Dual magnetic field and temperature optical probes of controlled crystalline phases in lanthanide-doped multi-shell nanoparticles.

The engineering of core@multi-shell nanoparticles containing heterogeneous crystalline phases in different layers constitutes an important strategy for obtaining optical probes. The possibility of obtaining an opto-magnetic core@multi-shell nanoparticle capable of emitting in the visible and near-infrared ranges by upconversion and downshifting processes is highly desirable, especially when its optical responses are dependent on temperature and magnetic field variations. This work proposes the synthesis of hierarchically structured core@multi-shell nanoparticles of heterogeneous crystalline phases: a cubic core containing DyIII ions responsible for magnetic properties and optically active hexagonal shells, where ErIII, YbIII, and NdIII ions were distributed. This system shows at least three excitation energies located at different biological windows, and its emission intensities are sensitive to temperature and external magnetic field variations. The selected crystalline phases of the core@multi-shell nanoparticles obtained in this work is fundamental to the development of multifunctional materials with potential applications as temperature and magnetic field optical probes.

Anion-Dependent Catalytic C-C Bond Cleavage of a Lignin Model within a Cationic Metal-Organic Framework.

The development of heterogeneous catalysts capable of selectively converting lignin model compounds into products of added value offers an exciting avenue to explore in the production of renewable chemical feedstocks. The use of metal-organic frameworks (MOFs) in such chemical transformations relies largely on the presence of accessible open metal sites found within highly porous networks that simultaneously allow for fast transport and strong interactions with desired substrates. Here, we present the first systematic study on the modulation of catalytic performance of a cationic framework, [Cu2(L)(H2O)2](NO3)2·5.5H2O (L = 1,1'-bis(3,5-dicarboxylatophenyl)-4,4'-bipyridinium), achieved through the exchange of anionic guests. Remarkably, the catalytic activity proves to be highly anion-dependent, with a nearly 10-fold increase toward the aerobic C-C bond cleavage of a lignin model compound when different anionic species are incorporated within the MOF. Moreover, we demonstrate that the cationic nature of the MOF, imparted by the incorporation of viologen moieties within the linker, tunes the electrophilicity of the active copper(II) sites, resulting in stronger interactions with the substrate. As such, the copper-based framework exhibits enhanced catalytic performance when compared to its neutral counterpart, emphasizing the appeal of charged frameworks for use as green heterogeneous catalysts.

Shining New Light on Multifunctional Lanthanide Single-Molecule Magnets.

Single-molecule magnets (SMMs) are at the forefront of new technological advances in quantum information processing and spintronics. Despite the recent impressive breakthroughs in extending the magnetic blocking temperatures beyond liquid-nitrogen temperatures, significant challenges await in terms of integrating and addressing such compounds in devices. With this ultimate goal in mind, the design of multifunctional SMMs not only allows to imbue molecules of interest with specific properties that would allow for in situ monitoring of the SMM operation in real time, but can also provide critical insights into our understanding of the magnetic behaviour. In this Review, we highlight how magnetism and luminescence can be harmoniously combined within single molecules to achieve these objectives. The key design principles to attain the simultaneous combination of photoluminescence and slow relaxation of the magnetization are discussed, along with an outlook on how such molecules could be beneficial for emerging next-generation spintronics devices.

A Barrel-Shaped Metal-Organic Blue-Box Analogue with Photo-/Redox-Switchable Behavior.

Donor-acceptor interactions are ubiquitous in the design and understanding of host-guest complexes. Despite their non-covalent nature, they can readily dictate the self-assembly of complex architectures. Here, a photo-/redox-switchable metal-organic nanocapsule is presented, which was assembled by using lanthanide ions and viologen building blocks, by relying on such donor-acceptor interactions. The potential of this unique barrel-shaped structure is highlighted for the encapsulation of suitable electron donors, akin to the well-investigated "blue-box" macrocycles. The light-triggered reduction of the viologen units has been investigated by single-crystal-to-single-crystal X-ray diffraction experiments, complemented by magnetic, optical, and solid-state electrochemical characterizations. Density functional theory (DFT) calculations were employed to suggest the most likely electron donor in the light-triggered reduction of the viologen-based ligand.

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.

Exploring the dual functionality of an ytterbium complex for luminescence thermometry and slow magnetic relaxation.

We present a comprehensive investigation of the magnetic and optical properties of an ytterbium complex, which combines two desirable and practical features into a single molecular system. Based upon YbIII ions that promote near-infrared optical activity and a chemical backbone that is ideal for an in-depth understanding of the magnetic behaviour, we have designed a multifunctional opto-magnetic species that operates as a luminescent thermometer and as a single-molecule magnet (SMM). Our magnetic investigations, in conjunction with ab initio calculations, reveal one of the highest energy barriers reported for an YbIII-based complex. Moreover, we correlate this anisotropic barrier with the emission spectrum of the compound, wherein we provide a complete assignment of the energetic profile of the complex. Such studies lay the foundation for the design of exciting multi-faceted materials that are able to retain information at the single-molecule level and possess built-in thermal self-monitoring capabilities.

Design Strategy for the Controlled Generation of Cationic Frameworks and Ensuing Anion-Exchange Capabilities.

Cationic frameworks are an emerging class of exceptional solid adsorbents capable of encapsulating highly toxic and persistent anionic pollutants. The controlled generation of cationic frameworks, however, lags behind the abundant design strategies devised to control the structures and topologies of neutral frameworks. In this regard, we report a rational approach that allows the conversion of the synthetic approach toward constructing a neutral framework into one allowing for the synthesis of a cationic one without incurring any changes to the overall topology or the selected metal ion. We demonstrate that the replacement of a functional group on an organic linker that promotes a similar coordination mode, but bearing one less negative charge, can yield the systematic generation of cationic frameworks. Moreover, we confirm the cationic nature of the metal-organic frameworks through preliminary anion-exchange experiments and propose a method to retain permanent porosity in cationic frameworks through the use of strongly binding anions. Altogether, these results show great promise for the construction of tunable nanoporous frameworks capable of carrying out anion-exchange processes.

Ferromagnetically coupled dinuclear MII complexes based on a boratriazine ligand framework.

A boratriazine ligand, which incorporates attractive features from both bodipy and terpy, has been used to synthesize [Fe2II(µ1,1-N3)2(Py2F2BTA)2(N3)2] (1) and [Co2II(µ1,1-N3)2(Py2F2BTA)2(N3)2] (2). Both 1 and 2 feature a double end-on azido bridging motif, which promotes ferromagnetic interactions between the metal centres. Indeed, 1 represents the first report of a dinuclear FeII complex with this bridging mode exhibiting J = 5.7(9) cm-1 and D = -6.0(4) cm-1, while the isostructural Co analogue shows J = 7.1(9) cm-1 and D = 17.3(9) cm-1.

A nitrogen-rich ligand as a scaffold for slow magnetic relaxation in dysprosium-based 0D and 1D architectures.

A recently designed nitrogen-rich ligand is successfully applied as a scaffold for lanthanide ions to show that the intricate chemistry of energetic materials can be combined with other fields of research, including that of molecular magnetism. Herein, we report the synthesis of two different types of molecular architectures using a single ligand template, in which the discrete monomer exhibits single-molecule magnet-like behaviour along with two well-isolated modes of magnetic relaxation.

Strong ferromagnetic exchange coupling in a {Ni} cluster mediated through an air-stable tetrazine-based radical anion.

A planar tetradentate 3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine (BpymTz) templating chelate affords the formation of an unprecedented BpymTz˙- radical anion bridged {Ni} complex. Detailed magnetic measurements performed on the isolated air stable [Ni(BpymTz˙-)Cl6(DMF)8]Cl·0.5(H2O) compound reveal strong ferromagnetic NiII-BpymTz˙- interactions with a coupling constant of J = 98.84 cm-1.

Stepwise crystallographic visualization of dynamic guest binding in a nanoporous framework.

Binding sites are at the heart of all host-guest systems, whether biological or chemical. When considering binding sites that form covalent bonds with the guest, we generally envision a single, highly specific binding motif. Through single-crystal X-ray crystallography, the dynamic binding of a guest that displays a variety of covalent binding motifs in a single site of adsorption is directly observed for the first time. The stepwise crystallographic visualization of the incorporation of I2 within a porous MOF is presented, wherein the preferred binding motifs throughout the uptake process are identified. The guest I2 molecules initially bind with terminal iodide atoms of the framework to form [I4]2- units. However, as the adsorption progresses, the I2 molecules are observed to form less energetically favorable I3- groups with the same framework iodide atoms, thereby allowing for more guest molecules to be chemisorbed. At near saturation, even more binding motifs are observed in the same pores, including both physisorbed and chemisorbed guest molecules. Herein, we present the successful identification of a unique set of host-guest interactions which will drive the improvement of high capacity iodine capture materials.

Confinement effects of a crystalline sponge on ferrocene and ferrocene carboxaldehyde.

The pivotal role of ππ interactions in the inclusion behaviour of a series of organometallic sandwich compounds is studied through single-crystal X-ray diffraction. The confinement effects of a crystalline sponge host are investigated where, notably, we observe an enhanced rotation of the ligand ring once encapsulated by the nanoporous framework, as evidenced by SSNMR experiments.

Slow Magnetic Relaxation Observed in Dysprosium Compounds Containing Unsupported Near-Linear Hydroxo- and Fluoro-Bridges.

The encapsulating N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H2valdien) ligand was employed to isolate two novel Dy(III) compounds which contain rare bridging pathways for lanthanide systems. Compound 1, [Na2Dy(III)2(valdien)2(µ-OH)(dbm)2(H2O)2][Na2Dy(III)2(valdien)2(µ-OH)(NO3)2(dbm)2], where dbm(-) is dibenzoylmethanido, and compound 2, [Na3Dy(III)2(valdien)2(µ-F)(µ3-F)2(Cl)2(MeOH)2]n·0.5(MeOH)·(H2O), both exhibit linear lone hydroxo- and fluoro-bridges, respectively, between the metal centers. The unit cell of 1 comprises two discrete dinuclear molecules, which differ slightly, forming a cation-anion pair, while 2 forms a coordination polymer. The magnetic investigations indicate that both compounds display ferromagnetic coupling between the Dy(III) ions. Magnetic susceptibility measurements in the temperature range 1.8-300 K reveal that the Dy(III) ions in 1 are weakly coupled, resulting in a mononuclear single-molecule magnet-like behavior under an applied field. In the case of 2, the stronger coupling arising from the fluoride-bridge, leads to zero-field single-molecule magnet (SMM) behavior with a non-negligible anisotropy barrier (Ueff) of 42 K.

Significant enhancement of energy barriers in dinuclear dysprosium single-molecule magnets through electron-withdrawing effects.

The effect of electron-withdrawing ligands on the energy barriers of Single-Molecule Magnets (SMMs) is investigated. By introducing highly electron-withdrawing atoms on targeted ligands, the energy barrier was significantly enhanced. The structural and magnetic properties of five novel SMMs based on a dinuclear {Dy2} phenoxo-bridged motif are explored and compared with a previously studied {Dy2} SMM (1). All complexes share the formula [Dy2(valdien)2(L)2]·solvent, where H2valdien = N1,N3-bis(3-methoxysalicylidene) diethylenetriamine, the terminal ligand L = NO3(-) (1), CH3COO(-) (2), ClCH2COO(-) (3), Cl2CHCOO(-) (4), CH3COCHCOCH3(-) (5), CF3COCHCOCF3(-) (6), and solvent = 0.5 MeOH (4), 2 CH2Cl2 (5). Systematic increase of the barrier was observed for all complexes with the most drastic increase seen in 6 when the acac ligand of 5 was fluorinated resulting in a 7-fold enhancement of the anisotropic barrier. Ab initio calculations reveal more axial g tensors as well as higher energy first excited Kramers doublets in 4 and 6 leading to higher energy barriers for those complexes.

Turning on single-molecule magnet behavior in a linear {Mn3} compound.

The synthesis, structure, and magnetic properties are reported for a new manganese compound with a mixed-valent {Mn(3)} core arranged in a linear fashion. The previously reported complex 1, [Mn(IV)(3)(dpo)(6)]·2MeCN, where H(2)dpo is (E)-1-hydroxy-1,1-diphenylpropan-2-one oxime, served as a starting point for the isolation of a {Mn(3)} compound with an analogous core arrangement through the reaction of Mn(OAc)(2)·4H(2)O, H(3)oxol ((E)-2,5-dihydroxy-2,5-dimethylhexan-3-one oxime), and NaOH in MeOH and MeCN. By using these reaction conditions, compound 2, Na[Mn(IV)(2)Mn(III)(Hoxol)(6)](n)·MeOH·H(2)O, was successfully isolated revealing a central Mn(III) ion thereby introducing structural and magnetic anisotropy to the system. The structure of 2 reveals linear trinuclear Mn(IV)-Mn(III)-Mn(IV) units connected through Na(+) ions forming a linear one-dimensional coordination polymer. The Jahn-Teller axes of each trinuclear unit are aligned parallel within the same chain and form a 75° angle between the two symmetry related chains. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9-300 K reveal that only the reduced compound, 2, is a single-molecule magnet (SMM) largely due to the anisotropy introduced by the Jahn-Teller distortions on the Mn(III) ions, which effectively induce this magnet behavior. Weak antiferromagnetic interactions along the chains through the Na(+) cations lead to a modulation of the intrinsic properties of the Mn(IV)-Mn(III)-Mn(IV) SMMs.

A novel high-spin tridecanuclear Ni(II) cluster with an azido-bridged core exhibiting disk-like topology.

A high-spin tridecanuclear Ni(II) cluster, [Ni(II)(13)(N(3))(18)(dpo)(4)(Hdpo)(2)(H(2)hpo)(4)(H(2)O)(MeOH)] [Ni(II)(13)(N(3))(18)(dpo)(4)(Hdpo)(2)(H(2)hpo)(4)(H(2)O)(2)] (1) (Hdpo = 1-(dimethylamino)propan-2-one oxime and H(2)hpo = 1-(hydroxyamino)propan-2-one oxime) with a purely azido-bridged core, is reported with dominant ferromagnetic coupling between Ni(II) ions. The latter molecule exhibits a unique planar core topology with the largest N(3)(-):Ni(II) ratio reported to date.