Confining single Er3+ ions in sub-3 nm NaYF4 nanoparticles to induce slow relaxation of the magnetisation.

Molecular systems known as single-molecule magnets (SMMs) exhibit magnet-like behaviour of slow relaxation of the magnetisation and magnetic hysteresis and have potential application in high-density memory storage or quantum computing. Often, their intrinsic magnetic properties are plagued by low-energy molecular vibrations that lead to phonon-induced relaxation processes, however, there is no straightforward synthetic approach for molecular systems that would lead to a small amount of low-energy vibrations and low phonon density of states at the spin-resonance energies. In this work, we apply knowledge accumulated over the last decade in molecular magnetism to nanoparticles, incorporating Er3+ ions in an ultrasmall sub-3 nm diamagnetic NaYF4 nanoparticle (NP) and probing the slow relaxation dynamics intrinsic to the Er3+ ion. Furthermore, by increasing the doping concentration, we also investigate the role of intraparticle interactions within the NP. The knowledge gained from this study is anticipated to enable better design of magnetically high-performance molecular and bulk magnets for a wide variety of applications, such as molecular electronics.

Synthesis, characterisation and reactivity of a zinc triazenide for potential use in vapour deposition.

In this study, we synthesised and characterised a new zinc(II) triazenide for potential use in vapour deposition of zinc sulphide thin films. The compound is volatile and quantitatively sublimes at 80 °C under vacuum (0.5 mbar). Thermogravimetric analysis showed a one-step volatilisation with an onset temperature at ∼125 °C and 5% residual mass. The compound also reacted with 2 or 4 molar equivalents of triphenylsilanethiol to give dimeric and monomeric zinc thiolates, respectively. The high volatility, thermal stability, and reactivity with sterically hindered thiols makes this compound a potential candidate for use in vapour deposition of zinc containing thin films.

Alkyl-Substituted Aminobis(phosphonates)-Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions.

The efficient and environmentally sustainable separation process for rare earth elements (REE), especially for adjacent lanthanoids, remains a challenge due to the chemical similarity of REEs. Tetravalent actinoids, thorium, and traces of uranium are also present in concentrates of REEs, making their separation relevant. This study reports six simple water-soluble aminobis(phosphonate) ligands, RN[CH2P(O)(OH)2]2 (1 R = CH2CH3, 2 R = (CH2)2CH3, 3 R = (CH2)3CH3, 4 R = (CH2)4CH3, 5 R = (CH2)5CH3, 6 R = CH2CH(C2H5)(CH2)3CH3) as precipitating agents for REEs, Th, and U, as well as gives insight into the coordination modes of the utilized ligands with REEs at the molecular level. Aminobis(phosphonates) 4-6 with longer carbon chains were found to separate selectively thorium, uranium, and scandium from REEs with short precipitation time (15 min) and excellent separation factors that generally range from 100 to 2000 in acidic aqueous solution. Ligands 1-6 also improved separation factors for adjacent lanthanoids in comparison to traditional oxalate precipitation agents. Importantly, precipitated metals can be recovered from the ligands with 3 molar HNO3 with no observed ligand decomposition enabling the possibility of recycling the ligands in the separation process. NMR-monitored pH titrations for 1 showed deprotonation steps at pK a 1.3, 5.55, and >10.5, which indicate that the ligands remain in a deprotonated [L]-1 form in the pH range of 0-4 used in the precipitation studies. 31P NMR titration studies between 1 and M(NO3)3 (M = Y, La, Lu) gave satisfactory fits for 1:3, 1:2, and 1:1 metal-ligand stoichiometries for Y, La, and Lu, respectively, according to an F-test. Therefore, aminobis(phosphonate) precipitation agents 1-6 are likely to form metal complexes with fewer ligands than traditional separation agents like DEHPA, which coordinates to REEs in 1:6 metal-ligand ratio.

Probing optical and magnetic properties via subtle stereoelectronic effects in mononuclear DyIII-complexes.

Tapping into the secondary coordination environment of mononuclear DyIII-complexes leads to drastic changes in luminescence and magnetism. Visualization of effects induced by stereoelectronics on the opto-magnetic properties was achieved through subtle modifications in the ligand framework.

Asymmetric Ring Opening in a Tetrazine-Based Ligand Affords a Tetranuclear Opto-Magnetic Ytterbium Complex.

We report the formation of a tetranuclear lanthanide cluster, [Yb4 (bpzch)2 (fod)10 ] (1), which occurs from a serendipitous ring opening of the functionalised tetrazine bridging ligand, bpztz (3,6-dipyrazin-2-yl-1,2,4,5-tetrazine) upon reacting with Yb(fod)3 (fod- =6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octandionate). Compound 1 was structurally elucidated via single-crystal X-ray crystallography and subsequently magnetically and spectroscopically characterised to analyse its magnetisation dynamics and its luminescence behaviour. Computational studies validate the observed MJ energy levels attained by spectroscopy and provides a clearer picture of the slow relaxation of the magnetisation dynamics and relaxation pathways. These studies demonstrate that 1 acts as a single-molecule magnet (SMM) under an applied magnetic field in which the relaxation occurs via a combination of Raman, direct, and quantum tunnelling processes, a behaviour further rationalised analysing the luminescent properties. This marks the first lanthanide-containing molecule that forms by means of an asymmetric tetrazine decomposition.

Anion-driven encapsulation of cationic guests inside pyridine[4]arene dimers.

Pyridine[4]arenes have previously been considered as anion binding hosts due to the electron-poor nature of the pyridine ring. Herein, we demonstrate the encapsulation of Me4N+ cations inside a dimeric hydrogen-bonded pyridine[4]arene capsule, which contradicts with earlier assumptions. The complexation of a cationic guest inside the pyridine[4]arene dimer has been detected and studied by multiple gas-phase techniques, ESI-QTOF-MS, IRMPD, and DT-IMMS experiments, as well as DFT calculations. The comparison of classical resorcinarenes with pyridinearenes by MS and NMR experiments reveals clear differences in their host-guest chemistry and implies that cation encapsulation in pyridine[4]arene is an anion-driven process.

Triplet-State Position and Crystal-Field Tuning in Opto-Magnetic Lanthanide Complexes: Two Sides of the Same Coin.

Lanthanide-complex-based luminescence thermometry and single-molecule magnetism are two effervescent fields of research, owing to the great promise they hold from an application standpoint. The high thermal sensitivity achievable, their contactless nature, along with sub-micrometric spatial resolution make these luminescent thermometers appealing for accurate temperature probing in miniaturised electronics. To that end, single-molecule magnets (SMMs) are expected to revolutionise the field of spintronics, thanks to the improvements made in terms of their working temperature-now surpassing that of liquid nitrogen-and manipulation of their spin state. Hence, the combination of such opto-magnetic properties in a single molecule is desirable in the aim of overcoming, among others, addressability issues. Yet, improvements must be made through design strategies for the realisation of the aforementioned goal. Moving forward from these considerations, we present a thorough investigation of the effect that changes in the ligand scaffold of a family of terbium complexes have on their performance as luminescent thermometers and SMMs. In particular, an increased number of electron-withdrawing groups yields modifications of the metal coordination environment and a lowering of the triplet state of the ligands. These effects are tightly intertwined, thus, resulting in concomitant variations of the SMM and the luminescence thermometry behaviour of the complexes. Supported by ab initio calculations, we can rationally interpret the observed trends and provide solid foundations for the development of opto-magnetic lanthanide complexes.

A Luminescent Thermometer Exhibiting Slow Relaxation of the Magnetization: Toward Self-Monitored Building Blocks for Next-Generation Optomagnetic Devices.

The development and integration of Single-Molecule Magnets (SMMs) into molecular electronic devices continue to be an exciting challenge. In such potential devices, heat generation due to the electric current is a critical issue that has to be considered upon device fabrication. To read out accurately the temperature at the submicrometer spatial range, new multifunctional SMMs need to be developed. Herein, we present the first self-calibrated molecular thermometer with SMM properties, which provides an elegant avenue to address these issues. The employment of 2,2'-bipyrimidine and 1,1,1-trifluoroacetylacetonate ligands results in a dinuclear compound, [Dy2(bpm)(tfaa)6], which exhibits slow relaxation of the magnetization along with remarkable photoluminescent properties. This combination allows the gaining of fundamental insight in the electronic properties of the compound and investigation of optomagnetic cross-effects (Zeeman effect). Importantly, spectral variations stemming from two distinct thermal-dependent mechanisms taking place at the molecular level are used to perform luminescence thermometry over the 5-398 K temperature range. Overall, these properties make the proposed system a unique molecular luminescent thermometer bearing SMM properties, which preserves its temperature self-monitoring capability even under applied magnetic fields.

Thermodynamically driven self-assembly of pyridinearene to hexameric capsules.

Pyridinearene macrocycles have previously shown unique host-guest properties in their capsular dimers including endo complexation of neutral molecules and exo complexation of anions. Here, we demonstrate for the first time the formation of hydrogen bonded hexamer of tetraisobutyl-octahydroxypyridinearene in all three states of matter - gas phase, solution and solid-state. Cationic tris(bipyridine)ruthenium(ii) template was found to stabilize the hexamer in gas phase, whereas solvent molecules do this in condensed phases. In solution, the capsular hexamer was found to be the thermodynamically favoured self-assembly product and transition from dimer to hexamer occurred in course of time. The crystal structure of hexamer revealed 24 N-HO direct intermolecular hydrogen bonds between the six pyridinearene macrocycles without any bridging solvent molecules. Hydrogen bond patterns correlate well with DFT computed structures. Thus, all structural chemistry methods (IM-MS, DOSY NMR, DFT, X-ray crystallography) support the same structure of the hexameric capsule that has a diameter of ca. 3 nm and volume of 1160 Å3.

Synthesis, Stability and Relaxivity of TEEPO-Met: An Organic Radical as a Potential Tumour Targeting Contrast Agent for Magnetic Resonance Imaging.

Cancer is a widespread and life-threatening disease and its early-stage diagnosis is vital. One of the most effective, non-invasive tools in medical diagnostics is magnetic resonance imaging (MRI) with the aid of contrast agents. Contrast agents that are currently in clinical use contain metals, causing some restrictions in their use. Also, these contrast agents are mainly non-specific without any tissue targeting capabilities. Subsequently, the interest has notably increased in the research of organic, metal-free contrast agents. This study presents a new, stable organic radical, TEEPO-Met, where a radical moiety 2,2,6,6-tetraethylpiperidinoxide (TEEPO) is attached to an amino acid, methionine (Met), as a potentially tumour-targeting moiety. We describe the synthesis, stability assessment with electron paramagnetic resonance (EPR) spectroscopy and relaxation enhancement abilities by an in vitro nuclear magnetic resonance (NMR) and phantom MRI studies of TEEPO-Met. The new compound proved to be stable notably longer than the average imaging time in conditions mimicking a biological matrix. Also, it significantly reduced the relaxation times of water, making it a promising candidate as a novel tumour targeting contrast agent for MRI.

Thermal expansion and magnetic properties of benzoquinone-bridged dinuclear rare-earth complexes.

The synthesis and structural characterization of two benzoquinone-bridged dinuclear rare-earth complexes [BQ(MCl2·THF3)2] (BQ = 2,5-bisoxide-1,4-benzoquinone; M = Y (1), Dy (2)) are described. Of these reported metal complexes, the dysprosium analogue 2 is the first discrete bridged dinuclear lanthanide complex in which both metal centres reside in pentagonal bipyramidal environments. Interestingly, both complexes undergo significant thermal expansion upon heating from 120 K to 293 K as illustrated by single-crystal X-ray and powder diffraction experiments. AC magnetic susceptibility measurements reveal that 2 does not show the slow relation of magnetization in zero dc field. The absent of single-molecule behaviour in 2 arises from the rotation of the principal magnetic axis as compared to the pseudo-C5 axis of the pentagonal bipyramidal environment as suggested by ab initio calculations. The cyclic voltammetry and chemical reduction experiments demonstrated that complexes 1 and 2 can be reduced to radical species containing [BQ3˙-]. This study establishes efficient synthetic strategy to make bridged redox-active multinuclear lanthanide complexes with a pentagonal bipyramidal coordination environment that are potential precursors for single-molecule magnets.

Simultaneous endo and exo†Complex Formation of Pyridine[4]arene Dimers with Neutral and Anionic Guests.

The formation of complexes between hexafluorophosphate (PF6- ) and tetraisobutyloctahydroxypyridine[4]arene has been thoroughly studied in the gas phase (ESI-QTOF-MS, IM-MS, DFT calculations), in the solid state (X-ray crystallography), and in chloroform solution (1 H, 19 F, and DOSY NMR spectroscopy). In all states of matter, simultaneous endo complexation of solvent molecules and exo complexation of a PF6- anion within a pyridine[4]arene dimer was observed. While similar ternary complexes are often observed in the solid state, this is a unique example of such behavior in the gas phase.

Strong Exchange Coupling in a Trimetallic Radical-Bridged Cobalt(II)-Hexaazatrinaphthylene Complex.

Reducing hexaazatrinaphthylene (HAN) with potassium in the presence of 18-c-6 produces [{K(18-c-6)}HAN], which contains the S=1/2 radical [HAN](.-) . The [HAN](.-) radical can be transferred to the cobalt(II) amide [Co{N(SiMe3 )2 }2 ], forming [K(18-c-6)][(HAN){Co(N'')2 }3 ]; magnetic measurements on this compound reveal an S=4 spin system with strong cobalt-ligand antiferromagnetic exchange and J≈-290 cm(-1) (-2 J formalism). In contrast, the Co(II) centres in the unreduced analogue [(HAN){Co(N'')2 }3 ] are weakly coupled (J≈-4.4 cm(-1) ). The finding that [HAN](.-) can be synthesized as a stable salt and transferred to cobalt introduces potential new routes to magnetic materials based on strongly coupled, triangular HAN building blocks.

Open-shell doublet character in a hexaazatrinaphthylene trianion complex.

Three-electron reduction of hexaazatrinaphthylene (HAN) with a magnesium(I) reagent leads to [(HAN){Mg(nacnac)}3] (1), containing a [HAN](3-) ligand with a spin of S = 1/2. Ab initio calculations reveal that the [HAN](3-) ligand in 1 has a ground-state wave function with multiconfigurational properties, and can be described as a triradicaloid species with a small amount of open-shell doublet character.