Synthesis,crystal structure,and physical properties of a new boride Ga2Ni21B20 with a modified Zn2Ni21B20-type structure

A ternary boride Ga₂Ni₂₁B₂₀, with modified Zn₂Ni₂₁B₂₀-type structure (space group I4/mmm, and lattice parameters a = 7.2164(1) Å, c = 14.2715(4) Å), was synthesized from the constituent elements. Single crystal diffraction data reveal Ni at 8f site splitting into 16m position with nearly half occupancy. In this structure, [Ni₆B₂₀] cages share ligand boron atoms with [Ga₂B₄Ni₉] hexa-capped square prisms, forming two dimensional layers. Layers are interconnected via Ga−Ni interactions and build up a three-dimensional framework. Quasi-two-dimensional infinite planar nets formed by intercrossed Ni atoms are embedded. Ga₂Ni₂₁B₂₀ is a metallic Pauli paramagnet, in agreement with electronic structure calculations, resulting in 8.2 states eV⁻¹ f.u⁻¹ at the Fermi level.     

Desymmetrization of an Octahedral Coordination Complex Inside a Self‐Assembled Exoskeleton

The synthesis of a centrally functionalized, ribbon‐shaped [6]polynorbornane ligand L that self‐assembles with Pd^II cations into a {Pd₂ L ₄} coordination cage is reported. The shape‐persistent {Pd₂ L ₄} cage contains two axial cationic centers and an array of four equatorial H‐bond donors pointing directly towards the center of the cavity. This precisely defined supramolecular environment is complementary to the geometry of classic octahedral complexes [M(XY)₆] with six diatomic ligands. Very strong binding of [Pt(CN)₆]^2? to the cage was observed, with the structure of the host–guest complex {[Pt(CN)₆]@Pd₂L₄} supported by NMR spectroscopy, MS, and X‐ray data. The self‐assembled shell imprints its geometry on the encapsulated guest, and desymmetrization of the octahedral platinum species by the influence of the D_4h‐symmetric second coordination sphere was evidenced by IR spectroscopy. [Fe(CN)₆]^3? and square‐planar [Pt(CN)₄]^2? were strongly bound. Smaller octahedral anions such as [SiF₆]^2?, neutral carbonyl complexes ([M(CO)₆]; M=Cr, Mo, W) and the linear [Ag(CN)₂]^? anion were only weakly bound, showing that both size and charge match are key factors for high‐affinity binding.     

Use of anions to allow translational isomerism of a [2]rotaxane

We report a molecular [2]rotaxane which comprises a molecular cage and a dumbbell-shaped component, in which translational isomerism can be performed reversibly through an in situ anion exchange process, that is, sequential addition of Bu4NCl/AgPF6 reagent pairs. The [2]rotaxane incorporates two pyridinium and two dialkylammonium centers and functions as a triply operable molecular switch, which can be controlled through altering the polarity of the solvent, adding acidic and basic reagents (TFA/Et3N), and the varying the nature of the counteranions (Cl- vs PF6-).     

Star PolyMOCs with Diverse Structures,Dynamics, and Functions by Three‐Component Assembly

We report star polymer metal–organic cage (polyMOC) materials whose structures, mechanical properties, functionalities, and dynamics can all be precisely tailored through a simple three‐component assembly strategy. The star polyMOC network is composed of tetra‐arm star polymers functionalized with ligands on the chain ends, small molecule ligands, and palladium ions; polyMOCs are formed via metal–ligand coordination and thermal annealing. The ratio of small molecule ligands to polymer‐bound ligands determines the connectivity of the MOC junctions and the network structure. The use of large M₁₂L₂₄ MOCs enables great flexibility in tuning this ratio, which provides access to a rich spectrum of material properties including tunable moduli and relaxation dynamics.     

A Covalent Organic Helical Cage with Remarkable Chiroptical Amplification

Purely organic shape‐persistent chiral cages are designed through the use of rigid chiral axes. Covalent dimerization of a tripodal fragment bearing chiral allenes forms a molecular twisted prism with loop‐like lateral edges presenting 10‐fold chiroptical amplification compared to its isolated building blocks. The expected geometry of covalent organic helical cage (M,M)₃‐ 1 was confirmed by X‐ray crystal structure analysis. Comparison of the chiroptical responses of this shape‐persistent molecular container with more flexible analogues highlights how the control of the conformational freedom of the molecule can be used to obtain molecular cages with strong chiroptical responses. Selective inclusion‐complex formation with ferrocenium ions [(P,P)₃‐ 1 @Fc⁺] was confirmed and quantified with HR‐ESI‐MS and NMR spectroscopy.     

Encapsulation of Halocarbons in a Tetrahedral Anion Cage

Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilization. Well‐studied examples are mainly metal‐coordination‐based or covalent architectures. An anion‐coordination‐based cage that is capable of encapsulating halocarbon guests is reported for the first time. This A₄L₄‐type (A=anion) tetrahedral cage, [(PO₄)₄ L ₄]^12?, assembled from a C₃‐symmetric tris(bisurea) ligand ( L ) and phosphate ion (PO₄^3?), readily accommodates a series of quasi‐tetrahedral halocarbons, such as the Freon components CFCl₃, CF₂Cl₂, CHFCl₂, and C(CH₃)F₃, and chlorocarbons CH₂Cl₂, CHCl₃, CCl₄, C(CH₃)Cl₃, C(CH₃)₂Cl₂, and C(CH₃)₃Cl. The guest encapsulation in the solid state is confirmed by crystal structures, while the host–guest interactions in solution were demonstrated by NMR techniques.     

Oxidation behavior with quantum dots formation from amorphous GaAs thin films

ABSTRACT

We investigated the oxidation behaviour of an amorphous GaAs thin film deposited onto a micro/nanotextured Si surface by an electron beam. After the deposited film was exposed to air, microcrystallites were formed with octahedral cubic and monoclinic structures of arsenic oxides. Short time exposure after thin film deposition showed the formation of cubic arsenolite while long time exposure showed the formation of monoclinic claudetites as well as cubic arsenolites. These oxide microcrystallites at the GaAs thin film surface disappeared after the sample annealing process. However, the amorphous GaAs thin film included high-density GaAs nanodots. From UV and inverse photoemission spectroscopies, the thin film showed n-type band structure with an energy gap of 2.73?eV. Photoluminescence measurement showed an emission peak at (450–513)?nm with the energy of (2.41–2.75)?eV corresponding to dot size of (4.1–4.5)?nm.