K2 [SiC4 -2,5-(SiMe3 )2 -3,4-Ph2 ] reacts with [M(η8 -COT)(THF)4 ][BPh4 ] (M=Er, Y; COT=cyclo-octatetraenyl) in THF to give products that feature unprecedented insertion of the nucleophilic silicon centre into a carbon-oxygen bond of THF. The structure of the major product, [(μ-η8 : η8 -COT)M(μ-L1 )K]∞ (1M ), consists of polymeric chains of sandwich complexes, where the spiro-bicyclic silapyran ligand [C4 H8 OSiC4 (SiMe3 )2 Ph2 ]2- (L1 ) coordinates to potassium via the oxygen. The minor product [(μ-η8 : η8 -COT)M(μ-L1 )K(THF)]2 (2M ) features coordination of the silapyran to the rare-earth metal. In forming 1M and 2M , silole insertion into THF only occurs in the presence of potassium and the rare-earth metal, highlighting the importance of bimetallic synergy. The lower nucleophilicity of germanium(II) leads to contrasting reactivity of the potassium germole K2 [GeC4 -2,5-(SiMe3 )2 -3,4-Me2 ] towards [M(η8 -COT)(THF)4 ][BPh4 ], with intact transfer of the germole occurring to give the coordination polymers [{η5 -GeC4 (SiMe3 )2 Me2 }M(η8 -COT)K]∞ (3M ). Despite the differences in reactivity induced by the group 14 heteroatom, the single-molecule magnet properties of 1Er , 2Er and 3Er are similar, with thermally activated relaxation occurring via the first-excited Kramers doublet, subject to effective energy barriers of 122, 80 and 91 cm-1 , respectively. Compound 1Er is also analysed by high-frequency dynamic magnetic susceptibility measurements up to 106 Hz.

The prediction of single-molecule magnet properties via deep learning.

This paper uses deep learning to present a proof-of-concept for data-driven chemistry in single-molecule magnets (SMMs). Previous discussions within SMM research have proposed links between molecular structures (crystal structures) and single-molecule magnetic properties; however, these have only interpreted the results. Therefore, this study introduces a data-driven approach to predict the properties of SMM structures using deep learning. The deep-learning model learns the structural features of the SMM molecules by extracting the single-molecule magnetic properties from the 3D coordinates presented in this paper. The model accurately determined whether a molecule was a single-molecule magnet, with an accuracy rate of approximately 70% in predicting the SMM properties. The deep-learning model found SMMs from 20 000 metal complexes extracted from the Cambridge Structural Database. Using deep-learning models for predicting SMM properties and guiding the design of novel molecules is promising.

Novel lanthanide complexes with quinoline-2-carboxylic acid: Structural variety and magnetism

By means of the reaction of lanthanide chlorides with quinaldic (quinoline-2-carboxylic, HQA) acid in an aqueous-ethanolic medium in the presence of pyridine, the following complexes were obtained: the known binuclear [Nd2(QA)6(H2O)6]·3H2O (1) one and the novel compounds built of binuclear dicationic and mononuclear anionic moieties [Ln2(QA)4(H2O)4]2+[Ln(QA)4(H2O)]ˉ2·2EtOH·6H2O (Ln = Gd (2), Dy (3), Er (4), Yb (5)), as well as the anionic mononuclear one, [Hpy2]+[Er(QA)4]ˉ·4H2O (6). The complexes 2–5 were characterized by dc and ac magnetic measurements. Complex 3 exhibits the properties of a single-molecule magnet (SMM) in a zero static field with remagnetization barrier (Δeff/kB) of 82 K, while the other complexes display the properties of field-induced SMMs with the Δeff/kB values of 24, 19, and 33 K for the complexes 2, 4, and 5, respectively.

Two-dimensional metal–organic nanosheets composed of single-molecule magnets: structural modulation and enhanced magnetism utilizing the steric hindrance effect

Tuning the bulkiness of the single-molecule magnet (SMM) alters the structures of SMM-nanosheets, which results in enhanced perpendicular magnetic anisotropy and SMM properties.

Apparently improved energy barrier of Dy(iii) SMMs by adopting the bridging bipyrimidine ligand

By strategically selecting appropriate ligands, we have designed mononuclear and dimeric DyIII complexes in order to gain valuable insights into the impact of magnetic coupling on the magnetic properties of single-molecule magnets (SMMs).

LnDOTA puppeteering: removing the water molecule and imposing tetragonal symmetry.

Complexes of lanthanide(iii) ions (Ln) with tetraazacyclododecane-N,N',N'',N'''-tetraacetate (DOTA) are a benchmark in the field of magnetism due to their well-investigated and sometimes surprising features. Ab initio calculations suggest that the ninth ligand, an axial water molecule, is key in defining the magnetic properties because it breaks the potential C4 symmetry of the resulting complexes. In this paper, we experimentally isolate the role of the water molecule by excluding it from the metal coordination sphere without altering the chemical structure of the ligand. Our complexes are therefore designed to be geometrically tetragonal and strict crystallographic symmetry is achieved by exploiting a combination of solution ionic strength and solid state packing effects. A thorough multitechnique approach has been used to unravel the electronic structure and magnetic anisotropy of the complexes. Moreover, the geometry enhancement allows us to predict, using only one angle obtained from the crystal structure, the ground state composition of all the studied derivatives (Ln = Tb to Yb). Therefore, these systems also provide an excellent platform to test the validity and limitations of the ab initio methods. Our combined experimental and theoretical investigation proves that the water molecule is indeed key in defining the magnetic anisotropy and the slow relaxation of these complexes.

The effect of second coordination sphere interactions on the magnetic anisotropy of transition metals.

In the study of mononuclear transition metal single molecule magnets (SMMs), extensive research has concentrated on identifying optimal coordination geometries around the central metal ion to enhance SMM properties. However, the role of non-covalent interactions in the second coordination sphere has been relatively underexplored. Here, we study the impact of non-covalent Cl⋯H interactions on the magnetic anisotropy of the central Co(II) ion in the distorted axially compressed octahedral complex CoCl2(tu)4 (1) (tu = SC(NH2)2). By performing cantilever torque magnetometry on 1, the orientation of the magnetic easy axis is found to deviate by almost 40° from the axial Co-Cl bond. Theoretical modelling on structural modifications of the structure of 1, quantifies how the distance between the Cl ligand and the nearest H-atom significantly influences the orientation of the magnetic easy axis and the D-value. Experimental chemical bonding analysis based on multipole modelling of synchrotron X-ray diffraction data on 1 reveal that the nearby H-atoms polarize the electron density of the Cl-ligands. This polarization results in reduced electron density at the axial positions on the Co octahedra, explaining the calculated increase in the magnitude of the D-value, when the H-atoms are moved away from Cl in silico. Topological analysis of theoretical electron densities on modified structures of 1 corroborates an increase in the electron density at the Co-Cl bond critical point, as the nearby H-atoms are moved further from Cl. These findings demonstrate the significant influence that non-covalent interactions have on the magnetic anisotropy of mononuclear transition metals and opens the possibility of utilizing these interactions in the design of transition metal based SMMs.

Understanding Single-Molecule Magnet properties of lanthanide complexes from 4f orbital splitting.

We present an approach for connecting the magnetic anisotropy of lanthanide mononuclear complexes with their f-orbital splitting for both idealized and real coordination environments. Our proposal is straightforward to apply and provides sensible estimations of the energy spacing of the ground multiplet for axial magnetic systems. This energy splitting controls Single-Molecule Magnet properties of lanthanide complexes, determining key parameters such as the demagnetization energy barrier (Ueff). Importantly, this approach is consistent with the current paradigm of oblate and prolate preferences for the distribution of the f-electron density, but delivers a finer description for ions belonging to the same group (e.g. the oblates TbIII and DyIII). The model provides simple explanations for some general trends observed experimentally (e.g. the low barriers for ErIII complexes in comparison to DyIII or the large barriers observed for cyclopentadienyl DyIII complexes in comparison with other ligands based on organometallic rings), contributing as a valuable tool to expand our description of ligand field effects in lanthanide-based SMMs.

Biosynthesis of JC-La2CoO4 magnetic nanoparticles explored in catalytic and SMMs properties

We have reported the synthesis of JC-La2CoO4 magnetic nanoparticles from Jatropha Curcas L. leaf extract in aqueous medium and potential application study in catalytic & Single Molecule Magnets (SMMs). Several techniques were used to investigate the structural, morphological, and elemental composition, particle size, optical properties, catalytic and magnetic properties by XRD, FTIR, SEM, EDAX, XPS, UV–visible and squid magnetic measurement. It was found that the crystallite sizes and grain sizes of JC-La2CoO4 NPs were 11.3 ± 1 and 24.1 ± 1 nm respectively and surface morphology of the nanoparticles looks spherical shape with good surface area. The band gap of JC-La2CoO4 was found to be 4.95 eV indicates good semiconductor in nature. XPS studies shows that La and Co present in + 3 and + 2 oxidation state respectively and suggest the composition formula is La2CoO4 with satisfied all the valency of metal ions. The photocatalytic efficiency of La2CoO4 shows good result against methylene blue (MB) compared to other dyes like MO, NO, RhB in presence of sunlight with rate constant 56.73 × 10–3 min-1 and completely degraded within 115 mints. The importance of JC-La2CoO4 has magnetic properties with antiferromagnetic coupling and SMMs properties with nature.

Slow Magnetization Relaxation in a Family of Triangular {CoIII 2 LnIII } Clusters: The Effect of Diamagnetic CoIII Ions on the LnIII Magnetic Dynamics.

The first use of the Schiff base chelate N-naphthalidene-o-aminophenol (naphH2 ) in Co/Ln chemistry has afforded a family of isostructural [CoIII 2 LnIII (OMe)2 (naph)2 (O2 CMe)3 (MeOH)2 ] (Ln=Tb, Dy and Er) complexes, revealing a rare {CoIII 2 Ln(μ3 -OMe)}8+ triangular core composed of two diamagnetic CoIII ions and a 4f-ion with slightly distorted square antiprismatic geometry. Alternating current (ac) magnetic susceptibility studies revealed that {Co2 Dy}, and its magnetic diluted analogue {Co2 Dy0.05 Y0.95 }, behave as mononuclear single-molecule magnets (SMMs) with similar energy barriers for the magnetization reversal, Ueff , of ~85-90 K. SMM properties were also detected for {Co2 Er}, with the compound exhibiting a Ueff of 18.7 K under an applied magnetic field of 800 Oe. To interpret the experimental magnetic results, ab initio CASSCF/RASSI-SO and DFT calculations were performed as a means of exploring the single-ion characteristics of LnIII ions and comprehend the role of the diamagnetic CoIII ions in the magnetization relaxation of the three heterometallic compounds.

Theoretical Magnetic Relaxation and Spin-Phonon Coupling Study in a Series of Molecular Engineering Designed Bridged Dysprosocenium Analogues.

A detailed computational study of hypothetical sandwich dysprosium double-decker complexes, bridged by various numbers of aliphatic linkers, was performed to evaluate the effect of the structural modifications on their ground-state magnetic sublevels and assess their potential as candidates for single-molecule magnets (SMMs). The molecular structures of seven complexes were optimized using the TPSSh functional, and the electronic structure and magnetic properties were investigated using the complete active space self-consistent field method (CASSCF). Estimates of the magnetic moment blocking barrier (Ueff) and blocking temperatures (TB) are reported. In addition, a new method based on computed derivatives of effective demagnetization barriers Ueff with respect to vibrational normal modes was introduced and applied to evaluate the impact of spin-phonon coupling on the SMM properties. On the basis of the computed parameters, we have identified promising candidates with properties superior to those of the existing single-molecule magnets.