Synthesis of 2D Germanane (GeH): a New,Fast, and Facile Approach

Germanane (GeH), a germanium analogue of graphane, has recently attracted considerable interest because its remarkable combination of properties makes it an extremely suitable candidate to be used as 2D material for field effect devices, photovoltaics, and photocatalysis. Up to now, the synthesis of GeH has been conducted by substituting Ca by H in a β‐CaGe₂ layered Zintl phase through topochemical deintercalation in aqueous HCl. This reaction is generally slow and takes place over 6 to 14 days. The new and facile protocol presented here allows to synthesize GeH at room temperature in a significantly shorter time (a few minutes), which renders this method highly attractive for technological applications. The GeH produced with this method is highly pure and has a band gap (E_g) close to 1.4 eV, a lower value than that reported for germanane synthesized using HCl, which is promising for incorporation of GeH in solar cells.     

Synthesis of 2D Germanane (GeH): a New,Fast, and Facile Approach

Germanane (GeH), a germanium analogue of graphane, has recently attracted considerable interest because its remarkable combination of properties makes it an extremely suitable candidate to be used as 2D material for field effect devices, photovoltaics, and photocatalysis. Up to now, the synthesis of GeH has been conducted by substituting Ca by H in a β‐CaGe₂ layered Zintl phase through topochemical deintercalation in aqueous HCl. This reaction is generally slow and takes place over 6 to 14 days. The new and facile protocol presented here allows to synthesize GeH at room temperature in a significantly shorter time (a few minutes), which renders this method highly attractive for technological applications. The GeH produced with this method is highly pure and has a band gap (E_g) close to 1.4 eV, a lower value than that reported for germanane synthesized using HCl, which is promising for incorporation of GeH in solar cells.     

Hydrogenated Graphene and Hydrogenated Silicene: Computational Insights

Density functional calculations are performed to study the energetic, structural, and electronic properties of graphene and silicene functionalized with hydrogen. Our calculations predict that H atoms bind much more strongly to silicene than to graphene. The adsorbed H atoms tend to cooperatively stabilize each other leading to a two‐dimensional nucleation and growth mechanism. The different structural and electronic modifications induced by H in fully functionalized graphene and silicene (known as graphane and silicane) are also explained. Finally, the electronic properties of defective graphane with multiple hydrogen vacancies are investigated. Engineering the vacancies in graphane offers a way to modify the electronic properties of this material.     

Alkali Metal Arenides as a Universal Synthetic Tool for Layered 2D Germanene Modification

The rediscovery of graphene in 2004 has started an enormous chase in the research of 2D materials. A new family of layered 2D materials consisting of the 14th group elements beyond carbon has already been reported. Here, a new methodology in germanene chemistry is presented using germanane (Ge₆H₆) as a stable and easily accessible starting material for effective synthesis of novel germanene derivatives. The modification procedure utilizing strong bases—alkali metal arenides—for deprotonation of germanane and its subsequent functionalization with p‐nitrobenzyl bromide is described. Functionalization of germanene is confirmed by FT‐IR, Raman, and XPS spectroscopy as well as by X‐ray diffraction analysis.     

Polymorphic phase transformations of 3‐chloro‐trans‐cinnamic acid and its solid solution with 3‐bromo‐trans‐cinnamic acid

We have investigated the polymorphic phase transformations above ambient temperature for 3‐chloro‐trans‐cinnamic acid (3‐ClCA, C₉H₇ClO₂) and a solid solution of 3‐ClCA and 3‐bromo‐trans‐cinnamic acid (3‐BrCA, C₉H₇BrO₂). At 413 K, the γ polymorph of 3‐ClCA transforms to the β polymorph. Interestingly, the structure of the β polymorph of 3‐ClCA obtained in this transformation is different from the structure of the β polymorph of 3‐BrCA obtained in the corresponding polymorphic transformation from the γ polymorph of 3‐BrCA, even though the γ polymorphs of 3‐ClCA and 3‐BrCA are isostructural. We also report a high‐temperature phase transformation from a γ‐type structure to a β‐type structure for a solid solution of 3‐ClCA and 3‐BrCA (with a molar ratio close to 1:1). The γ polymorph of the solid solution is isostructural with the γ polymorphs of pure 3‐ClCA and pure 3‐BrCA, while the β‐type structure produced in the phase transformation is structurally similar to the β polymorph of pure 3‐BrCA.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

Transparent,Ultrahigh‐Gas‐Barrier Films with a Brick–Mortar–Sand Structure

Transparent and flexible gas‐barrier materials have shown broad applications in electronics, food, and pharmaceutical preservation. Herein, we report ultrahigh‐gas‐barrier films with a brick–mortar–sand structure fabricated by layer‐by‐layer (LBL) assembly of XAl‐layered double hydroxide (LDH, X=Mg, Ni, Zn, Co) nanoplatelets and polyacrylic acid (PAA) followed by CO₂ infilling, denoted as (XAl‐LDH/PAA)_n‐CO₂. The near‐perfectly parallel orientation of the LDH “brick” creates a long diffusion length to hinder the transmission of gas molecules in the PAA “mortar”. Most significantly, both the experimental studies and theoretical simulations reveal that the chemically adsorbed CO₂ acts like “sand” to fill the free volume at the organic–inorganic interface, which further depresses the diffusion of permeating gas. The strategy presented here provides a new insight into the perception of barrier mechanism, and the (XAl‐LDH/PAA)_n‐CO₂ film is among the best gas barrier films ever reported.     

Transparent,Ultrahigh‐Gas‐Barrier Films with a Brick–Mortar–Sand Structure

Transparent and flexible gas‐barrier materials have shown broad applications in electronics, food, and pharmaceutical preservation. Herein, we report ultrahigh‐gas‐barrier films with a brick–mortar–sand structure fabricated by layer‐by‐layer (LBL) assembly of XAl‐layered double hydroxide (LDH, X=Mg, Ni, Zn, Co) nanoplatelets and polyacrylic acid (PAA) followed by CO₂ infilling, denoted as (XAl‐LDH/PAA)_n‐CO₂. The near‐perfectly parallel orientation of the LDH “brick” creates a long diffusion length to hinder the transmission of gas molecules in the PAA “mortar”. Most significantly, both the experimental studies and theoretical simulations reveal that the chemically adsorbed CO₂ acts like “sand” to fill the free volume at the organic–inorganic interface, which further depresses the diffusion of permeating gas. The strategy presented here provides a new insight into the perception of barrier mechanism, and the (XAl‐LDH/PAA)_n‐CO₂ film is among the best gas barrier films ever reported.     

Van Der Waals heterogeneous layer‐layer carbon nanostructures involving π···H‐C‐C‐H···π···H‐C‐C‐H stacking based on graphene and graphane sheets

Noncovalent interactions involving aromatic rings, such as π···π stacking, CH···π are very essential for supramolecular carbon nanostructures. Graphite is a typical homogenous carbon matter based on π···π stacking of graphene sheets. Even in systems not involving aromatic groups, the stability of diamondoid dimer and layer‐layer graphane dimer originates from C − H···H − C noncovalent interaction. In this article, the structures and properties of novel heterogeneous layer‐layer carbon‐nanostructures involving π···H‐C‐C‐H···π···H‐C‐C‐H stacking based on [n ]‐graphane and [n ]‐graphene and their derivatives are theoretically investigated for n = 16–54 using dispersion corrected density functional theory B3LYP‐D3 method. Energy decomposition analysis shows that dispersion interaction is the most important for the stabilization of both double‐ and multi‐layer‐layer [n ]‐graphane@graphene. Binding energy between graphane and graphene sheets shows that there is a distinct additive nature of CH···π interaction. For comparison and simplicity, the concept of H‐H bond energy equivalent number of carbon atoms (noted as NHEQ), is used to describe the strength of these noncovalent interactions. The NHEQ of the graphene dimers, graphane dimers, and double‐layered graphane@graphene are 103, 143, and 110, indicating that the strength of C‐H···π interaction is close to that of π···π and much stronger than that of C‐H···H‐C in large size systems. Additionally, frontier molecular orbital, electron density difference and visualized noncovalent interaction regions are discussed for deeply understanding the nature of the C‐H···π stacking interaction in construction of heterogeneous layer‐layer graphane@graphene structures. We hope that the present study would be helpful for creations of new functional supramolecular materials based on graphane and graphene carbon nano‐structures. © 2017 Wiley Periodicals, Inc.     

Barrierless Single‐Electron‐Induced cis–trans Isomerization

Lowering the activation energy of a chemical reaction is an essential part in controlling chemical reactions. By attaching a single electron, a barrierless path for the cis–trans isomerization of maleonitrile on the anionic surface is formed. The anionic activation can be applied in both reaction directions, yielding the desired isomer. We identify the microscopic mechanism that leads to the formation of the barrierless route for the electron‐induced isomerization. The generalization to other chemical reactions is discussed.     

Alternative Synthesis and Structures of C‐monoacetylenic Phosphaalkenes

An alternative synthesis of C‐monoacetylenic phosphaalkenes trans‐Mes*P=C(Me)(C≡CR) (Mes* = 2, 4, 6‐^tBu₃Ph, R = Ph, SiMe₃) from C‐bromophosphaalkenes cis‐Mes*P=C(Me)Br using standard Sonogashira coupling conditions is described. Crystallographic studies confirm cis‐trans isomerization of the P=C double bond during Pd‐catalyzed cross coupling, leading exclusively to trans‐acetylenic phosphaalkenes. Crystallographic studies of all synthesized compounds reveal the extend of π‐conjugation over the acetylene and P=C π‐systems.     

From Sponges to Nanotubes: A Change of Nanocrystal Morphology for Acute‐Angle Bent‐Core Molecules

The crystalline (B₄) phase made of acute‐angle bent‐core molecules (1,7‐naphthalene derivatives), which exhibits an unusual, highly porous sponge‐like morphology, is presented. However, if grown in the presence of low‐weight mesogenic molecules, the same crystal forms nanotubes with a very high aspect ratio. The nanotubes become unstable upon increasing the amount of dopant molecules, and the sponge‐like morphology reappears. The phase is optically active, and the optical activity is an order of magnitude smaller than in the B₄ phase made of conventional bent‐core molecules. The optical activity is related to the spatial inhomogeneity of the layered structure and is reduced due to the low apex angle and low tilt of the molecules. The arrangement of molecules within the layers was deduced from the bathochromic absorption shift in the B₄ phase.     

A New Two‐dimensional Cyano‐bridged Chromium (HI)‐Nickel (II) Bimetallic Assembly with Stair‐like Layers

From the reaction of K₃[Cr(CN)₆] and [NiL](CIO₄)₂ (L= 1,8‐di(hydroxyethyl)‐l, 3, 6, 8, 10, 13‐hexaazacyclotetradecane), an infinite stair‐like layered assembly [NiL]₃ [Cr‐(CN)₆]₂‐6.5H₂O is obtained, in which each hexacyanochromate(III) ion connects three nickel(II) ions using three cis Of groups and the bridging cyanide ligands coordinate to the nickel ion in a trans fashion forming trans‐NiL(N°C)₂ moieties.     

A Natural Glycyrrhizic Acid‐Tailored Light‐Responsive Gelator

The construction of stimuli‐responsive materials by using naturally occurring molecules as building blocks has received increasing attention owing to their bioavailability, biocompatibility, and biodegradability. Herein, a symmetrical azobenzene‐functionalized natural glycyrrhizic acid (trans‐ GAG ) was synthesized and could form stable supramolecular gels in DMSO/H₂O and MeOH/H₂O. Owing to trans–cis isomerization, this gel exhibited typical light‐responsive behavior that led to a reversible gel–sol transition accompanied by a variation in morphology and rheology. Additionally, this trans‐ GAG gel displayed a distinct injectable self‐healing property and outstanding biocompatibility. This work provides a simple yet rational strategy to fabricate stimuli‐responsive materials from naturally occurring, eco‐friendly molecules.     

The Reaction of 2‐X‐1, 2‐Difluoroalk‐1‐enyldifluoroboranes with Xenon Difluoride. A Methodical Approach to 1, 2‐Difluoroalk‐1‐enylxenon(II) Salts

2‐X‐1, 2‐Difluoroalk‐1‐enylxenon(II) salts were prepared by the reaction of XeF₂ with XCF=CFBF₂ (X = F, trans‐H, cis‐Cl, trans‐Cl, cis‐CF₃, cis‐C₂F₅) but no organoxenon(II) compounds were obtained when the trans‐isomers of boranes, trans‐XCF=CFBF₂ (X = CF₃, C₄F₉, C₄H₉, Et₃Si), were used under similar conditions.     

Designed Synthesis of a 1D Polymer in Twist‐Stacked Topology via Single‐Crystal‐to‐Single‐Crystal Polymerization

To synthesize a fully organic 1D polymer in a novel twist‐stacked topology, we designed a peptide monomer HC≡CCH₂‐NH‐Ile‐Leu‐N₃, which crystallizes with its molecules H‐bonded along a six‐fold screw axis. These H‐bonded columns pack parallelly such that molecules arrange head‐to‐tail, forming linear non‐covalent chains in planes perpendicular to the screw axis. The chains arrange parallelly to form molecular layers which twist‐stack along the screw axis. Crystals of this monomer, on heating, undergo single‐crystal‐to‐single‐crystal (SCSC) topochemical azide–alkyne cycloaddition (TAAC) polymerization to yield an exclusively 1,4‐triazole‐linked polymer in a twist‐stacked layered topology. This topologically defined polymer shows better mechanical strength and thermal stability than its unordered form, as evidenced by nanoindentation studies and thermogravimetric analysis, respectively. This work illustrates the scope of topochemical polymerizations for synthesizing polymers in pre‐decided topologies.     

Uranium–Carbene–Imido Metalla‐Allenes: Ancillary‐Ligand‐Controlled cis‐/trans‐Isomerisation and Assessment of trans Influence in the R2C=UIV=NR′ Unit (R=Ph2PNSiMe3; R′=CPh3)

Uranium(IV)–carbene–imido complexes [U(BIPM^TMS)(NCPh₃)(κ²‐N,N′‐BIPY)] ( 2 ; BIPM^TMS=C(PPh₂NSiMe₃)₂; BIPY=2,2‐bipyridine) and [U(BIPM^TMS)(NCPh₃)(DMAP)₂] ( 3 ; DMAP=4‐dimethylamino‐pyridine) that contain unprecedented, discrete R₂C=U=NR′ units are reported. These complexes complete the family of E=U=E (E=CR₂, NR, O) metalla‐allenes with feasible first‐row hetero‐element combinations. Intriguingly, 2 and 3 contain cis‐ and trans‐C=U=N units, respectively, representing rare examples of controllable cis/trans isomerisation in f‐block chemistry. This work reveals a clear‐cut example of the trans influence in a mid‐valent uranium system, and thus a strong preference for the cis isomer, which is computed in a co‐ligand‐free truncated model—to isolate the electronic trans influence from steric contributions—to be more stable than the trans isomer by approximately 12 kJ mol^?1 with an isomerisation barrier of approximately 14 kJ mol^?1.     

Synthesis of trans‐Disubstituted Alkenes by Cobalt‐Catalyzed Reductive Coupling of Terminal Alkynes with Activated Alkenes

A cobalt‐catalyzed reductive coupling of terminal alkynes, RC?CH, with activated alkenes, R′CH?CH₂, in the presence of zinc and water to give functionalized trans‐disubstituted alkenes, RCH?CHCH₂CH₂R′, is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl₂/P(OMe)₃/Zn catalyst system to afford 1,2‐trans‐disubstituted alkenes with high regio‐ and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl₂/P(OPh)₃/Zn system providing a mixture of 1,2‐trans‐ and 1,1‐disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3‐enynes and acetylene gas with alkenes. Furthermore, a phosphine‐free cobalt‐catalyzed reductive coupling of terminal alkynes with enones, affording 1,2‐trans‐disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air‐stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.     

Bis[(μ‐cyclopentylamino‐N:N)dimethyl­aluminium(III)]

Reaction of AlMe₃ with NH₂(C₅H₉) caused the evolution of methane and produced the dimeric species bis(μ‐cyclo­pentyl­amino‐N:N)bis[dimethylaluminium(III)], [Al(CH₃)₂‐(C₅H₁₀N)]₂, which was found to adopt a cis configuration of cyclopentyl groups about a bent AlNAlN ring (which has twofold crystallographic symmetry) instead of the more common trans arrangement.