Redox Activity of IrIII Complexes with Multidentate Ligands Based on Dipyrido-Annulated N-Heterocyclic Carbenes: Access to High Valent and High Spin State with Carbon Donors

Synthetic strategies to access high-valent iridium complexes usually require use of π donating ligands bearing electronegative atoms (e. g. amide or oxide) or σ donating electropositive atoms (e. g. boryl or hydride). Besides the η5 -(methyl)cyclopentadienyl derivatives, high-valent η1 carbon-ligated iridium complexes are challenging to synthesize. To meet this challenge, this work reports the oxidation behavior of an all-carbon-ligated anionic bis(CCC-pincer) IrIII complex. Being both σ and π donating, the diaryl dipyrido-annulated N-heterocyclic carbene (dpa-NHC) IrIII complex allowed a stepwise 4e- oxidation sequence. The first 2e- oxidation led to an oxidative coupling of two adjacent aryl groups, resulting in formation of a cationic chiral IrIII complex bearing a CCCC-tetradentate ligand. A further 2e- oxidation allowed isolation of a high-valent tricationic complex with a triplet ground state. These results close a synthetic gap for carbon-ligated iridium complexes and demonstrate the electronic tuning potential of organic π ligands for unusual electronic properties.

Inorganic Chain Mediated Excitonic Properties in One-Dimensional Lead Halide Hybrid Perovskites

Semiconductors that emit intrinsic white light are considered next-generation lighting sources. Herein, the broadband emission of one-dimensional (1D) lead halide perovskites, TMAPbBr_3-xI_x (x = 0, 1, 1.5, 2, 3; TMA⁺ = tetramethylammonium), is systematically investigated. Lattice distortion causes the conversion of dark excitons to bright self-trapped excitons. Owing to its strongly localized exciton recombination and high absorption probability, TMAPbBr₃ is the most viable in this family. A delocalized hole increases the nonradiative recombination rate of excitons in TMAPbBr_3-xI_x alloys. In 1D TMAPbBr_3-xI_x perovskites, the vibration mode of the Pb-X bond stretching of the PbX₆ octahedra contributes more to the effect on exciton-phonon coupling than the mode of the X-Pb-X angle bending. Pb-X bond stretching and spontaneous polarization can tune exciton binding energy. This systematic study of excitonic behavior in 1D compounds relates the nature of ground states to the unknown excited states and provides the rational design of materials with stable and efficient broadband emission.

Fluoride-bridged dinuclear dysprosium complex showing single-molecule magnetic behavior: supramolecular approach to isolate magnetic molecules

Using Na-encapsulated benzo[18]crown-6 (Na)(B18C6) as a counter cation, we successfully magnetically isolated a fluoride-bridging Dy dinuclear complex {[(PW₁₁O₃₉)Dy(H₂O)₂]₂F} (Dy₂POM) with lacunary Keggin ligands. (Na)(B18C6) formed two types of tetramers through C-H⋯O, π⋯π and C-H⋯π interactions, and each tetramer aligned in one dimension along the c-axis to form two types of channels. One channel was partially penetrated by a supramolecular cation from the ±a-axis direction, dividing the channel in the form of a "bamboo node". Dy₂POM was spatially divided by this "bamboo node," which magnetically isolated one portion from the other. The temperature dependence of the magnetic susceptibility indicated a weak ferromagnetic interaction between the Dy ions bridged by fluoride. Dy₂POM exhibited the magnetic relaxation characteristics of a single-molecule magnet, including the dependence of AC magnetic susceptibility on temperature and frequency. Magnetic relaxation can be described by the combination of thermally active Orbach and temperature-independent quantum tunneling processes. The application of a static magnetic field effectively suppressed the relaxation due to quantum tunneling.

Ferroelastic-like transition and solvents affect the magnetism of a copper-organic radical one-dimensional coordination polymer

The one-dimensional coordination polymers {[Cu^II(hfac)₂]₃(m-BNN)}_n·nCH₂Cl₂ (1·CH₂Cl₂, P1̄) and {[Cu^II(hfac)₂]₃(m-BNN)}_n (1', P2/n), hfac = hexafluoroacetylacetonate and m-BNN = meta-phenylene bis(nitronyl-nitroxide), were obtained from CH₂Cl₂ and CHCl₃, respectively. 1·CH₂Cl₂ is transformed to 1 at 335 K. Their magnetic susceptibilities differ in both magnitude and temperature dependence behavior. 1 and 1' undergo a ferroelastic-like phase transition at 110 K and an unidentified one at 37 K. There is a subtle long relaxation of this ferroelastic-like ordered state.

Slider-crank mechanism in a molecular crystal: conversion of linear thermal expansion of a lattice to circular rotation of a coordination chain

Slider-crank like force conversion of linear thermal expansion to rotational motion of the coordination chains were observed in the molecular crystal.

Structural Phase Transitions of a Molecular Metal Oxide

The structural phase of a metal oxide changes with temperature and pressure. During phase transitions, component ions move in multidimensional metal-oxygen networks. Such macroscopic structural events are robust to changes in particle size, even at scales of around 10 nm, and size effects limiting these transitions are particularly important in, for example, high-density memory applications of ferroelectrics. In this study, we examined structural transitions of the molecular metal oxide [Na@(SO₃ )₂ (n-BuPO₃ )₄ Mo^V ₄ Mo^VI ₁₄ O₄₉ ]^5- (Molecule 1) at approximately 2 nm by using single-crystal X-ray diffraction analysis. The Na⁺ encapsulated in the discrete metal-oxide anion exhibited a reversible order-disorder transition with distortion of the Mo-O molecular framework induced by temperature. Similar order-disorder transitions were also triggered by chemical pressure induced by removing crystalline solvent molecules in the single-crystal state or by substituting the countercation to change the molecular packing.

Publisher Correction: Metallofullerenes: Welcome to the single-molecule electret device

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Doping of metal-free molecular perovskite with hexamethylenetetramine to create non-centrosymmetric defects

The metal-free perovskite (dabcoH₂²⁺)(NH₄)Br (d-Br) (dabco: 1,4-diazabicyclo[2.2.2]octane) was doped with non-centrosymmetric hexamethylenetetramine.

Ligand Structure Effects on Molecular Assembly and Magnetic Properties of Copper(II) Complexes with 3-Pyridyl-Substituted Nitronyl Nitroxide Derivatives

Reaction of Cu(hfac)₂ with methyl- and bromo-3-pyridyl-substituted nitronyl nitroxides (L ^R ) leads to assemble a diverse set of coordination complexes: mononuclear [Cu(hfac)₂L ^2-Me ], binuclear [{Cu(hfac)₂}₂(H₂O)L ^2-Me ], trinuclear [{Cu(hfac)₂}₃(L ^6-Br )₂], pentanuclear [{Cu(hfac)₂}₅(L ^2-Me )₂], and [{Cu(hfac)₂}₅(L ^2-Me )₄], cocrystals [Cu(hfac)₂(L ^2-Br )₂]·[Cu(hfac)₂(H₂O)₂] and [Cu(hfac)₂(L ^2-Br )₂]·2[Cu(hfac)₂H₂O], one-dimensional polymers [Cu(hfac)₂L ^2-Br ] _n and [Cu(hfac)₂L ^6-Br ] _n , and cyclic dimers [Cu(hfac)₂L ^5-Me ]₂, [Cu(hfac)₂L ^5-Br ]₂, and [Cu(hfac)₂L ^6-Me ]₂. The molecular structures of the obtained complexes are strongly affected by the substituent type and its location in the pyridine heterocycle. Occupation of the second position of the pyridine ring increases the steric hindrance of both imine and nitroxide coordination sites of L ^2-R , which is favorable for the formation of various conformers and precipitation of complexes with different molecular structures. The pentanuclear [{Cu(hfac)₂}₅(L ^2-Me )₂] and [{Cu(hfac)₂}₅(L ^2-Me )₄] complexes do not have prior analogues and are valuable model objects for investigation of the mechanism of formation of various coordination polymers. The arrangement of long Cu-O_NO bonds in {CuO₆} square bipyramids due to the weakening nitroxide donor site in complexes, based on L ^2-Me , L ^2-Br , and L ^6-Br ligands, results in ferromagnetic exchange interactions between spins of Cu²⁺ ions and nitroxides. Complexes with substituents that do not considerably affect the coordination ability of ligands (L ^5-Me , L ^5-Br , and L ^6-Me ) exhibit strong antiferromagnetic exchange interactions between spins of Cu²⁺ ions and nitroxides.

Pressure-Controlled Migration of Paramagnetic Centers in a Heterospin Crystal

A study of the single-crystal-to-single-crystal transformation induced by temperature variation for the chain polymer Cu(II) complex with nitronyl nitroxide showed that an increase in the hydrostatic pressure of up to ∼0.07 GPa completely changes the intracrystalline displacements of molecules relative to one another. This, in turn, significantly affects the interaction energy of the unpaired electrons of the paramagnetic centers and hence the form of the temperature dependence of the magnetic susceptibility χT. The cooling of crystals under normal conditions causes a rearrangement of the intrachain exchange clusters {>N-•O-Cu(II)-O•-N<} accompanied by a shortening of the distances between the paramagnetic centers. This changes the character of exchange interactions and generates multistage spin transitions. An increase in the hydrostatic pressure leads to a drastic change in the O···O distances between the nitroxyl fragments of adjacent chains, an increase in the antiferromagnetic exchange between them, and complete suppression of spin transitions.

Selective Ion Exchange in Supramolecular Channels in the Crystalline State

Artificial ion channels are of increasing interest because of potential applications in biomimetics, for example, for realizing selective ion permeability through the transport and/or exchange of selected ions. However, selective ion transport and/or exchange in the crystalline state is rare, and to the best of our knowledge, such a process has not been successfully combined with changes in the physical properties of a material. Herein, by soaking single crystals of Li₂ ([18]crown-6)₃ [Ni(dmit)₂ ]₂ (H₂ O)₄ (1) in an aqueous solution containing K⁺ , we succeeded in complete ion exchange of the Li⁺ ions in 1 with K⁺ ions in the solution, while maintaining the crystalline state of the material. This ion exchange with K⁺ was selectively conducted even in mixed solutions containing K⁺ as well as Na⁺ /Li⁺ . Furthermore, remarkable changes in the physical properties of 1 resulted from the ion exchange. Our finding enables not only the realization of selective ion permeability but also the development of highly sensitive biosensors and futuristic ion exchange agents, for example.

Structural, Optical, Magnetic, and Dielectric Properties in Hybrid Solid Solutions of ZnαNi1-α(en)3Ag2I4 (0 < α < 1) by Varying the Relative Zn/Ni Content

The hybrids of M(en)₃Ag₂I₄ (M = Zn or Ni) are isostructural to each other and crystallize in space group P6₃22 with quite similar lattice parameters. The hybrid solid solutions Zn_αNi_1-α(en)₃Ag₂I₄ (0 < α < 1) have been prepared via self-assembly in the mixed N,N-dimethylformamide solution of AgNO₃, KI, and ethylenediamine, meanwhile, with certain relative amount of [Zn(en)₃]²⁺ and [Ni(en)₃]²⁺ ions at ambient condition. All hybrid solid solutions are isostructural to the parent hybrids M(en)₃Ag₂I₄ (M = Zn or Ni). The UV-vis-near IR diffuse reflection spectra in solid state, thermogravimetric analysis, variable-temperature magnetic susceptibility, and dielectrics have been investigated for Zn_αNi_1-α(en)₃Ag₂I₄ (0 < α < 1). The intensity of bands centered at 540 and 860 nm in UV-vis-near IR spectra, arising from the d-d electron transition in Ni²⁺ ion, as well as the Curie constant decreases linearly with the molar fraction of Zn (α)/Ni (1 - α), whereas the c-axis length, the C-N and C-C bond lengths in the ethylenediamine, the frequency-independent dielectric permittivity and the onset temperature of dielectric relaxation, and so forth show nonmonotonical alternation with the fraction of Zn (α)/Ni (1 - α) in the solid solution, and the origin for these differences is further discussed.

Preparation of Preyssler-type Phosphotungstate with One Central Potassium Cation and Potassium Cation Migration into the Preyssler Molecule to form Di-Potassium-Encapsulated Derivative

A mono-potassium cation-encapsulated Preyssler-type phosphotungstate, [P₅W₃₀O₁₁₀K]^14- (1), was prepared as a potassium salt, K₁₄[P₅W₃₀O₁₁₀K] (1a), by heating mono-bismuth- or mono-calcium-encapsulated Preyssler-type phosphotungstates (K₁₂[P₅W₃₀O₁₁₀Bi(H₂O)] or K₁₃[P₅W₃₀O₁₁₀Ca(H₂O)]) in acetate buffer. Characterization of the potassium salt 1a by single-crystal X-ray structure analysis, ³¹P and ¹⁸³W nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy, high-resolution electrospray ionization mass spectroscopy, and elemental analysis revealed that one potassium cation is encapsulated in the central cavity of the Preyssler-type phosphotungstate molecule with a formal D _5h symmetry. Density functional theory calculations have confirmed that the potassium cation prefers the central position of the cavity over a side position, in which no water molecules are coordinated to the encapsulated potassium cation. ³¹P NMR and cyclic voltammetry analyses revealed the rapid protonation-deprotonation of the oxygens in the cavity compared to that of other Preyssler-type compounds. Heating of 1a in the solid state afforded a di-K⁺-encapsulated compound, K₁₃[P₅W₃₀O₁₁₀K₂] (2a), indicating that a potassium counter-cation is introduced in one of the side cavities, concomitantly displacing the internal potassium ion from the center to a second side cavity, thus providing a new method to encapsulate an additional cation in Preyssler compounds.

Synthesis, crystal structures and magnetic properties of six coordination compounds constructed with pyridine iminomethyl–TEMPO radicals and [M(hfac)2] (M = CuII and MnII)

We describe the crystal structures and magnetic properties of six coordination metal-(R-Py-iminomethyl-TEMPO) radical compounds.

Chemo-chromism in an orthogonal dabco-based Co(ii) network assembled by methanol-coordination and hydrogen bond formation

A newly prepared Co-based complex showed chromism by desorption of a coordinative solvent. Structural details and desorption/adsorption processes are discussed in depth.

(Azulene-1,3-diyl)-bis(nitronyl nitroxide) and (Azulene-1,3-diyl)-bis(iminonitroxide) and Their Copper Complexes

In contrast to diradicals connected by alternant hydrocarbons, only a few studies on those connected by nonalternant hydrocarbons have been reported. The syntheses, structures, and magnetic properties of azulene-1,3-diyl linked bis(nitronyl nitroxide) (NN₂ Az) and bis(iminonitroxide) (IN₂ Az) diradicals and their Cu(hfac)₂ (hfac=hexafluoroacetylacetonate) complexes were investigated. NN₂ Az was shown to have an intramolecular ferromagnetic interaction with J_obs /k_B =+10.0 K (H=-2JS₁ ⋅S₂ ) between (nitronyl nitroxide) spins, whereas IN₂ Az was estimated to have a much weaker intramolecular magnetic interaction. The reactions of NN₂ Az and IN₂ Az with Cu(hfac)₂ gave a 1:2 [{Cu(hfac)₂ }₂ (NN₂ Az)] complex and a 1:1 [Cu(hfac)₂ (IN₂ Az)]⋅C₆ H₁₂ complex, respectively. [{Cu(hfac)₂ }₂ (NN₂ Az)] showed strong intramolecular antiferromagnetic interactions (J_1-Cu-R /k_B ≈-800 K, J_2-Cu-R /k_B ≈-500 K) between the Cu^II spins and the coordinating NN spins, whereas [Cu(hfac)₂ (IN₂ Az)] exhibited a ferromagnetic exchange interaction (J_obs-Cu-R /k_B =+114 K) between the Cu^II spin and the imino-coordinated iminonitroxide spin.

Associated factors of behavioural problems in children at preschool age: the Hokkaido study on environment and children's health

BACKGROUND

Finding associated factors with childhood behavioural problems as early as preschool age is important. Studies have revealed several factors including socioeconomic factors, which may vary among different cultural background and population. However, investigation in general Japanese population of preschool age has not been well demonstrated. Thus, the objective of this study was to examine associated factors of childhood behavioural problems using Strengths and Difficulties Questionnaire (SDQ) in a prospective birth cohort study.

METHODS

Total 3813 SDQ were distributed between October 2014 and December 2015 to the subpopulation of prospective birth cohort study, the Hokkaido Study on Environment and Children's Health. The subpopulation consisted of participants who had reached age 5 and were born between April 2008 and December 2010. Baseline questionnaire filled at recruitment and birth record were used to obtain participant information. Children with total difficulties score ≧ 13 were defined as likelihood of behavioural problems. A total of 2553 children with valid answers were included into the analysis. The response rate was 67.1%.

RESULTS

Number of children with likelihood of behavioural problems was 521 (20.4%). Boys showed more problematic scores than girls. Multivariate analysis found that maternal pre-pregnancy BMI ≧ 30 kg/m² , primipara, maternal education lower than high school, family income during pregnancy < 3 million yen/year and boy gender were the factors associated with increased odds ratio of likelihood of child behavioural problems.

CONCLUSIONS

This study found that prenatal socioeconomic factors were associated with likelihood of child behavioural problems at preschool age in Japan.

A dielectric anomaly observed for doubly reduced mixed-valence polyoxometalate

A doubly reduced mixed-valence Keggin cluster exhibited a dielectric anomaly that originated from dipole relaxation.

Lanthanoid Template Isolation of the α-1,5 Isomer of Dicobalt(II)-Substituted Keggin Type Phosphotungstates: Syntheses, Characterization, and Magnetic Properties

A new series of heterometallic 3d-4f sandwich type phosphotungstates, [Ln{PCo2W10O38(H2O)2}2](11-) (Ln = Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III), denoted 1a-10a, respectively), have been synthesized by a one-pot reaction procedure on reacting the dilacunary K14[P2W19O69(H2O)]·24H2O precursor with Ln(NO3)3·nH2O and Co(NO3)2·6H2O in an aqueous potassium chloride solution. All the compounds were isolated as potassium salts and further characterized with different analytical techniques such as single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution electrospray ionization mass spectrometry, elemental analysis by inductively coupled plasma atomic emission spectroscopy, magnetic measurement, and thermogravimetric analysis. Single-crystal X-ray diffraction analysis of the compounds reveals that all these compounds are isostructural and crystallized in the orthorhombic crystal system in space group Iba2. The polyanions contain the α-1,5 isomer of dicobalt-substituted α-Keggin phosphotungstate, which sandwiched lanthanoid cation and formed novel heterometallic dimer species. The temperature-dependent magnetic susceptibilities of 1a, 2a, 4a, and 7a-10a indicate the dominant contribution of the ferromagnetic interaction between Co(II) and Co(II) within the cluster, while the antiferromagnetic interaction between Co(II) and Ln(III) dominates for 3a, 5a, and 6a. The isothermal magnetizations of 1a-10a show a gradual increase in magnetization at low fields and do not reach saturation even at 50 kOe.

Synthesis, Crystal Structure, and Magnetic Properties of a Chiral Cyanide-Bridged Bimetallic Framework K3[Mn(II)(L-asp)]6[Cr(III)(CN)6]·2H2O

All five coordinating atoms of the amino-acid dianion L-aspartate (L-asp = NH2CH(COO)CH2COO(2-)) are found to be involved in coordination with Mn(II) in the presence of [Cr(III)(CN)6](3-) to self-assemble into a chiral three-dimensional cyanide-bridged K3[Mn(L-asp)]6[Cr(CN)6]·2H2O containing the highest ratio of Mn:Cr of 6:1. It adopts the chiral P3 (no. 143) space group consisting of zigzag Mn-OCO-Mn chains sharing edges of hexagonal channels with central [Cr(CN)6](3-), while K(+) and H2O occupy another parallel star-shaped channel. Its magnetic susceptibility above 100 K is dominated by the nearest neighbor (Mn-Cr at 5.08 and 5.31 Å) antiferromagnetic (AF) exchange interactions (θ = -15(1) K) and below 40 K by further AF interaction between Mn and Mn at 5.32 Å. It finally reaches a steady value at 4.5 K, where a bifurcation of the zero-field-cooled and field-cooled magnetizations is observed in small fields (<1 kOe). The isothermal magnetization is linear in field and deviating toward saturation above 60 kOe at 2 K. No imaginary component of the ac susceptibilities is observed. This behavior is associated with long-range antiferromagnetic order of a helical or conic nature where the magnetic sublattices are numerous [2n × (6Mn + 1Cr)], leading to a domain of sufficient size to allow for the presence of the bifurcation. A model is proposed based on the local anisotropy and symmetry multiplicity of the space group.

Characteristic responses of a phospholipid molecular layer to polyols

Polyols (sugar alcohols) are widely used in foods, pharmaceutical formulations and cosmetics, and therefore it is important to understand their effects on cell membranes and skin. To address this issue, we examined the effect of polyols (1,2-ethanediol (ethylene glycol), 1,3-butanediol, 1,2,3-propanetriol (glycerol), and 1,2,3,4-butanetetraol) on artificial membrane systems (liposomes, monolayers, or dry films) prepared from phospholipid (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)). 1,2-Ethanediol and 1,3-butanediol had little effect on the size of the DMPC liposomes or the surface pressure (π)-surface area (A) isotherm of DMPC monolayers at an air-water interface, whereas 1,2,3-propanetriol or 1,2,3,4-butanetetraol increased both liposome size and surface pressure. Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) and differential scanning calorimetry (DSC) were used to evaluate the interaction between DMPC and polyols. These experimental results suggest that the chemical structure of polyol plays an important role in the characteristic interaction between polyol and DMPC.

Does tranexamic acid alter the risk of thromboembolism after total hip arthroplasty in the absence of routine chemical thromboprophylaxis?

Tranexamic acid (TXA) has been used to reduce blood loss during total hip arthroplasty (THA), but its use could increase the risk of venous thromboembolic disease (VTE). Several studies have reported that TXA does not increase the prevalence of deep vein thrombosis (DVT), but most of those used routine chemical thromboprophylaxis, thereby masking the potential increased risk of TXA on VTE. We wished to ascertain whether TXA increases the prevalence of VTE in patients undergoing THA without routine chemical thromboprophylaxis. We carried out a retrospective case-control study in 254 patients who underwent a primary THA, 127 of whom received TXA (1 g given pre-operatively) and a control group of 127 who did not. All patients had mechanical but no chemical thomboprophylaxis. Each patient was examined for DVT by bilateral ultrasonography pre-operatively and on post-operative days 1 and 7. TXA was found to statistically significantly increase the incidence of total DVT on post-operative day 7 compared with the control group (24 (18.9%) and 12 (9.4%), respectively; p < 0.05) but most cases of DVT were isolated distal DVT, with the exception of one patient with proximal DVT in each group. One patient in the control group developed a non-fatal symptomatic pulmonary embolism (PE). The use of TXA did not appear to affect the prevalence of either proximal DVT or PE.

Cite this article: Bone Joint J 2015; 97-B:458–62.