Rebecca J. Holmberg

Supramolecular Assembly of Molecular Rare-Earth–3,5-Dichlorobenzoic Acid–2,2′:6′,2″-Terpyridine Materials: Structural Systematics, Luminescence Properties, and Magnetic Behavior

The syntheses and crystal structures of 16 new rare-earth (RE = La(3+)-Y(3+))-3,5-dichlorobenzoic acid-terpyridine molecular materials characterized via single-crystal and powder X-ray diffraction are reported. These 16 complexes consist of four unique structure types ranging from molecular dimers (La(3+) and Ce(3+)) to tetramers (Pr(3+)-Y(3+)) as one moves across the RE(3+) series. This structural evolution is accompanied by subsequent changes in modes of supramolecular assembly (halogen bonding, halogen-π, halogen-halogen, and π-π interactions). Solid-state visible and near-infrared lifetime measurements were performed on complexes 6 (Sm(3+)), 7 (Eu(3+)), 9 (Tb(3+)), 10 (Dy(3+)), 11 (Ho(3+)), 12 (Er(3+)), and 14 (Yb(3+)), and characteristic emission was observed for all complexes except 11. Lifetime data for 11, 12, and 14 suggest sensitization by the terpy antenna does occur in near-infrared systems, although not as efficiently as in the visible region. Additionally, direct current magnetic susceptibility measurements were taken for complexes 10 (Dy(3+)) and 12 (Er(3+)) and showed dominant ferromagnetic behavior.

Adhering magnetic molecules to surfaces

The field of molecular magnetism has a strong focus on the design and improvement of magnetic molecules towards their potential application in molecular electronics; spintronics, quantum computing, information storage, etc. However, despite the growth and expansion of the field, there are still few researchers exploring the fundamental concern of their successful adhesion and interaction with surface structures, while maintaining their inherently desirable magnetic properties. Thus, in this review we aim to present an overview of the work that has been performed on attaching and studying Single-Molecule Magnets (SMMs) on various surfaces, with an emphasis on molecular design for surface interaction and on the magnetic properties before and after adhesion occurs.

Terminal solvent effects on the anisotropy barriers of Dy2 systems

A family of three dinuclear dysprosium complexes have been successfully synthesized and studied in terms of their magnetic properties. Complexes 1 and 2 share the formula [Dy2(ovph)2Cl2(solvent)2], where H2ovph = pyridine-2-carboxylic acid [(2-hydroxy-3-methoxyphenyl)methylene] hydrazide, and solvent = DMF (1), i-PrOH (2), while complex 3, [Dy2(ovph)2Cl2(H2O)3(EtOH)], exhibits differences in terms of the identity and number of coordinated solvent molecules. Thus, we investigate the impact of terminally bonded solvent molecules on the slow relaxation dynamics of {Dy2} SMMs, a parameter which can sometimes be overlooked in the quest to attain higher energy barriers. Notably, the exchange of DMF for i-PrOH, both of which coordinate through a single oxygen atom, results in a near 2-fold increase in Ueff, from 58 to 98 K, for 1 and 2, respectively.

Paramagnetic Nanocrystals: Remarkable Lanthanide-Doped Nanoparticles with Varied Shape, Size, and Composition.

Magnetic nanoparticles have been developed in recent years with applications in unique and crucial areas such as biomedicine, data storage, environmental remediation, catalysis, and so forth. NaYF4 nanoparticles were synthesized and isolated with lanthanide dopant percentages, confirmed by ICP-OES measurements, of Er, Yb, Tb, Gd, and Dy that were in agreement with the targeted ratios. SEM images showed a distinct variation in particle size and shape with dopant type and percentage. HRTEM and XRD studies confirmed the particles to be crystalline, possessing both α and β phases. Magnetic measurements determined that all of the nanoparticles were paramagnetic and did not exhibit a blocking temperature from 2 to 300 K. The multifunctional properties of these nanoparticles make them suitable for many applications, such as multimodal imaging probes, up-conversion fluorescent markers, as well as MRI contrast agents.

Observation of unusual slow-relaxation of the magnetisation in a Gd-EDTA chelate.

A Gadolinium EDTA chelate displays characteristic isotropic behaviour common of Gd(III) complexes under zero applied magnetic field, and anisotropic behaviour arising from dipolar coupling and weak spin-phonon coupling under an applied magnetic field. This surprising magnetic behaviour for Gd(III) is investigated using SQUID magnetometry and rationalized through theoretical calculations.

Slight synthetic changes eliciting different topologies: synthesis, structure and magnetic properties of novel dinuclear and nonanuclear dysprosium complexes

Using the Schiff-base ligand 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide (H2hmc), dinuclear and nonanuclear compounds, [Dy2(Hhmc)2(NO3)4]·THF·MeCN (1) and [Dy9(μ3-O)4(μ-OH)6(hmc)4(NO3)4(DMF)4](OH)·H2O·THF·DMF (2) are generated through the addition of different bases, respectively. Single-crystal X-ray diffraction analysis revealed a unique Dy9 core structure of complex 2, and the magnetic properties of both compounds are fully studied.

Intercalation of Coordinatively Unsaturated FeIII Ion within Interpenetrated Metal–Organic Framework MOF-5

Coordinatively unsaturated Fe(III) metal sites were successfully incorporated into the iconic MOF-5 framework. This new structure, Fe(III) -iMOF-5, is the first example of an interpenetrated MOF linked through intercalated metal ions. Structural characterization was performed with single-crystal and powder XRD, followed by extensive analysis by spectroscopic methods and solid-state NMR, which reveals the paramagnetic ion through its interaction with the framework. EPR and Mössbauer spectroscopy confirmed that the intercalated ions were indeed Fe(III) , whereas DFT calculations were employed to ascertain the unique pentacoordinate architecture around the Fe(III) ion. Interestingly, this is also the first crystallographic evidence of pentacoordinate Zn(II) within the MOF-5 SBU. This new MOF structure displays the potential for metal-site addition as a framework connector, thus creating further opportunity for the innovative development of new MOF materials.

Probing the structural and magnetic properties of a new family of centrosymmetric dinuclear lanthanide complexes

A series of centrosymmetric dinuclear lanthanide complexes, including Gd​III (1), Dy​III (2), Ho​III (3), Er​III (4) and Yb​III (5), have been synthesized and studied for the effects of lanthanide contraction on their magnetic properties. As a result of probing the magnetic properties of the Gd​III analogue, 1, a weak antiferromagnetic intramolecular interaction was confirmed, with J = −0.01 cm−1 and g = 2.01. The DyIII complex, 2, was found to exhibit larger values of gx and gy in the ground doublet of individual DyIII ions via ab initio calculations, and thus did not act as a SMM. Interestingly, the ErIII (4) and YbIII (5) complexes exhibited slow relaxation of the magnetization under an applied dc field with effective energy barriers (Ueff) of 21 K and 22 K, respectively.

A propeller-shaped μ4-carbonate hexanuclear dysprosium complex with a high energetic barrier to magnetisation relaxation

A Dy6 complex composed of two Dy3 triangular units, [Dy6(μ3-OH)(CO3)3(bsc)3(MeOH)14(H2O)](Cl)5·(H2O)·(MeOH)2 (1), was isolated and found to exhibit slow relaxation of the magnetisation under zero applied dc field, resulting in a high energetic barrier to relaxation.

Enchaining EDTA-chelated lanthanide molecular magnets into ordered 1D networks

Extending molecular systems into chain networks is a unique method with which to orient magnetic molecules into well-ordered arrays along one dimension, and study their resulting properties. Complexes of the formula Na[Ln(EDTA)(H2O)3]n·5H2O are presented, where Ln = YIII (1), EuIII (2), TbIII (3), DyIII (4). EDTA chain-like architectures were obtained in water by adding Na+ as a bridging ion. Structures were characterized using single crystal X-ray diffraction, and X-ray powder diffraction. Infrared spectroscopy and elemental analysis were performed on all samples in order to confirm bulk purity of the products. Direct current and alternating current magnetic susceptibility measurements were carried out on all paramagnetic complexes in order to investigate any potential magnetic interactions between ions, as well as potential dynamic magnetic properties. TbIII (3) and DyIII (4) compounds were confirmed to exhibit slow relaxation of the magnetization under an optimized applied dc field. Energy barriers to magnetic relaxation and pre-exponential factors differed dramatically between the lanthanide analogues, thus, magnetostructural correlations were performed using shape analysis techniques, which explained the presence of multiple relaxation processes. Furthermore, the trajectory of the anisotropy axes of the DyIII ions in 4 was modelled and compared with our previously studied GdIII system.