Substituent Positioning Effects on the Magnetic Properties of Sandwich-Type Erbium(III) Complexes with Bis(trimethylsilyl)-Substituted Cyclooctatetraenyl Ligands.

Lanthanide complexes with judiciously designed ligands have been extensively studied for their potential applications as single-molecule magnets. With the influence of ligands on their magnetic properties generally established, recent research has unearthed certain effects inherent to site differentiation due to the different types and varying numbers of substituents on the same ligand platform. Using two new sandwich-type Er(III) complexes with cyclooctatetraenyl (COT) ligands featuring two differently positioned trimethylsilyl (TMS) substituents, namely, [Li(DME)Er(COT1,5-TMS2)2]n (Er1) and [Na(DME)3][Er(COT1,3-TMS2)2] (Er2) [COT1,3-TMS2 and COT1,5-TMS2 donate 1,3- and 1,5-bis(trimethylsilyl)-substituted cyclooctatetraenyl ligands, respectively; DME = 1,2-dimethoxyethane], and with reference to previously reported [Li(DME)3][Er(COT1,4-TMS2)2] (A) and [K(DME)2][Er(COT1,4-TMS2)2] (B), any possible substituent position effects have been explored for the first time. The rearrangement of the TMS substituents from the starting COT1,4-TMS2 to COT1,3-TMS2 and COT1,5-TMS2, by way of formal migration of the TMS group, was thermally induced in the case of Er1, while for the formation of Er2, the use of Na+ in the placement of its Li+ and K+ congeners is essential. Both Er1 and Er2 display single-molecule magnetic behaviors with energy barriers of 170(3) and 172(6) K, respectively. Magnetic hysteresis loops, butterfly-shaped for Er1 and wide open for Er2, were observed up to 12 K for Er1 and 13 K for Er2. Studies of magnetic dynamics reveal the different pathways for relaxation of magnetization below 10 K, mainly by the Raman process for Er1 and by quantum tunneling of magnetization for Er2, leading to the order of magnitude difference in magnetic relaxation times and sharply different magnetic hysteresis loops.

Two Pairs of Homochiral Parallelogram-like Dy4 Cluster Complexes with Strong Magneto-Optical Properties.

Two pairs of homochiral Dy(III) tetranuclear cluster complexes derived from (+)/(-)-3-trifluoroacetyl camphor (D-Htfc/L-Htfc), [Dy4(OH)2(L1)4(D-tfc)2(DMF)2]·4DMF (D-1) [H2L1 = (E)-2-(2-hydroxy-3-methoxybenzylideneamino)phenol)]/[Dy4(OH)2(L1)4(L-tfc)2(DMF)2]·4DMF (L-1) and [Dy4(OH)2(L2)4(D-tfc)2(DMF)2]·2H2O·3MeCN (D-2) [H2L2 = (E)-3-(2-hydroxy-3-methoxybenzylideneamino)naphthalen-2-ol]/[Dy4(OH)2(L2)4(L-tfc)2(DMF)2]·2H2O·3MeCN (L-2), were synthesized at room temperature, which have a Dy4 parallelogram-like core. The magnetic studies revealed that D-1 exhibits single-molecule magnet (SMM) behavior under zero dc magnetic field, and its magnetic relaxation has a distinct Raman process in addition to the Orbach process, with the Ueff/k value of 57.5 K and the C value of 28.27 s-1K-2.14; while D-2 displays dual magnetic relaxation behavior at 0 Oe field, with the Ueff/k value 114.8 K for the slow relaxation process (SR) and the C value of 10.656 s-1K-5.80 for the fast relaxation process (FR), respectively. Theoretical calculations indicated that the conjugated groups (phenyl vs naphthyl) of the Schiff base bridging ligands (H2L1 and H2L2) significantly affect the intramolecular magnetic interactions between the Dy3+ ions and ultimately lead to different relaxations. Furthermore, magnetic circular dichroism (MCD) measurements showed that these two pairs of Dy4 enantiomers exhibit strong room temperature magneto-optical Faraday effects; notably, increasing the conjugated group on the Schiff base bridging ligand is beneficial to enhancing the magneto-optical Faraday effects.

Actinide-lanthanide single electron metal-metal bond formed in mixed-valence di-metallofullerenes.

Understanding metal-metal bonding involving f-block elements has been a challenging goal in chemistry. Here we report a series of mixed-valence di-metallofullerenes, ThDy@C2n (2n = 72, 76, 78, and 80) and ThY@C2n (2n = 72 and 78), which feature single electron actinide-lanthanide metal-metal bonds, characterized by structural, spectroscopic and computational methods. Crystallographic characterization unambiguously confirmed that Th and Y or Dy are encapsulated inside variably sized fullerene carbon cages. The ESR study of ThY@D3h(5)-C78 shows a doublet as expected for an unpaired electron interacting with Y, and a SQUID magnetometric study of ThDy@D3h(5)-C78 reveals a high-spin ground state for the whole molecule. Theoretical studies further confirm the presence of a single-electron bonding interaction between Y or Dy and Th, due to a significant overlap between hybrid spd orbitals of the two metals.

Slow magnetic relaxation in 8-coordinate Mn(II) compounds.

The design and synthesis of high-spin Mn(II)-based single-molecule magnets (SMMs) have not been well developed to a great extent, as compared with a large number of SMMs based on the other first row transition metal complexes. In light of our success in designing Fe(II), Co(II) and Fe(III)-based SMMs with a high coordination number of 8, it is of great interest to design Mn(II) analogues with such a strategy. In this contribution, four Mn(II) compounds, [MnII(Ln)2](ClO4)2 (1-4) were obtained from reactions of neutral tetradentate ligands, L1-L4, with hydrated MnII(ClO4)2 (L1 = 2,9-bis(carbomethoxy)-1,10-phenanthroline, L2 = 2,9-bis(carbomethoxy)-2,2'-dipyridine, L3 = N2,N9-dibutyl-1,10-phenanthroline-2,9-dicarboxamide, L4 = 6,6'-bis(2-(tert-butyl)-2H-tetrazol-5-yl)-2,2'-bipyridine). Their crystal structures have been determined by X-ray crystallography and it clearly shows that the Mn(II) centers in these compounds have an oversaturated coordination number of 8. Their magnetic properties have been investigated in detail; to our surprise, all of these Mn(II) compounds show interesting slow magnetic relaxation behaviors under an applied direct current field, although they have very small negative D values.

Two-Electron Oxidations at a Single Cerium Center.

Two-electron oxidations are ubiquitous and play a key role in the synthesis and catalysis. For transition metals and actinides, two-electron oxidation often takes place at a single-metal site. However, redox reactions at rare-earth metals have been limited to one-electron processes due to the lack of accessible oxidation states. Despite recent advancements in nontraditional oxidation state chemistry, the low stability of low-valent compounds and large disparity among different oxidation states prevented the implementation of two-electron processes at a single rare-earth metal center. Here we report two-electron oxidations at a cerium(II) center to yield cerium(IV) terminal oxo and imido complexes. A series of cerium(II-IV) complexes supported by a tripodal tris(amido)arene ligand were synthesized and characterized. Experimental and theoretical studies revealed that the cerium(II) complex is best described as a 4f2 ion stabilized by δ-backdonation to the anchoring arene, while the cerium(IV) oxo and imido complexes exhibit multiple bonding characters. The accomplishment of two-electron oxidations at a single cerium center brings a new facet to molecular rare-earth metal chemistry.

Tunable Chromic Properties of Viologen-Metal Polymers Modulated by Coordination Modes for Inkless Erasable Printing.

Inkless and erasable printing (IEP) based on chromic materials holds great promise to alleviate environmental and sustainable problems. Metal-organic polymers (MOPs) are bright platforms for constructing IEP materials. However, it is still challenging to design target MOPs with excellent specific functions rationally due to the intricate component-structure-property relationships. Herein, an effective strategy was proposed for the rational design IEP-MOP materials. The stimuli-responsive viologen moiety was introduced into the construction of MOPs to give it potential chromic behaviors and two different coordination models (i. e. bilateral coordination model, M1 ; unilateral coordinated model, M2 ) based on the same viologen ligand were designed. Aided by theoretical calculations, model M1 was recommended secondarily as a more suitable system for IEP materials. Along this line, two representative viologen-ZnII MOPs 1 and 2 with models M1 and M2 were synthesized successfully. Experiments exhibit that 1 does have quicker stimuli response, stronger color contrast and longer radical lifetime compared to 2. Significantly, the obtained 1-IEP media brightly inherits the excellent chromic characteristics of 1 and the flexibility of the paper at the same time, which achieves most daily printing requirements, as well as enough resolution and durability to be used in identification by smart device.

Accessing five oxidation states of uranium in a retained ligand framework.

Understanding and exploiting the redox properties of uranium is of great importance because uranium has a wide range of possible oxidation states and holds great potential for small molecule activation and catalysis. However, it remains challenging to stabilise both low and high-valent uranium ions in a preserved ligand environment. Herein we report the synthesis and characterisation of a series of uranium(II-VI) complexes supported by a tripodal tris(amido)arene ligand. In addition, one- or two-electron redox transformations could be achieved with these compounds. Moreover, combined experimental and theoretical studies unveiled that the ambiphilic uranium-arene interactions are the key to balance the stabilisation of low and high-valent uranium, with the anchoring arene acting as a δ acceptor or a π donor. Our results reinforce the design strategy to incorporate metal-arene interactions in stabilising multiple oxidation states, and open up new avenues to explore the redox chemistry of uranium.

Piezochromism and Conductivity Modulations under High Pressure by Manipulating the Viologen Radical Concentration.

Manipulating the radical concentration to modulate the properties in solid multifunctional materials is an attractive topic in various frontier fields. Viologens have the unique redox capability to generate radical states through reversible electron transfer (ET) under external stimuli. Herein, taking the viologens as the model, two kinds of crystalline compounds with different molecule-conjugated systems were designed and synthesized. By subjecting the specific model viologens to pressure, the cross-conjugated 2-X all exhibit much higher radical concentrations, along with more sensitive piezochromic behaviors, compared to the linear-conjugated 1-X. Unexpectedly, we find that the electrical resistance (R) of 1-NO3 decreased by three orders of magnitude with the increasing pressure, while that in high-radical-concentration 2-NO3 remained almost unchanged. To date, such unusual invariant conductivity has not been documented in molecular-based materials under high pressure, breaking the conventional wisdom that the generations of radicals are beneficial to improve conductivity. We highlight that adjusting the molecular conjugation modes can be used as an effective way to regulate the radical concentrations and thus modulate properties rationally.

Adaptability to Crystal Fields in a Series of COT/Monodentate Ligand-Based Dy and Er Single Ion Magnets.

Herein, DyIII and ErIII, the typical oblate and prolate Kramers Ln ions, were employed to synthesize a series of isostructural pairs: 2-5Ln (Ln = Dy and Er). In the [(COT)Ln(THF)4]+ cationic fragments of 2Ln, central ions were coordinated by the equatorial ligand cyclooctatetraenyl (COT) and THF solvents, while in the heteroleptic complexes 3Ln ((COT)Ln(OAr')), 4Ln ((COT)Ln(OAr″)), and 5Ln ((COT)Ln(N††)), the coordination geometries were formed by the cooperation of COT and bulky aryloxides OAr' (2,6-bis(diphenylmethyl)-4-methylphenyl), OAr″ (2,6-bis(1-adamantyl)-4-methylphenyl), and amide N†† (bis(triisopropylsilyl) amide) for 3Ln, 4Ln, and 5Ln, respectively. Among these complexes, with the combinations of varying coordination geometries and different anisotropies of f orbitals, 2Er, 3Dy, and 4Dy were found to be zero-field SIMs with effective energy barriers of 181.9, 527.7, and 622.0 K, respectively, which are consistent with the structural analyses and ab initio calculations. The blocking temperatures (TB) of 3Dy and 4Dy are 4 and 7 K, respectively, as confirmed by the hysteresis loops at varying temperatures. The structures of 5Ln exhibit an almost perfect umbrella-shaped geometry, characterized by N-Ln-Centroid (COT) angles measuring 178.9 and 179.3° for 5Dy and 5Er, respectively. Crystallographic data from these structures were utilized to investigate the impact of ligand alignment on the magnetic properties of the compounds.

Circularly polarized luminescence and magneto-optic effects from chiral Dy(III) single molecule magnets.

A new pair of multifunctional Zn(II)-Dy(III) enantiomers based on the chiral Schiff-base ligands [R,R-ZnLDy(H2O)(NO3)3] (1R2R-ZnDy) and [S,S-ZnLDy(H2O)(NO3)3] (1S2S-ZnDy) (H2L = phenol, 2,2'-[[(1R,2R/1S,2S)-1,2-diphenyl-1,2-ethanediyl]bis[(E)-nitrilomethylidyne]]bis[6-methoxy]) was synthesized and characterized. Magnetic studies indicate that 1R2R-ZnDy behaves as a single-molecule magnet. Enantiomers 1R2R-ZnDy and 1S2S-ZnDy show chiroptical activity and circularly polarized luminescence in the N,N-dimethylformamide (DMF) solution. The chiral Zn(II)-Dy(III) complexes display magnetic circular dichroism signals at room temperature. Accordingly, these complexes will inspire intriguing research on single-molecule magnets with circular polarization of luminescence activity and magneto-optic effects, which will give new clues to design multifunctional molecular magnetic materials.

A phase III randomized, double-blind, placebo-controlled trial of the denosumab biosimilar QL1206 in postmenopausal Chinese women with osteoporosis and high fracture risk.

The current study evaluated the efficacy and safety of a denosumab biosimilar, QL1206 (60 mg), compared to placebo in postmenopausal Chinese women with osteoporosis and high fracture risk. At 31 study centers in China, a total of 455 postmenopausal women with osteoporosis and high fracture risk were randomly assigned to receive QL1206 (60 mg subcutaneously every 6 months) or placebo. From baseline to the 12-month follow-up, the participants who received QL1206 showed significantly increased bone mineral density (BMD) values (mean difference and 95% CI) in the lumbar spine: 4.780% (3.880%, 5.681%), total hip :3.930% (3.136%, 4.725%), femoral neck 2.733% (1.877%, 3.589%) and trochanter: 4.058% (2.791%, 5.325%) compared with the participants who received the placebo. In addition, QL1206 injection significantly decreased the serum levels of C-terminal crosslinked telopeptides of type 1 collagen (CTX): -77.352% (-87.080%, -66.844%), and N-terminal procollagen of type l collagen (P1NP): -50.867% (-57.184%, -45.217%) compared with the placebo over the period from baseline to 12 months. No new or unexpected adverse events were observed. We concluded that compared with placebo, QL1206 effectively increased the BMD of the lumbar spine, total hip, femoral neck and trochanter in postmenopausal Chinese women with osteoporosis and rapidly decreased bone turnover markers. This study demonstrated that QL1206 has beneficial effects on postmenopausal Chinese women with osteoporosis and high fracture risk.

Effects of Counterions, Coordination Anions, and Coordination Solvent Molecules on Single-Molecule Magnetic Behaviors and Nonlinear Optical Properties of Chiral Zn2Dy Schiff Base Complexes.

By changing the counterions (ClO4- and CF3SO3-) and the coordination anions (Cl- and Br-), we investigated their influences on the structures and performances of a class of Zn2Dy chiral single-molecule magnets (SMMs), which are based on a pair of chiral Schiff bases R,R-H2LSchiff and S,S-H2LSchiff {R,R-H2LSchiff = 2-((E)-((1R,2R)-2-((E)-2-hydroxy-3-methoxybenzylideneamino)cyclohexylimino)methyl)-6-methoxyphenol and S,S-H2LSchiff = 2-((E)-((1S,2S)-2-((E)-2-hydroxy-3-methoxybenzylideneamino)cyclohexylimino)methyl)-6-methoxyphenol}. Three pairs of chiral Zn2Dy Schiff base complexes were obtained by directed synthesis, which are [DyZn2(R,R-LSchiff)Cl2(H2O)](ClO4)·0.5MeOH·0.25H2O (R-1) and [DyZn2(S,S-LSchiff)Cl2(H2O)][DyZn2(S,S-LSchiff)Cl2(MeOH)](ClO4)2·MeOH·0.5H2O (S-1), [DyZn2(R,R-LSchiff)Cl2(H2O)](CF3SO3)·0.5MeOH (R-2) and [DyZn2(S,S-LSchiff)Cl2(H2O)][DyZn2(S,S-LSchiff)Cl2(MeOH)](CF3SO3)2·MeOH (S-2), and [DyZn2(R,R-LSchiff)Br2(H2O)](CF3SO3)·0.25MeOH (R-3) and [DyZn2(S,S-LSchiff)Br2(H2O)][DyZn2(S,S-LSchiff)Br2(MeOH)](CF3SO3)2 (S-3). They all exhibit good SMM behaviors, and their magnet relaxation is regulated by not only the counterions (ClO4- and CF3SO3-) but also the coordination anions (Cl- and Br-); these anions also have important effects on the second-harmonic generation (SHG) and third harmonic generation (THG) nonlinear optical properties. Interestingly, in the S-configuration complexes, the coordination solvent molecule of the Dy3+ ion on half of the molecules is the methanol molecule instead of the water molecule. This change in the coordinating solvent molecule can also significantly affect the SMM behaviors and the SHG and THG nonlinear optical properties. Moreover, ab initio calculations were applied to rationally explain the SMM properties.

Chain Length Modulated Dimerization and Cyclization of Terminal Thienyl-Blocked Oligopyrranes.

Oxidation of thienyl-blocked bilane and pentapyrrane afforded chain length dependent products of the symmetric dimer D1 and the thienyloligopyrrin-appended pentaphyrin analogue P2, respectively, with the latter formed by simultaneous dimerization and cyclization. Coordination of D1 and P2 with Cu(II) afforded di- and monometallic complexes D1-Cu2 and P2-Cu, respectively. These compounds exhibit distinct NIR absorption, with the absorption tail of D1-Cu2 extended to ca. 1900 nm despite its smaller conjugation framework than that of P2-Cu.

Unprecedented Ferroelectricity and Ferromagnetism in a Cr2+ -Based Two-Dimensional Hybrid Perovskite.

Organic-inorganic hybrid perovskites (OIHPs) have gained tremendous interest for their rich functional properties. However, the coexistence of more than one of ferroelectricity, ferromagnetism and ferroelasticity has been rarely found in OIHPs. Herein, we report a two-dimensional Cr2+ -based OIHP, [3,3-difluorocyclobutylammonium]2 CrCl4 ([DFCBA]2 CrCl4 ), which shows both ferroelectricity and ferromagnetism. It undergoes a 4/mmmFm type ferroelectric phase transition at a temperature as high as 387 K and shows multiaxial ferroelectricity with a saturate polarization of 2.1 µC cm-2 . It acts as a soft ferromagnet with a Curie temperature of 32.6 K. This work throws light on the exploration of OIHPs with the coexistence of ferroelectricity and ferromagnetism for applications in future multifunctional smart devices.

Bioinspired Design of seco-Chlorin Photosensitizers to Overcome Phototoxic Effects in Photodynamic Therapy.

Photodynamic therapy (PDT) is a non-invasive treatment modality against a range of cancers and nonmalignant diseases, however one must be aware of the risk of causing phototoxic reactions after treatment. We herein report a bioinspired design of next-generation photosensitizers (PSs) that not only effectively produce ROS but undergo fast metabolism after treatment to overcome undesirable side effects. We constructed a series of ß-pyrrolic ring-opening seco-chlorins, termed beidaphyrin (BP), beidapholactone (BPL), and their zinc(II) derivatives (ZnBP and ZnBPL), featuring intense near-infrared absorption and effective O2 photosensitization. Irradiation of ZnBPL led to a non-cytotoxic, metabolizable beidaphodiacetamide (ZnBPD) via in situ generated O2.- but not 1 O2 , as revealed by mechanistic studies including time-resolved absorption, kinetics, and isotope labeling. Furthermore, water-soluble ZnBPL showed an effective therapeutic outcome, fast metabolism, and negligible phototoxic reactions.

Slow magnetic relaxation in high-coordinate Co(II) and Fe(II) compounds bearing neutral tetradentate ligands.

The first-row transition metal compounds, [MII(L1)2](ClO4)2 (M = Ni (1); Co (2)), have been prepared by treatment of a neutral tetradentate ligand (L1 = N2,N9-dibutyl-1,10-phenanthroline-2,9-dicarboxamide) with metal perchlorate salts in MeOH. Both compounds have been structurally characterized by X-ray crystallography and it was found that the coordination numbers are 6 and 7, respectively. The reaction of 6,6'-bis(2-tbutyl-tetrazol-5-yl)-2,2'-bipyridine (L2) with hydrated FeII(ClO4)2 afforded a 8-coordinate Fe(II) compound, [FeII(L2)2](ClO4)2 (3); however its reaction with hydrated CoII(ClO4)2 resulted in 6-coordinate [CoII(L2)2](ClO4)2. It is interesting to observe field-induced slow magnetic relaxation in the 7-coordinate Co(II) compound 2 and 8-coordinate Fe(II) compound 3, which further supports the validity of designing high coordination number compounds as single-molecule magnets. Direct current magnetic studies demonstrate that 2 has a very large positive D value (56.2 cm-1) and a small E value (0.66 cm-1), indicating easy plane magnetic anisotropy. Consistent with the larger D value, an effective spin-reversal barrier of Ueff = 100 K (71.4 cm-1) is obtained, which is the highest value reported for 7-coordinate Co(II) complexes with a pentagonal bipyramidal geometry. In contrast, 8-coordinate Fe(II) compound 3 exhibits uniaxial magnetic anisotropy.

Coexistence of magnetic and electric orderings in a divalent Cr2+-based multiaxial molecular ferroelectric.

Multiferroic materials have attracted great interest because of their underlying new science and promising applications in data storage and mutual control devices. However, they are still very rare and highly imperative to be developed. Here, we report an organic-inorganic hybrid perovskite trimethylchloromethylammonium chromium chloride (TMCM-CrCl3), showing the coexistence of magnetic and electric orderings. It displays a paraelectric-ferroelectric phase transition at 397 K with an Aizu notation of 6/mFm, and spin-canted antiferromagnetic ordering with a Néel temperature of 4.8 K. The ferroelectricity originates from the orientational ordering of TMCM cations, and the magnetism is from the [CrCl3]- framework. Remarkably, TMCM-CrCl3 is the first experimentally confirmed divalent Cr2+-based multiferroic material as far as we know. A new category of hybrid multiferroic materials is pointed out in this work, and more Cr2+-based multiferroic materials will be expectedly developed in the future.

Homochiral Ferromagnetic Coupling Dy2 Single-Molecule Magnets with Strong Magneto-Optical Faraday Effects at Room Temperature.

By the bridging action of the 6-chloro-2-hydroxypyridine (Hchp) ligand and the terminal coordination role of the homochiral ligand, (-)/(+)-3-trifluoroacetyl camphor (l-Htfc/d-Htfc), a pair of enantiomerically pure dysprosium(III) dinuclear complexes, [Dy2(l-tfc)4(chp)2(MeOH)2] (l-1) and [Dy2(d-tfc)4(chp)2(MeOH)2] (d-1), was obtained. Their circular dichroism (CD) spectra verified their enantiomeric nature. Magnetic investigation indicated that they exhibit ferromagnetic interaction and good zero field single-molecule magnet (SMM) properties. The Ueff/k values of l-1 and d-1 at 0 Oe are 180.5 and 181.3 K, respectively, which are large values for homochiral Dy(III) SMMs. A reasonable explanation for the magnetic properties of l-1 and d-1 was supplied by ab initio calculations. Remarkably, magnetic circular dichroism (MCD) investigation revealed that the chiral Dy2 enantiomers show a strong magneto-optical Faraday effect at room temperature, suggesting potential applications in magneto-optical devices.

Slow magnetic relaxation in structurally similar mononuclear 8-coordinate Fe(II) and Fe(III) compounds.

A pair of structurally-similar and stable 8-coordinate high-spin Fe(ii) and Fe(iii) compounds have been obtained. Both compounds exhibit field-induced slow magnetic relaxation behaviour. The Fe(iii) compound represents the first example of 8-coordinate Fe(iii) single-molecule magnets (SMM).