Spin-State Control in Dysprosium(III) Metallacrown Magnets via Thioacetal Modification.

Integrating controllable spin states into single-molecule magnets (SMMs) enables precise manipulation of magnetic interactions at a molecular level, but remains a synthetic challenge. Herein, we developed a 3d-4f metallacrown (MC) magnet [DyNi5(quinha)5(Clsal)2(py)8](ClO4) ⋅ 4H2O (H2quinha=quinaldichydroxamic acid, HClsal=5-chlorosalicylaldehyde) wherein a square planar NiII is stabilized by chemical stacking. Thioacetal modification was employed via post-synthetic ligand substitutions and yielded [DyNi5(quinha)5(Clsaldt)2(py)8](ClO4) ⋅ 3H2O (HClsaldt=4-chloro-2-(1,3-dithiolan-2-yl)phenol). Thanks to the additional ligations of thioacetal onto the NiII site, coordination-induced spin state switching (CISSS) took place with spin state altering from low-spin S=0 to high-spin S=1. The synergy of CISSS effect and magnetic interactions results in distinct energy splitting and magnetic dynamics. Magnetic studies indicate prominent enhancement of reversal barrier from 57 cm-1 to 423 cm-1, along with hysteresis opening and an over 200-fold increment in coercive field at 2 K. Ab initio calculations provide deeper insights into the exchange models and rationalize the relaxation/tunnelling pathways. These results demonstrate here provide a fire-new perspective in modulating the magnetization relaxation via the incorporation of controllable spin states and magnetic interactions facilitated by the CISSS approach.

Phase Transition Control in Molecular Solids via Complementarity of Hydrogen-Bond Strength.

Phase transitions in molecular solids involve synergistic changes in chemical and electronic structures, leading to diversification in physical and chemical properties. Despite the pivotal role of hydrogen bonds (H-bonds) in many phase-transition materials, it is rare and challenging to chemically regulate the dynamics and to elucidate the structure-property relationship. Here, four high-spin CoII com-pounds were isolated and systematically investigated by modifying the ligand terminal groups (X = S, Se) and substituents (Y = Cl, Br). S-Cl and Se-Br undergo a reversible structural phase transition near room temperature, triggering the rotation of 15-crown-5 guests and the swing between syn- and anti-conformation of NCX- ligands, accompanied by switchable magnetism. Conversely, S-Br and Se-Cl retain stability in ordered and disordered phases, respectively. H-bonds geometric analysis and ab initio calculations reveal that the electronegativity of X and Y affects the strength of NY-ap-H···X interactions. Entropy-driven structural phase transitions occur when the H-bond strength is appropriate; otherwise, the phase stays unchanged if it is too strong or weak. This work highlights a phase transition driven by H-bond strength complementarity - pairing strong acceptor with weak donor and vice versa, which offers a straightforward and effective approach for designing phase-transition molecular solids from a chemical perspective.

High-stability spherical lanthanide nanoclusters for magnetic resonance imaging.

High-nuclear lanthanide clusters have shown great potential for the administration of high-dose mononuclear gadolinium chelates in magnetic resonance imaging (MRI). The development of high-nuclear lanthanide clusters with excellent solubility and high stability in water or solution has been challenging and is very important for expanding the performance of MRI. We used N-methylbenzimidazole-2-methanol (HL) and LnCl3·6H2O to synthesize two spherical lanthanide clusters, Ln32 (Ln = Ho, Ho32; and Ln = Gd, Gd32), which are highly stable in solution. The 24 ligands L- are all distributed on the periphery of Ln32 and tightly wrap the cluster core, ensuring that the cluster is stable. Notably, Ho32 can remain highly stable when bombarded with different ion source energies in HRESI-MS or immersed in an aqueous solution of different pH values for 24 h. The possible formation mechanism of Ho32 was proposed to be Ho(III), (L)- and H2O → Ho3(L)3/Ho3(L)4 → Ho4(L)4/Ho4(L)5 → Ho6(L)6/Ho6(L)7 → Ho16(L)19 → Ho28(L)15 → Ho32(L)24/Ho32(L)21/Ho32(L)23. To the best of our knowledge, this is the first study of the assembly mechanism of spherical high-nuclear lanthanide clusters. Spherical cluster Gd32, a form of highly aggregated Gd(III), exhibits a high longitudinal relaxation rate (1 T, r1 = 265.87 mM-1·s-1). More notably, compared with the clinically used commercial material Gd-DTPA, Gd32 has a clearer and higher-contrast T1-weighted MRI effect in mice bearing 4T1 tumors. This is the first time that high-nuclear lanthanide clusters with high water stability have been utilized for MRI. High-nuclear Gd clusters containing highly aggregated Gd(III) at the molecular level have higher imaging contrast than traditional Gd chelates; thus, using large doses of traditional gadolinium contrast agents can be avoided.

Reversible Switchability of Magnetic Anisotropy and Magnetodielectric Effect Induced by Intermolecular Motion.

Introducing magnetic switchability into artificial molecular machines is fascinating for precise control of magnetism via external stimuli. Herein, a field-induced CoII single-molecule magnet was found to exhibit the reversible switch of Jahn-Teller distortion near room temperature, along with thermal conformational motion of the 18-crown-6 rotor, which pulls the coordinated H2 O to rotate through intermolecular hydrogen bonds and triggers a single-crystal-to-single-crystal phase transition with Twarm =282 K and Tcool =276 K. Interestingly, the molecular magnetic anisotropy probed by single-crystal angular-resolved magnetometry revealed the reorientation of easy axis by 14.6°. Moreover, ON/OFF negative magnetodielectric effects were respectively observed in the high-/low-temperature phase, which manifests the spin-lattice interaction in the high-temperature phase could be stronger, in accompanied by the hydrogen bonding between the rotating 18-crown-6 and the coordinated H2 O.

Opening magnetic hysteresis via improving the planarity of equatorial coordination by hydrogen bonding.

Through a mixed-ligand strategy, the structural change from a discrete dinuclear DyIII cluster to a one-dimensional polymeric chain was achieved, maintaining the two magnetic entities with the same {Dy(dppbO2)2(H2O)5} (dppbO2 = 1,4-butylenebis(diphenylphosphine oxide)) core structure. Since the hydrogen bonding between the equatorial coordinated water molecules and the guests/solvents/anions is distinct, the local geometry and the equatorial planarity of the first coordination sphere of the central DyIII ion become slightly different caused by the second coordination sphere. As a result, the dinuclear compound shows typical butterfly-shaped hysteresis loops, while it significantly opens at zero magnetic field up to 11 K for the 1D polymer, which is unprecedented in coordination polymers. Our experimental observations and theoretical analysis indicate that the hydrogen bonding leads to the fine-tuning of certain bond lengths and angles of the coordination environment, as well as the crystal field to a certain extent, revealing that the second coordination sphere affects the first coordination sphere by hydrogen bonding.

Stereoisomeric coordination polymers based on facial and meridional six-coordinate dysprosium(III ).

Due to the small differences in the chemical properties of facial (fac) and meridional (mer) stereoisomers, selective synthesis of one of the isomers is challenging, especially for lanthanide complexes. By using a flexible bidentate phosphine oxide ligand, we managed to isolate three stereoisomeric 2D and 3D coordination polymers, in which six-coordinate Dy(III) ions possess fac- or mer-Cl3O3 coordination environments. Structural studies indicate that the stereochemistry differences result from their various supramolecular interactions (e.g., hydrogen bonding and π⋯π stacking). Magnetic property measurements reveal the different static and dynamic magnetic behaviours of the three stereoisomers. Ab initio CASSCF calculations were then performed which indicated that their distinct magnetic behaviours arise from their fac/mer configurations. Compared to fac-Dy(III), mer-Dy(III) possesses more axial ground-state KDs and higher first excited KDs.

The effectiveness and safety of linagliptin within elderly type 2 diabetes mellitus: a meta-analysis and systematic review.

BACKGROUND: Linagliptin is a convenient and effective drug approved for glycemic management in type 2 diabetes mellitus (T2DM). However, the effectiveness and safety evidence of linagliptin remains unclear with the increasing prevalence of T2DM in elderly patients. OBJECTIVE: For evaluating the effectiveness and safety of linagliptin within T2DM cases who aged ≥60 years. METHODS: The researchers pooled 4903 cases aged ≥60 years with T2DM from 5 published randomized clinical trials obtained from multiple databases. The safety was evaluated by the incidence and severity of adverse events (AEs) which mainly focused on hypoglycaemia. The major effectiveness end point was the change of glycated haemoglobin (HbA1c). Then the researchers made the qualitative and quantitative assessments of the investigation. RESULTS: The level of HbA1c and FPG was significantly reduced by linagliptin (WMD=-0.63%, 95% CI: -0.81, -0.44; p<0.00001; Z=6.70) and (WMD=-15.58 mg/dL, 95% CI: -22.34, -8.82; p<0.00001; Z=4.52) relative to that in the placebo cohort. The incidences of overall (OR=1.01, 95% CI: 0.82, 1.25; p=0.91) and severe negative events (OR=0.88, 95% CI: 0.61, 1.25; p=0.46) were not significant increased in linagliptin cohorts compared to the placebo cohorts. There is insignificant difference in hypoglycaemia between linagliptin and placebo cohorts for the 24 weeks' study(OR=1.12, 95% CI: 0.85, 1.48; p=0.41). Severe hypoglycemia had slightly descended incidence, whereas insignificant difference was shown in the linagliptin cohorts in contrast to placebo cohorts (OR=0.95, 95 % CI: 0.68, 1.32, p=0.76). CONCLUSIONS: Linagliptin is an effective drug with excellent safety for elderly T2DM.

Medial patellofemoral ligament reconstruction: A review.

INTRODUCTION: Reconstruction of the medial patellofemoral ligament (MPFL) is an effective surgical method for the treatment of lateral patellar instability. At present, there is not much controversies regarding the femoral attachment, however, the controversies regarding patellar attachment versus attachment, number of graft strands, tension, isometry and so on. The following electronic databases will be searched: PubMed, the Cochrane Library, Embase, Web of Science, Medline. We will consider articles published between database initiation and March 2021. MPFL in the subject heading will be included in the study. Language is limited to English. Research selection, data extraction, and research quality assessment were independently completed by 2 researchers. CONCLUSIONS: MPFL reconstruction is a reliable technique for the treatment of patellofemoral instability. The Schöttle point is still the mainstream method for locating the femoral attachment, the patellar attachment for single-bundle is located at the junction of the proximal one third and the distal two third of the longitudinal axis of the patella. For double-bundles, one is located in the proximal one third of the medial patellar edge and another is in the center of the patellar edge. Meanwhile, the adjustment of graft tension during operation is very important.

Self-Assembly Synthesis of a [2]Catenane CoII Single-Molecule Magnet.

We describe herein the self-assembly synthesis of an octanuclear CoII [2]catenane {[Co4 (H2 L)6 ]2 16+ } formed by the mechanical interlocking of two {[Co4 (H2 L)6 ]8+ } rectangles of unprecedented topology. Subtle manipulation of the synthetic conditions allows the isolation of a mixed-valence [Co2 III /Co2 II ]10+ non-catenated rectangle. The CoII centers in the [2]catenane exhibit slow relaxation of their magnetic moment, i. e. single-molecule magnet properties, dominated by quantum tunneling and Raman relaxation processes. This work shows that metallo-supramolecular chemistry can precisely control the organization of single-molecule magnets in topologically complex arrangements.

Fascinating interlocked triacontanuclear giant nanocages.

We report herein three air, thermal and solvent stable interlocked triacontanuclear giant nanocages, generated using a node and spacer concept. Interestingly, the crystal structures of the cages are not only nano-dimensional but also exist in the nano-dimension range, which was corroborated with microscopic images. The combination of microscopic and crystallographic data, in effect, led us to a unique advantageous situation of generating nanomaterials with hard-to-come-by structural information at the molecular level.

Magnetization Dynamics on Isotope-Isomorphic Holmium Single-Molecule Magnets.

Here we reported the deuteration of the metal-binding equatorial water molecules in a reported HoIII single-molecule magnet (SMM) with pentagonal-bipyramidal geometry, from [Ho(CyPh2 PO)2 (H2 O)5 ]3+ to [Ho(CyPh2 PO)2 (D2 O)5 ]3+ . The hyperfine structures originating from the nuclear spin of 165 HoIII can be clearly observed. Moreover, the resulting magnetization dynamics revealed the switch of the relative relaxation rates for the two isotope-isomorphic complexes-respectively faster/slower at low/high temperature. The noticeable isotope effect arises from not only the paramagnetic metal center but also the diamagnetic ligands, which can be explained by the ab initio calculated tunnel splitting and the involvement of the super-hyperfine interaction related to the difference in the nuclear spin number of protium (1 H, I=1 /2 ) and deuterium (2 H, I=1).

Tuning luminescence of didysprosium single-molecule magnets with a π-conjugated/non-conjugated bridging ligand.

Herein, we reported two didysprosium single-molecule magnets constructed with {Dy(bbpen)(MeOH)} subunits and a π-conjugated tpb or non-conjugated tpcb bridging ligand. The former exhibits extremely weak luminescence that makes it difficult to simulate its emission spectra. However, the later shows obviously enhanced and well-resolved luminescence, which helps us to gain knowledge about the magneto-optical correlation and the relevant magnetic energy levels.

Opening Magnetic Hysteresis by Axial Ferromagnetic Coupling: From Mono-Decker to Double-Decker Metallacrown.

Combining Ising-type magnetic anisotropy with collinear magnetic interactions in single-molecule magnets (SMMs) is a significant synthetic challenge. Herein we report a Dy[15-MCCu -5] (1-Dy) SMM, where a DyIII ion is held in a central pseudo-D5h pocket of a rigid and planar Cu5 metallacrown (MC). Linking two Dy[15-MCCu -5] units with a single hydroxide bridge yields the double-decker {Dy[15-MCCu -5]}2 (2-Dy) SMM where the anisotropy axes of the two DyIII ions are nearly collinear, resulting in magnetic relaxation times for 2-Dy that are approximately 200 000 times slower at 2 K than for 1-Dy in zero external field. Whereas 1-Dy and the YIII -diluted Dy@2-Y analogue do not show remanence in magnetic hysteresis experiments, the hysteresis data for 2-Dy remain open up to 6 K without a sudden drop at zero field. In conjunction with theoretical calculations, these results demonstrate that the axial ferromagnetic Dy-Dy coupling suppresses fast quantum tunneling of magnetization (QTM). The relaxation profiles of both complexes curiously exhibit three distinct exponential regimes, and hold the largest effective energy barriers for any reported d-f SMMs up to 625 cm-1 .

Magnetic dynamics of an open-ring tridysprosium complex employing mixed ligands.

By employing mixed ligands, a new trinuclear dysprosium complex [Dy3(dbm)3(L)4](ClO4)2·CH2Cl2·2MeOH (1, Hdbm = dibenzoylmethane; HL = 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol) was synthesized by a one-pot reaction. According to structural characterization, all the 8-coordinated Dy(iii) sites are well arranged with slightly distorted square antiprism (D4d) geometries. Magnetic measurements reveal that 1 exhibits typical single-molecule magnetic behavior at zero magnetic field and shows rarely open hysteresis loops up to 3 K among open-ring {Dy3} SMMs, where the relaxation time remains very stable under the protection from the Dy-Dy magnetic coupling in the open-ring arrangement of Ising spins.

Coercive Fields Above 6†T in Two Cobalt(II)-Radical Chain Compounds.

Lanthanide permanent magnets are widely used in applications ranging from nanotechnology to industrial engineering. However, limited access to the rare earths and rising costs associated with their extraction are spurring interest in the development of lanthanide-free hard magnets. Zero- and one-dimensional magnetic materials are intriguing alternatives due to their low densities, structural and chemical versatility, and the typically mild, bottom-up nature of their synthesis. Here, we present two one-dimensional cobalt(II) systems Co(hfac)2 (R-NapNIT) (R-NapNIT=2-(2'-(R-)naphthyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, R=MeO or EtO) supported by air-stable nitronyl nitroxide radicals. These compounds are single-chain magnets and exhibit wide, square magnetic hysteresis below 14 K, with giant coercive fields up to 65 or 102 kOe measured using static or pulsed high magnetic fields, respectively. Magnetic, spectroscopic, and computational studies suggest that the record coercivities derive not from three-dimensional ordering but from the interaction of adjacent chains that compose alternating magnetic sublattices generated by crystallographic symmetry.

Slow magnetic dynamics in centrosymmetric didysprosium and equilateral triangular tridysprosium molecules.

Single-molecule magnets (SMMs) with higher nuclearity provide opportunity for understanding the inherent nature of magnetic dynamics that are not limited to mononuclear SMMs. Herein, centrosymmetric [Dy2(L)2(9-AC)4(MeOH)2]·2CH2Cl2·2H2O (1, where 9-AC = anthracene-9-carboxylate) and equilateral triangular [Dy3(OH)(OMe)(L)3(dbm)3](OH)·3CH2Cl2·7H2O (2, where dbm = dibenzoylmethane anion) were isolated using the Schiff-base ligand 4-(anthracen-9-yl)-2-((quinolin-8-ylimino)methyl)phenol (HL). Static and dynamic magnetic measurements reveal that 1 and 2 display slow magnetic relaxation under zero and applied dc field, respectively. The magnetization relaxation for 1 is dominated by a Raman process due to its non-negligible transverse anisotropy. Complex 2 exhibits field-induced SMM behavior with a reversal barrier of 56 cm-1. By means of ab initio calculations and magnetic measurements, the multiple relaxation regime in 2 was investigated. We suggest that Orbach and Raman mechanisms dominate in the high/low temperature domains, respectively.

Access to Heteroleptic Fluorido-Cyanido Complexes with a Large Magnetic Anisotropy by Fluoride Abstraction.

Silicon-mediated fluoride abstraction is demonstrated as a means of generating the first fluorido-cyanido transition metal complexes. This new synthetic approach is exemplified by the synthesis and characterization of the heteroleptic complexes, trans-[MIV F4 (CN)2 ]2- (M=Re, Os), obtained from their homoleptic [MIV F6 ]2- parents. As shown by combined high-field electron paramagnetic resonance spectroscopy and magnetization measurements, the partial substitution of fluoride by cyanide ligands leads to a marked increase in the magnetic anisotropy of trans-[ReF4 (CN)2 ]2- as compared to [ReF6 ]2- , reflecting the severe departure from an ideal octahedral (Oh point group) ligand field. This methodology paves the way toward the realization of new heteroleptic transition metal complexes that may be used as highly anisotropic building-blocks for the design of high-performance molecule-based magnetic materials.

Cyanometallate-Bridged Didysprosium Single-Molecule Magnets Constructed with Single-Ion Magnet Building Block.

The combination of magnetic interaction with high magnetic anisotropy provides a promising way for modulating/fine-tuning molecular magnetic behaviors. Here, we show the building block approach for the synthesis of a family of dilanthanide single-molecule magnets (SMMs) bridged with a cyanometallate starting from a monolanthanide SMM. Contingent on the central para-/diamagnetic [M(CN)6]3- (M = Fe, Co) integrated between two highly anisotropic pentagonal-bipyramid Dy(III) subunits, the remanence of magnetization is OFF/ON below 15 K and they respectively display a record reversal barrier of 659 K among d-f SMMs and 975 K among cyano-bridged SMMs.

A square antiprism dysprosium single-ion magnet with an energy barrier over 900 K.

Herein we report a stable and high-performance Dy(iii) single-ion magnet (SIM) showing an energy barrier of 944 K under zero dc field, with an open hysteresis loop up to 6 K. To the best of our knowledge, this is the highest energy barrier for a square antiprism as well as phosphine oxide based Dy-SIMs, reported so far.