Unusual Redox Chemistry of Ytterbium Carbazole–Bis(oxazoline) Compounds: Oxidative Coupling of Primary Phosphines by an Ytterbium Carbazole–Bis(oxazoline) Dialkyl

The 1,8-bis­(4′,4′-dimethyloxazolin-2′-yl)-3,6-di-<i>tert</i>-butylcarbazole anion (Czx) forms monomeric, six-coordinate halide complexes of Yb­(II), (Czx)­Yb­(X)­(THF)₂ (X = I (<b>2</b>), Cl (<b>3</b>)), by metathesis of YbX₂ with NaCzx (<b>1</b>) or Na/Hg reduction of (Czx)­Yb­(Cl)₂(THF). The crystal structure of <b>1</b> reveals a polymeric chain structure in which the oxazoline ring bridges to the Na⁺ of an adjacent unit. The iodo complex <b>2</b> serves as a precursor to divalent silylamide, alkyl, and phosphide complexes, (Czx)­Yb­(X)­(THF)_<i>n</i> (<b>4</b>, X = N­(SiMe₃)₂, <i>n</i> = 1; <b>5</b>, X = CH­(SiMe₃)₂, <i>n</i> = 1; <b>7a</b>, X = 2,4,6-Me₃C₆H₂PH, <i>n</i> = 2; <b>7b</b>, X = 2,4,6-Prⁱ₃C₆H₂PH, <i>n</i> = 2). The X-ray structure of <b>4</b> reveals a distorted-trigonal-bipyramidal geometry with the Czx ligand occupying two axial sites and one equatorial site in a pseudo-<i>mer</i> coordination mode. In contrast to the typical metathesis chemistry observed with LiCH­(SiMe₃)₂, an unusual <i>oxidation</i> occurs when <b>2</b> or <b>3</b> is treated with LiCH₂SiMe₃ to generate the previously isolated trivalent alkyl (Czx)­Yb­(CH₂SiMe₃)₂. Trivalent Yb complexes with the Czx ligand also display unusual redox chemistry: rapid <i>reduction</i> to the Yb­(II) phosphides <b>7a</b>,<b>b</b> is observed on treatment of <i>mer,cis</i>-(Czx)­Yb­(Cl)₂(THF) with ArPH^– Na⁺ (<b>6a</b>,<b>b</b>) or, equivalently, on treatment of (Czx)­Yb­(CH₂SiMe₃)₂ with ArPH₂. In both cases, oxidative coupling of the phosphide or phosphine was observed to form <i>meso</i>- and <i>rac</i>-biphosphines, ArPH–PHAr (Ar = 2,4,6-Me₃C₆H₂ (<b>9a</b>), 2,4,6-Prⁱ₃C₆H₂ (<b>9b</b>))

Unusual Redox Chemistry of Ytterbium Carbazole–Bis(oxazoline) Compounds: Oxidative Coupling of Primary Phosphines by an Ytterbium Carbazole–Bis(oxazoline) Dialkyl

The 1,8-bis­(4′,4′-dimethyloxazolin-2′-yl)-3,6-di-<i>tert</i>-butylcarbazole anion (Czx) forms monomeric, six-coordinate halide complexes of Yb­(II), (Czx)­Yb­(X)­(THF)₂ (X = I (<b>2</b>), Cl (<b>3</b>)), by metathesis of YbX₂ with NaCzx (<b>1</b>) or Na/Hg reduction of (Czx)­Yb­(Cl)₂(THF). The crystal structure of <b>1</b> reveals a polymeric chain structure in which the oxazoline ring bridges to the Na⁺ of an adjacent unit. The iodo complex <b>2</b> serves as a precursor to divalent silylamide, alkyl, and phosphide complexes, (Czx)­Yb­(X)­(THF)_<i>n</i> (<b>4</b>, X = N­(SiMe₃)₂, <i>n</i> = 1; <b>5</b>, X = CH­(SiMe₃)₂, <i>n</i> = 1; <b>7a</b>, X = 2,4,6-Me₃C₆H₂PH, <i>n</i> = 2; <b>7b</b>, X = 2,4,6-Prⁱ₃C₆H₂PH, <i>n</i> = 2). The X-ray structure of <b>4</b> reveals a distorted-trigonal-bipyramidal geometry with the Czx ligand occupying two axial sites and one equatorial site in a pseudo-<i>mer</i> coordination mode. In contrast to the typical metathesis chemistry observed with LiCH­(SiMe₃)₂, an unusual <i>oxidation</i> occurs when <b>2</b> or <b>3</b> is treated with LiCH₂SiMe₃ to generate the previously isolated trivalent alkyl (Czx)­Yb­(CH₂SiMe₃)₂. Trivalent Yb complexes with the Czx ligand also display unusual redox chemistry: rapid <i>reduction</i> to the Yb­(II) phosphides <b>7a</b>,<b>b</b> is observed on treatment of <i>mer,cis</i>-(Czx)­Yb­(Cl)₂(THF) with ArPH^– Na⁺ (<b>6a</b>,<b>b</b>) or, equivalently, on treatment of (Czx)­Yb­(CH₂SiMe₃)₂ with ArPH₂. In both cases, oxidative coupling of the phosphide or phosphine was observed to form <i>meso</i>- and <i>rac</i>-biphosphines, ArPH–PHAr (Ar = 2,4,6-Me₃C₆H₂ (<b>9a</b>), 2,4,6-Prⁱ₃C₆H₂ (<b>9b</b>))

An Integrated Amplification-Free Digital CRISPR/Cas-Assisted Assay for Single Molecule Detection of RNA

Conventional nucleic acid detection technologies usually rely on amplification to improve sensitivity, which has drawbacks, such as amplification bias, complicated operation, high requirements for complex instruments, and aerosol pollution. To address these concerns, we developed an integrated assay for the enrichment and single molecule digital detection of nucleic acid based on a CRISPR/Cas13a and microwell array. In our design, magnetic beads capture and concentrate the target from a large volume of sample, which is 100 times larger than reported earlier. The target-induced CRISPR/Cas13a cutting reaction was then dispersed and limited to a million individual femtoliter-sized microwells, thereby enhancing the local signal intensity to achieve single-molecule detection. The limit of this assay for amplification-free detection of SARS-CoV-2 is 2 aM. The implementation of this study will establish a “sample-in-answer-out” single-RNA detection technology without amplification and improve the sensitivity and specificity while shortening the detection time. This research has broad prospects in clinical application

Anisotropic Electrical Properties from Vapor–Solid–Solid Grown Bi₂Se₃ Nanoribbons and Nanowires

High-quality Bi₂Se₃ nanoribbons and nanowires were synthesized by a Au-catalyzed chemical vapor deposition method. Detailed structural and chemical characterizations using scanning and transmission electron microscopy show that the growth of both Bi₂Se₃ nanoribbons and nanowires is governed by the vapor–solid–solid growth mechanism, and the nanoribbons grow along ⟨112̅0⟩ and nanowires grow along ⟨0001⟩ directions. Detailed <i>in situ</i> scanning tunneling microscope–transmission electron microscopy electrical measurements show that the nanoribbons are much more conductive than the nanowires with a conductivity anisotropy ratio of ∼2.5 × 10² at room temperature

Highly Ordered Cubic Mesoporous Materials with the Same Symmetry but Tunable Pore Structures

In this article, two highly ordered mesoporous silica materials with the same face-centered cubic (<i>fcc</i>) symmetry but distinctly different pore structures have been synthesized by simply changing the amount of silica source. Their structures have been extensively studied by Synchrotron small-angle X-ray scattering, N₂ sorption analysis, scanning and transmission electron microscopy observations, and electron tomography. One mesoporous material formed by a hard sphere packing (HSP) pathway exhibits a bimodal pore distribution, while the other has a conventional FDU-12-type mesostructure with a single-sized pore. By increasing the amount of the silica source, the cavities formed by the packing of composite spherical micelles in the HSP mesostructure are gradually filled by the excess of siliceous species, leading to the conventional FDU-12-type mesostructure with the disappearance of bimodal pores. The pore connectivity of the HSP mesoporous material hydrothermally treated at 150 °C has been further investigated. Taking advantage of the ultrathin tomographic slices, the sizes of cage, cavity, and connectivity are measured to be 14.5, 10.5, and 6.4 nm, respectively. More importantly, the pore connection between the cage and cavity is directly observed to occur along the ⟨100⟩ direction, different from the FDU-12-type mesostructure in which the connection appears between two adjacent cages along the ⟨110⟩ direction. This work represents an unusual example where two ordered cage-type mesoporous materials with the same symmetry can be synthesized by slightly changing the synthesis condition, but their pore structures and pore connections are significantly different. Our finding is important for understanding the formation mechanism and for the rational design and controllable synthesis of novel mesoporous materials

Highly Ordered Cubic Mesoporous Materials with the Same Symmetry but Tunable Pore Structures

In this article, two highly ordered mesoporous silica materials with the same face-centered cubic (<i>fcc</i>) symmetry but distinctly different pore structures have been synthesized by simply changing the amount of silica source. Their structures have been extensively studied by Synchrotron small-angle X-ray scattering, N₂ sorption analysis, scanning and transmission electron microscopy observations, and electron tomography. One mesoporous material formed by a hard sphere packing (HSP) pathway exhibits a bimodal pore distribution, while the other has a conventional FDU-12-type mesostructure with a single-sized pore. By increasing the amount of the silica source, the cavities formed by the packing of composite spherical micelles in the HSP mesostructure are gradually filled by the excess of siliceous species, leading to the conventional FDU-12-type mesostructure with the disappearance of bimodal pores. The pore connectivity of the HSP mesoporous material hydrothermally treated at 150 °C has been further investigated. Taking advantage of the ultrathin tomographic slices, the sizes of cage, cavity, and connectivity are measured to be 14.5, 10.5, and 6.4 nm, respectively. More importantly, the pore connection between the cage and cavity is directly observed to occur along the ⟨100⟩ direction, different from the FDU-12-type mesostructure in which the connection appears between two adjacent cages along the ⟨110⟩ direction. This work represents an unusual example where two ordered cage-type mesoporous materials with the same symmetry can be synthesized by slightly changing the synthesis condition, but their pore structures and pore connections are significantly different. Our finding is important for understanding the formation mechanism and for the rational design and controllable synthesis of novel mesoporous materials

Immagini d'acqua nelle poesie d'amore del Kokinwakashu

Influenced by the Buddhist view of human life as transient, and by the Buddhist distrust of love, the compilers of the Kokinwakashū in the five books of love poems structured the development of an imaginary romance according to a pattern of blossoming, flourishing and decline. It is interesting to note that the different stages of this romance are described from beginning to end through impressive images of water. A mountain torrent running swiftly suggests the intense agitation of feelings caused by love. Waterfalls and waves are very effective to express people’s rising rumors about a love affair, whereas rivers and sometimes oceans offer an obvious metaphor for lover’s tears of grief and tears of longing. In some cases, an heartless woman who refuses her suitor is described as a desolate bay, while an abandoned lover feels like vanishing bubbles on running water. According to the first imperial anthology, love is a force of nature whose power is great enough to destroy man but it is also an impermanent and unreliable thing like a mountain torrent which continuously brings wherever it wants its agitated water

Scalable Growth of High Mobility Dirac Semimetal Cd₃As₂ Microbelts

Three-dimensional (3D) Dirac semimetals are 3D analogues of graphene, which display Dirac points with linear dispersion in <i>k</i>-space, stabilized by crystal symmetry. Cd₃As₂ has been predicted to be 3D Dirac semimetals and was subsequently demonstrated by angle-resolved photoemission spectroscopy. As unveiled by transport measurements, several exotic phases, such as Weyl semimetals, topological insulators, and topological superconductors, can be deduced by breaking time reversal or inversion symmetry. Here, we reported a facile and scalable chemical vapor deposition method to fabricate high-quality Dirac semimetal Cd₃As₂ microbelts; they have shown ultrahigh mobility up to 1.15 × 10⁵ cm² V⁻¹ s⁻¹ and pronounced Shubnikov–de Haas oscillations. Such extraordinary features are attributed to the suppression of electron backscattering. This research opens a new avenue for the scalable fabrication of Cd₃As₂ materials toward exciting electronic applications of 3D Dirac semimetals

Rational Design of Bi₂Te₃ Polycrystalline Whiskers for Thermoelectric Applications

Bi₂Te₃ polycrystalline whiskers consisting of interconnected nanoplates have been synthesized through chemical transformation from In₂Te₃ polycrystalline whisker templates assembled by nanoparticles. The synthesized Bi₂Te₃ whiskers preserve the original one-dimensional morphology of the In₂Te₃, while the In₂Te₃ nanoparticles can be transformed into the Bi₂Te₃ thin nanoplates, accompanied by the formation of high-density interfaces between nanoplates. The hot-pressed nanostructures consolidated from Bi₂Te₃ polycrystalline whiskers at 400 °C demonstrate a promising figure of merit (<i>ZT</i>) of 0.71 at 400 K, which can be attributed to their low thermal conductivity and relatively high electrical conductivity. The small nanoparticles inherited from the polycrystalline whiskers and high-density nanoparticle interfaces in the hot-pressed nanostructures contribute to the significant reduction of thermal conductivity. This study provides a rational chemical transformation approach to design and synthesize polycrystalline microstructures for enhanced thermoelectric performances

Planar Vacancies in Sn_1–<i>x</i>Bi_<i>x</i>Te Nanoribbons

Vacancy engineering is a crucial approach to manipulate physical properties of semiconductors. Here, we demonstrate that planar vacancies are formed in Sn_1–<i>x</i>Bi_<i>x</i>Te nanoribbons by using Bi dopants <i>via</i> a facile chemical vapor deposition. Through combination of sub-angstrom-resolution imaging and density functional theory calculations, these planar vacancies are found to be associated with Bi segregations, which significantly lower their formation energies. The planar vacancies exhibit polymorphic structures with local variations in the lattice relaxation level, determined by their proximity to the nanoribbon surface. Such polymorphic planar vacancies, in conjunction with Bi dopants, trigger distinct localized electronic states, offering platforms for device applications of ternary chalcogenide materials