Influence of Guest Exchange on the Magnetization Dynamics of Dilanthanide Single-Molecule-Magnet Nodes within a Metal-Organic Framework

The rise of 3-d single-ion magnets in molecular magnetism: towards materials from molecules?

Single-molecule magnets (SMMs) that contain one spin centre (so-called single-ion magnets) theoretically represent the smallest possible unit for spin-based electronic devices. The realisation of this and related technologies, depends on first being able to design systems with sufficiently large energy barriers to magnetisation reversal, Ueff, and secondly, on being able to organise these molecules into addressable arrays. In recent years, significant progress has been made towards the former goal - principally as a result of efforts which have been directed towards studying complexes based on highly anisotropic lanthanide ions, such as Tb(iii) and Dy(iii). Since 2013 however, and the remarkable report by Long and co-workers of a linear Fe(i) system exhibiting Ueff = 325 K, single-ion systems of transition metals have undergone something of a renaissance in the literature. Not only do they have important lessons to teach us about anisotropy and relaxation dynamics in the quest to enhance Ueff, the ability to create strongly coupled spin systems potentially offers access to a whole of host of 1, 2 and 3-dimensional materials with interesting structural and physical properties. This perspective summarises recent progress in this rapidly expanding sub-genre of molecular magnetism from the viewpoint of the synthetic chemist, with a particular focus on the lessons that have so far been learned from single-ion magnets of the d-block, and, the future research directions which we feel are likely to emerge in the coming years.

Lanthanide dinuclear complexes constructed from mixed oxygen-donor ligands: the effect of substituent positions of the neutral ligand on the magnetic dynamics in Dy analogues

Two series of lanthanide dinuclear complexes with the general formulae, [Ln(n-PNO)(Bza)3(H2O)] {Bza = benzoic acid; n = 3, n-PNO = 3-picoline N-oxide, Dy(1) and Er(2); and n = 4, n-PNO = 4-picoline N-oxide, Nd(3), Eu(4), Gd(5), Tb(6), Dy(7), Er(8) and Y(9)} have been successfully synthesized by the hydrothermal method. Single-crystal X-ray diffraction experiments illustrate that the two series of compounds possess similar carboxylic ligand-bridged dinuclear structure and coordination geometry around the lanthanide ions despite the different methyl-substituent positions on the neutral ligand. Comparative studies of the Dy analogues in the static-field measurements reveal only a little difference with a small butterfly-shaped opening for complex 1 and a close hysteresis loop for 7 at 2.0 K. However, systematic investigations of the alternating-current (ac) measurements indicate that the different substituent positions of the picoline N-oxide ligand have a significant effect on the magnetic relaxation dynamics. A more substantial suppression of the quantum tunnelling of magnetization (QTM) effect and pronounced slow magnetic relaxation were observed in complex 7 as compared to 1 under both zero and a 1 kOe static field.

Magneto-structural correlations in arsenic- and selenium-ligated dysprosium single-molecule magnets

The structures and magnetic properties of the arsenic- and selenium-ligated dysprosium single-molecule magnets (SMMs) [Cp'3Dy(AsH2Mes)] (3-Dy), [(η5-Cp'2Dy){μ-As(H)Mes}]3 (4-Dy), [Li(thf)4]2[(η5-Cp'2Dy)3(μ3-AsMes)3Li] ([Li(thf)4]2[5-Dy]), and [(η5-Cp'2Dy){μ-SeMes}]3 (6-Dy) are described. The arsenic-ligated complexes 4-Dy and 5-Dy are the first SMMs to feature ligands with metalloid elements as the donor atoms. The arsenide-ligated complex 4-Dy and the selenolate-ligated complex 6-Dy show large anisotropy barriers in the region of 250 cm-1 in zero d.c. field, increasing to 300 cm-1 upon 5% magnetic dilution. Theoretical studies reveal that thermal relaxation in these SMMs occurs via the second-excited Kramers' doublet. In contrast, the arsinidene-ligated SMM 5-Dy gives a much smaller barrier of 23 cm-1, increasing to 35 cm-1 upon dilution. The field-dependence of the magnetization for 4-Dy and 5-Dy at 1.8 K show unusual plateaus around 10 kOe, which is due to the dominance of arsenic-mediated exchange over the dipolar exchange. The effects of the exchange interactions are more pronounced in 5-Dy, which is a consequence of a small but significant increase in the covalent contribution to the predominantly ionic dysprosium-arsenic bonds. Whereas the magnetically non-dilute dysprosium SMMs show only very narrow magnetization versus field hysteresis loops at 1.8 K, the impact of magnetic dilution is dramatic, with butterfly-shaped loops being observed up to 5.4 K in the case of 4-Dy. Our findings suggest that ligands with heavier p-block element donor atoms have considerable potential to be developed more widely for applications in molecular magnetism.

Guest-dependent single-ion magnet behaviour in a cobalt(ii) metal-organic framework

Single-ion magnets (SIMs) are the smallest possible magnetic devices for potential applications in quantum computing and high-density information storage. Both, their addressing in surfaces and their organization in metal-organic frameworks (MOFs) are thus current challenges in molecular chemistry. Here we report a two-dimensional 2D MOF with a square grid topology built from cobalt(ii) SIMs as nodes and long rod-like aromatic bipyridine ligands as linkers, and exhibiting large square channels capable to host a large number of different guest molecules. The organization of the cobalt(ii) nodes in the square layers improves the magnetic properties by minimizing the intermolecular interactions between the cobalt(ii) centres. Moreover, the SIM behaviour was found to be dependent on the nature of the aromatic guest molecules. The whole process could be followed by single-crystal X-ray diffraction, providing comprehensive evidence of the putative role of the solvent guest molecules that leave a "fingerprint" on the 2D structures and thus, on the cobalt environment.

Two-step warming solvothermal syntheses, luminescence and slow magnetic relaxation of isostructural dense LnMOFs based on nanoscale 3-connected linkers

Two isostructural 3D dense LnMOFs exhibiting either photoluminescence or slow magnetic relaxation are assembled under two-step warming solvothermal conditions.

Hydrous salts of 1-aminoethylidenediphosphonic acid and piperazidine: temperature induced reversible structural transformation in a humid environment

A series of hydrous salts constructed using AEDPH₄ and piperazidine (pip) were synthesized and structurally characterized. A reversible structural transformation circle is observed in single crystals of compounds 1–3.

Near-infrared luminescence and SMM behaviors of a family of dinuclear lanthanide 8-quinolinolate complexes

Herein we report the near-infrared luminescence properties and SMM behaviors of five new lanthanide complexes based on 8-hydroxyquinoline and dibenzoylmethanate ligands.

HCl chemisorption-induced drastic magneto-structural transformation in a layered cobalt–phosphonotriazolate coordination polymer

A stimuli-responsive magnetic coordination polymer was synthesized, which shows an antiferro- to ferromagnetic response to HCl vapour in a crystal-to-crystal transformation.

Constraining the coordination geometries of lanthanide centers and magnetic building blocks in frameworks: a new strategy for molecular nanomagnets

The study of molecular nanomagnets can be expanded to a new platform of metal–organic frameworks.

A 3D MOF constructed from dysprosium(iii) oxalate and capping ligands: ferromagnetic coupling and field-induced two-step magnetic relaxation

Field-induced two-step magnetic relaxation was observed in the first ferromagnetic 3D lanthanide(iii) oxalate framework with a capping ligand.

New sandwich-type lanthanide complexes based on closed-macrocyclic Schiff base and phthalocyanine molecules

Two new sandwich-type lanthanide complexes simultaneously containing closed-macrocyclic Schiff base and phthalocyanine molecules were synthesized and structurally characterized. The magnetic studies reveal the corresponding dysprosium complex behaves as a typical SMM.

Single-molecule magnet behavior in an octanuclear dysprosium(iii) aggregate inherited from helical triangular Dy3 SMM-building blocks

A novel supramolecular octanuclear dysprosium(iii) cluster coupling two original helical Dy₃ SMM-building blocks is isolated and shows typical SMM behavior under zero dc field inherited from its Dy₃ helical precursor.

Coherence and organisation in lanthanoid complexes: from single ion magnets to spin qubits

Molecular magnetism is reaching a degree of development that will allow for the rational design of sophisticated systems.

Correlation between structural, physical and chemical properties of three new tetranuclear NiII clusters

The structural alteration in investigated tetranuclear Ni^II clusters induced only by solvent exchange resulted in significant changes in their physical and chemical properties.

Lanthanoid single-ion magnets with the LnN10 coordination geometry

Two unprecedented single-ion magnets (SIMs) with the homoatomic LnN₁₀ coordination geometry were reported, where the central Ln (Ln = Dy^III or Er^III) ion is interlocked by two pentadentate ligands (N5) affording a low symmetric polyhedron. Studies of the dynamic magnetic behaviours show an effective energy of 79(4) K for [Dy(N5)₂]³⁺ and 59(4) K for [Er(N5)₂]³⁺, respectively.

Metal-Organic Frameworks as Platforms for the Controlled Nanostructuring of Single-Molecule Magnets

The prototypical single-molecule magnet (SMM) molecule [Mn12O12(O2CCH3)16(OH2)4] was incorporated under mild conditions into a highly porous metal-organic framework (MOF) matrix as a proof of principle for controlled nanostructuring of SMMs. Four independent experiments revealed that the SMM clusters were successfully loaded in the MOF pores, namely synchrotron-based powder diffraction, physisorption analysis, and in-depth magnetic and thermal analyses. The results provide incontrovertible evidence that the magnetic composite, SMM@MOF, combines key SMM properties with the functional properties of MOFs. Most importantly, the incorporated SMMs exhibit a significantly enhanced thermal stability with SMM loading advantageously occurring at the periphery of the bulk MOF crystals with only a single SMM molecule isolated in the transverse direction of the pores.

A Dy2 single-molecule magnet with benzoate anions and phenol-O− bridging groups

A Dy₂ single-molecule magnet, namely [Dy₂(H₃L)₂(PhCOO)₄]·4H₂O (1), was obtained from the reaction of Dy(PhCOO)₃ with 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide (H₄L).