Assembling Ln(III) clusters by capturing and fixing CO2 from the air is a unique and eco-friendly approach to yielding multinuclear single-molecule magnets and magnetocaloric molecular materials. However, the conditions or factors required to facilitate this process are still unclear. When synthesizing Ln(III) complexes using a hydrazone Schiff base (H2Lschiff) condensed from o-vanillin and 3-aminopyrazine-2-carbohydrazide, LiOH plays a decisive role in the formation of [Dy8(Lschiff)8(CO3)4(H2O)8]·4DMA·4H2O (1) by capturing and fixing CO2 from the air, as using Et3N under the same conditions only yields a normal product, [Dy2(Lschiff)2(DMA)3(H2O)3](CF3SO3)2·3DMA·H2O (2). Either 1 or 2 exhibits intramolecular ferromagnetic interactions, and both perform as good zero-field single-molecule magnets (SMMs). Furthermore, an analog of 1, complex [Gd8(Lschiff)8(CO3)4(H2O)8]·4DMA·4H2O (3), was obtained using a synthesis method similar to that of 1, exhibiting a good magnetocaloric effect. Therefore, choosing the appropriate alkali is a necessary prerequisite for fixing CO2 from the air to assemble polynuclear Ln(III) SMMs and magnetocaloric molecular materials.

Tunable quantum states and long spin-relaxation times are crucial requirements for the application of single-molecule magnets (SMMs) in spintronics and quantum information technologies. Here, we take metallocenes (MCp2) with various transition metal centers, together with ferroelectric In2Se3, as a model to explore the feasibility of ferroelectric control over the quantum states of SMMs through systematic first-principles calculations. The calculated results demonstrate that the quantum state of MCp2 can be effectively modulated by turning the polarization direction of the In2Se3 substrate. Particularly, for TaCp2, the magnetic anisotropy energy can be regulated from 2.82 to 16.67 meV. These findings provide fundamental insights into the ferroelectric manipulation of single spin.

Cu(II) coordination compounds have ½ spin system; thus, they cannot exhibit single-molecule magnet behavior; however, under a static magnetic field, slow magnetic relaxation can occur. Such compounds are interesting because this type of magnetism is related to spin qubits. Nevertheless, examples of this type of Cu(II) compounds are still rare, and hence the search for novel synthetic approaches becomes a necessity. In this study we have presented the first example of photoreactive Cu(II) coordination compound exhibiting field induced slow magnetic relaxation. The introduction of an able to [2+2] photocyclization coumarin fragment resulted in the possibility to convert Cu(II) system, showing field induced slow magnetic relaxation at 16 K, to another one also exhibiting slow relaxation however shifted below 5 K. Light induced [2+2] cyclization occurs in the studied system practically quantitatively which opened the way to combine relaxation pathways in the one material via controllable partial photoconversion. This approach, to date unexplored, resulted in obtaining a half-photoconverted system exhibiting the characteristics close to the pre-conversion and post-conversion systems. Thus, controlled photoconversion has become a convenient way to modulate properties without having to synthesize compounds from their initially chemically modified building blocks.

Both pentagonal bipyramidal (PB) and hexagonal bipyramidal (HB) mononuclear dysprosium (Dy) complexes are highly efficient in generating a stable single-molecule magnet (SMM) with strong axial magnetic anisotropy. Thus, they are suitable for constituting a platform for future development of stable high-performance SMMs. However, we still lack a detailed theoretical study of both PB and HB Dy complexes. To cover this shortage, we provide here a combined ab initio calculation and feature attribution analysis of 12 PB and 12 HB DyIII complexes. Compared to PB complexes, HB ones usually have slower thermally activated relaxation but faster quantum tunneling of magnetization. This may lead to a lower SMM performance of HB complexes even though their effective barriers are usually higher. The importance of features, which are more sensitive to the direction rather than the distance or electric charge of ligating atoms, supports the significant role of covalency, which is more sensitive to direction than electrostatics. The effect of covalency is quantified by the change from full structures to various charge-embedded model structures. Total covalency is detrimental to SMM performance, and its effect can be huge. This comes from the fact that the covalency from equatorial ligands is destructive and quite stronger than the constructive covalency from axial ligands. The constructive nature of axial covalency comes from its destabilization of 4f0 and 4f±1 orbitals of the central DyIII ion. However, equatorial covalency is more efficient in destabilizing 4f±2 and 4f±3 orbitals, which disfavors SMM performance.

We report the synthesis, crystal structure, and magnetic properties of the muffin-shaped complex [Er(PPTMP)2(H2O)][OTf]3 (PPTMP = (4-(6-(1,10-phenanthrolin-2-yl)pyridin-2-yl)-1H-1,2,3-triazol-1-yl)methyl pivalate) (1). Complex 1 is shown to exhibit field-induced slow relaxation of the magnetization at B = 0.1 T via two distinct relaxation paths. Using tunable high-frequency/high-field electron paramagnetic resonance spectroscopy, we experimentally determine the effective g-factors and zero field splittings (ZFS) of the two energetically lowest Kramers doublets (KD). Our data reveal that the distorted muffin-shaped ligand field favors an m ≃ ±9/2 magnetic ground state, while the main contribution to the first excited KD at Δ1→2 = 780(5) GHz is suggested to be m ≃ ±5/2. The ground state g-tensor has generally an axial form but hosts significant transversal components, which we conclude to be the source of single molecule magnet (SMM)-silent behavior in zero field. Our findings are backed up by ab initio spin-orbit configuration interaction calculations showing excellent agreement with the experimental data and, in particular, highlight that the counterions should be included in the numerical modeling of the crystalline structure.

Mixed-valence complexes featuring lanthanide-lanthanide bonding have recently been shown to act as single-molecule magnets with unprecedented operating temperatures and magnetic coercivities. Here, we present the synthesis and detailed examination of the electronic structure, bonding, and magnetic properties of mixed-valence trinuclear clusters (C5iPr5)3Ln3H3I2 (Ln = Tb, Dy, Ho, Er, and Tm). Near-infrared and X-ray absorption spectra, together with computational results, confirm these clusters possess a three-center, one-electron σ bond. This metal-metal bonding leads to strong intermetal exchange coupling, resulting in magnetic behaviors that starkly contrast with typical multinuclear lanthanide complexes. Notably, structural, spectroscopic, and computational studies of the thulium cluster reveal valence delocalization through a bonding orbital of 5d-parentage between the three Tm centers. This observation represents the first example of a nontraditional electronic structure for thulium involving 5d rather than 4f orbitals. Magnetic analysis reveals a complex interplay between single-ion magnetic anisotropy and ferromagnetic exchange, governing the overall magnetic anisotropy of these clusters. Magnetic susceptibility measurements for Ln = Tb-Er indicate thermally well-isolated high-moment ground states arising from strong magnetic coupling, although the maximum values are lower than those expected for complete parallel alignment of the σ and 4f electrons. Computational analyses suggest that collinear alignment of the local anisotropy axes results in out-of-plane anisotropy for Ln = Er and Tm, whereas noncollinear alignment induces in-plane anisotropy for Ln = Tb, Dy, leading to distinct magnetic relaxation properties. Together, the results highlight the diverse magnetic behaviors that can be realized through lanthanide-lanthanide bonding and outline a synthetic path forward toward maximizing the magnetic anisotropy in f-element clusters.

In molecular spintronics, achieving precise control over the spin polarization direction of transported electrons at the single-molecule level remains a great challenge. This study addresses this challenge by leveraging the unique electronic structure of bipolar magnetic molecules (BMMs). By performing density functional theory (DFT) calculations, we designed and screened a series of transition metal complexes, identifying Cr(II)(BBM)2 (where BBM is the 2,2'-bibenzoimidazole anion) as a promising BMM candidate. Combining DFT with the non-equilibrium Green's function (NEGF) formalism, spin-polarized quantum transport calculations were carried out on a molecular junction where Cr(II)(BBM)2 was coupled to graphite electrodes. Our results demonstrate that the application of an external gate voltage enables reversible switching of the spin transport direction. A gate voltage of -5 V yields a 100% spin-polarized current in the spin-up channel. Conversely, a small positive gate voltage of +0.05 V results in a completely polarized spin-down current. This gate-controlled spin channel switching, achieved through rational molecular design, underscores the potential of BMMs as fundamental components for future ultra-dense, low-power spintronic devices.

Electrical detection of magnetization switching in single-molecule magnets

In endohedral fullerenes otherwise unstable atomic clusters can be stabilized. Here we investigate the electronic and magnetic properties of the dimetallic endohedral fullerene CeTi@C 80 , a molecular system encapsulating nominally trivalent cations of Ce and Ti within a C 80 carbon cage. Using low temperature magnetometry and temperature-dependent X-ray Absorption Spectroscopy (XAS) at the Ce M 4 , 5 -edge, we explore the magnetism and the orientation of the Ce–Ti endohedral unit. The magnetization measurements indicate ”tender” single-molecule magnetism with small hysteresis and a 3.3 μ B magnetic moment. The measured XA spectra of drop-cast molecules can be simulated with a ligand field of a didipole that consists of a C–Ti and an opposite Ce–C dipoles. They confirm trivalent Ce with a J z =5/2 ground state and random distribution of the Ce–Ti axes. Temperature-dependent XAS below room temperature shows minimal spectral change, indicating a thermally robust ground-state. These findings establish CeTi@C 80 as a stable electric and magnetic didipole single molecule magnet. • Single molecule magnetism of CeTi@C 80 above 2 K. • High J z ground state of Ce at low temperatures as established by magnetometry. • Stable Ce 4f J z = 5 / 2 ground state up to room temperature and isotropic Ce–Ti axis distribution in multilayers as established by Ce M 4 , 5 -edge X-ray Absorption Spectroscopy.

Synthesis, structure, and single-molecule magnet property of a mixed cyanide-oxo-bridged {FeIII2FeII2} complex featuring pentagonal bipyramidal Fe(II) centers

Single-molecule magnets (SMMs) are molecules that can function as nanoscale magnets with potential use as magnetic memory bits. While SMMs can retain magnetization at low temperatures, characterizing them on surfaces and at room temperature remains challenging and requires specialized nanoscale techniques. Here, we use single nitrogen-vacancy (NV) centers in diamond as a highly sensitive, broadband magnetic field sensor to detect the magnetic noise of cobalt-based SMMs deposited on a diamond surface. We measured the NV relaxation and decoherence times at 296 K and at 5-8 K, observing a significant influence of the SMMs on them. From this, we infer the SMMs' magnetic noise spectral density (NSD) and underlying magnetic properties. Moreover, we observe the effect of an applied magnetic field on the SMMs' NSD at low temperatures. The method provides nanoscale sensitivity for characterizing SMMs under realistic conditions relevant to their use as surface-bound memory units.

The state of the art in single-molecule magnet (SMM) design is dominated by charged dysprosium sandwich complexes with mono- or dianionic π-ligands, which exhibit some of the highest open-loop magnetic hysteresis temperatures (TH), the highest 100 s blocking temperatures (TB100), and some of the largest barriers to magnetic reversal (Ueff). Architectures that leverage more charge-dense ligands, such as amides or alkoxides, with axial coordination and weak equatorial interactions can generate larger crystal fields (CFs), and hence larger Ueff values; however, this is often not accompanied by correspondingly high TH or TB100 values. Here, we report a four-coordinate dysprosium(III) SMM, [Dy{Me2Si(NSiiPr3)2}2{K(toluene)2}]n (1Dy), with charge-dense amide donors but a coordination environment that is between axial and tetrahedral in structure. Nevertheless, 1Dy displays open-loop magnetic hysteresis up to 31 K using sweep rates of 22 Oe s-1. The coercive field (HC) is 1.65 T at 1.8 K, and TB100 = 10.4 K. Ab initio calculations show the four-coordinate geometry imparts a strong axial CF as the 6H15/2 spin-orbit multiplet is split over 1958 K (1361 cm-1). The experimental Ueff (742 K, 516 cm-1) is smaller and resides near the energy of the third excited Kramers doublet. Ab initio spin dynamics calculations show that the fitted barrier height at high T (>45 K) is 559 cm-1. Non-Kramers ion analogues 1Tb and 1Ho show waist-restricted hysteresis and short relaxation times at all temperatures. The magnetic properties of 1Dy place it highly among monometallic lanthanide SMMs using an alternative design strategy, which is synthetically simple and may be further refined.

Single-molecule magnets represent promising materials due to their stable magnetic states and long relaxation times. Precise engineering of their quantum properties is of importance to realize advanced electronic devices, such as high-density data storage, quantum computing, and spintronics. Here, we investigate the spin state of nickelocene (NiCp2) and cobaltocene (CoCp2) molecules manipulated by Br atoms. With a combination of scanning tunneling microscopy and density functional theory calculations, we reveal that the high electronegativity of Br atoms significantly changes the magnetic properties of both NiCp2 and CoCp2. For NiCp2, the spin-state transition from its intrinsic S = 1 to S = 1/2 occurs when the Br atoms underlying the molecule consist of more than five atoms. The spin state is further shifted to S = 0 by approaching a Br-terminated tip toward the molecule. In contrast, a strong hybridization between CoCp2 and Br atoms leads to a complete quenching of its spin moment. This strategy for tuning molecular spin states provides a promising route toward the scalable design of molecular spintronic devices.

The loss of magnetic memory in single-molecule magnets (SMMs) is caused by the coupling of molecular vibrations to spin states, which plays a significant role in magnetic relaxation processes. Gaining direct evidence of vibronic coupling using experimental techniques is critical to understanding and controlling this phenomenon. Most studies focus on assessing the spin-phonon coupling in SMMs to help control this relaxation; herein we gain insight by comparing the SMM [Dy(OPCy3)2(H2O)5][CF3SO3]3.2(OPCy3)to the non-SMM [Dy{N(SiMe3)2}3]through collection of far-infrared magnetospectroscopy (FIRMS) spectra and validation with ab initio calculations. Single-crystal measurements display a prominent feature in the spectra at 340 cm-1, corresponding to an electronic excitation which varies depending on the direction of external magnetic field applied. These findings demonstrate the complicated effect of magnetic anisotropy on the vibronic coupling in SMMs and demonstrate the power of FIRMS to study these effects.

Molecular nanomagnets have garnered significant attention in recent years thanks to their unique potential in quantum information processing as molecular qudits and in high-density memory encoding as single-molecule magnets. However, fully unlocking the potential of these systems requires a comprehensive understanding of the interplay between the various mechanisms that govern their relaxation dynamics, which remains a noncompletely understood phenomenon. In this work, we employ a cost-effective semi- approach to model the magnetization relaxation dynamics in a testbed Dy-based single-molecule magnet and determine the effects of applied external pressure on the interplay between various mechanisms, such as coupling with molecular vibrations and quantum tunneling. phonon calculations are validated by direct comparison with inelastic neutron scattering experiments, which are used for the first time to investigate pressure-induced modifications of phonons and vibrations in a molecular nanomagnet. The combination of our theoretical approach with different experimental techniques allows us to predict an overall acceleration of the relaxation dynamics under pressure, disentangling the role of different ingredients, such as crystal field axiality and phonons.

Ytterbium-(III) complexes have attracted growing interest due to their unique magnetic properties and potential applications in molecular magnetism. From this perspective, the synthesis, structural characterization, and magnetic and theoretical studies of a new mononuclear Yb-(III) complex, [YbI2(OPPh3)4]-(I3) (1), are reported. Compound 1 features a six-coordinate Yb-(III) ion that adopts a distorted octahedral geometry with two axial iodide ions (I-) and four equatorial triphenylphosphine oxide (Ph3PO) ligands. Magnetic studies reveal that complex 1 exhibits entirely visible out-of-phase signals below 7 K under an 800 Oe applied dc field and slow magnetic relaxation, consistent with field-induced single-molecule magnetism behavior. Ab initio calculations rationalize the experimental magnetic dynamics, suggesting the dominance of the Raman mechanism in 1 over the Orbach relaxation pathway. The LoProp charges study elucidates the contribution of the equatorial ligand's oxygen atoms and the polarizability of the negatively charged axial iodide ligands, which enhances the magnetic anisotropy of the prolate Yb-(III) ion, resulting in significant crystal-field splitting.

The intrinsic shielding of lanthanide 4f orbitals leads to weak magnetic exchange, a fundamental limitation that can be addressed by using radical-bridged ligands. In this work, we employed the electron-deficient ligand 3,6-bis(2,2'-bipyridyl)-1,2,4,5-tetrazine (bbpytz) and prepared a series of di- and trinuclear lanthanide complexes by intentionally controlling the stoichiometry of bbpytz and Ln(acac)3. This approach yielded the dinuclear complexes [LnIII2(bbpytz•-)(μ2-OH)(acac)4] (Ln = Dy, 1; Tb, 2) and trinuclear complexes [LnIII3(bbpytz•-)(μ2-OH)(acac)7]·2MeCN (Ln = Dy, 3; Tb, 4; Gd, 5; Y, 6), in which the reduced tetrazine ligand (bbpytz•-) serves as both a bridging and capping radical ligand. Magnetic studies reveal antiferromagnetic coupling between the radical and LnIII centers, with coupling constant (-2J formalism) of -3.3 (1), -6.0 (3), and -3.8 cm-1 (5). Ab initio calculations support strong axial anisotropy for the DyIII ions and demonstrate a near-parallel alignment of magnetic easy axes. As a result, dysprosium complexes 1 and 3 exhibit slow magnetic relaxation and function as zero-field single-molecule magnets (SMMs), with effective energy barriers of 18.8 and 19.8 K, respectively. This study underscores the dual role of tetrazine radicals in enabling both strong magnetic exchange and control over magnetic anisotropy for the design of high-performance SMMs.

Single-molecule magnets (SMMs) exhibit magnetic hysteresis below a blocking temperature (TB), offering potential in high-density data storage and quantum computing. Practical applications, however, are limited by low TB, insufficient magnetic anisotropy, molecular instability, quantum tunneling of magnetization (QTM), and integration challenges. Traditional progress relied on serendipitous synthesis, but computational approaches like DFT and ab initio CASSCF have revealed structure-property relationships, enabling breakthroughs in lanthanide-based SMMs with TB approaching the liquid nitrogen temperature. Here, we explore oriented external electric fields (OEEFs) as a tool to address these challenges. Using DFT, DFT-based response methods, and CASSCF/RASSI-SO calculations, we systematically studied over 100 Dy(III) toy models with varying coordination numbers from 1 to 8 under electric fields and extended this to 35 Dy(III) SMMs from the literature. We establish a framework to select molecules and optimal field directions for probing under OEEFs. Our results show that OEEFs can effectively manipulate Dy(III) anisotropy, QTM, crystal field effects, and local symmetry, and can toggle SMMs on/off while enhancing magnetization reversal barriers by up to 6-fold. Additionally, OEEFs can modulate geometric isomerism, offering a strategy to fine-tune SMM properties. These findings provide guidelines for optimizing molecular magnets and open avenues for their application in quantum technologies and information storage.

ConspectusSingle-molecule magnets (SMMs), particularly those based on lanthanide ions, have emerged as a revolutionary class of molecular nanomaterials with potential applications in quantum computing, high-density information storage, and spintronic devices. The key to unlocking their full potential lies in the precise engineering of ligand fields to control the magnetic anisotropy and slow magnetic relaxation dynamics. This Account presents our group's systematic investigations into advanced coordination geometry regulation strategies and organometallic ligand design for optimizing the performance of lanthanide SMMs, with particular focus on establishing clear magneto-structural correlations and developing innovative coordination approaches.Central to our design philosophy is the fundamental understanding that for Dy(III) and Tb(III) ions with oblate electron density strong axial ligand fields coupled with minimized equatorial interactions are crucial for achieving maximum magnetic axiality. Our research has developed two synergistic strategies to realize this ideal coordination environment: (1) pseudo-two-coordinate model with symmetry control and (2) conjugated chelating organometallic ligand engineering. In the first approach, we have constructed a series of Werner-type complexes with well-defined local symmetries (D4h, D5h, D6h, etc.), creating model systems that feature weak equatorial crystal fields while maintaining strong axial ones. These carefully designed architectures have yielded exceptionally large energy barriers for magnetization reversal with some complexes approaching those of state-of-the-art SMMs. Beyond symmetry considerations, we have demonstrated how subtle modifications of the geometry can fine-tune crystal field parameters, while the introduction of rigid axial ligands effectively suppresses quantum tunneling of magnetization and Raman relaxation processes. This dual control strategy has led to significant improvements in magnetic blocking temperatures of the pseudo-two-coordinate system. Our second strategy involves the development of novel π-delocalized organometallic ligands, including carboranyl, amidinate, and guanidinate systems. These ligands offer advantages comparable to those of cyclopentadienyl derivatives. For instance, carboranyl anions provide very strong ligand fields due to their unique electronic structures, while amidinate ligands exhibit a labile chelating capability to stabilize Dy(II) and Tb(II) ions, opening new frontiers in nontraditional low-valent lanthanide chemistry as well as magnetochemistry. These works highlight the importance of coordination geometry and the ligand field in engineering high-performance SMMs and provide insights into the magneto-structural correlations. While challenges remain in truly understanding the relaxation mechanism and further improving blocking temperatures, these strategies offer clear pathways for advancing lanthanide-based SMMs.

We report on the synthesis of the lanthanide-containing17-tungsto-1-phosphates[Ln­(P­(H4)­W17O61)2]19– (Ln = La3+, Ce3+, Eu3+, Gd3+, Yb3+, Lu3+, Y3+), comprising a lanthanide ion connecting two [P­(H4)­W17O61]11– units in a syn-configuration. The compounds were characterized in the solid stateby IR, powder XRD, and TGA, and in solution by 31P and 183W NMR. Alternating current magnetic susceptibility investigationsrevealed the Ce3+ and Yb3+ analogues to be single-moleculemagnets (SMM), which was further corroborated by sub-kelvin temperatureμSQUID studies. For the Eu3+ analogue, we have observeda strong 5D0 → 7FJ (J = 0–4) emission alongwith a weaker 5DJ (J = 1, 2, or 3) → 7FJ emission arising from higher excited state manifolds, uponexcitation via the 7F0 → 5L6 transition at 395 nm. Analysis of the steady-stateand time-resolved data suggests a distorted square-antiprismatic coordinationgeometry around the Eu3+ center. The presence of watermolecules residing in the outer coordination sphere appears to decreasethe intrinsic quantum yield (φEu) by providing O–Hoscillators as a nonradiative relaxation channel. The observed branchingratio of about 41% for the 5D0 → 7F4 transition highlights that [Eu­(P­(H4)­W17O61)2]19– exhibitsa pronounced 5D0 → 7F4 emission.