Inorganic Solid-State Nonlinear Optical Switch with a Linearly Tunable Tc Spanning a Wide Temperature Range

Nonlinear optical (NLO) switch materials that turn on/off second-harmonic generation (SHG) at a phase transition temperature (T_c) are promising for applications in the fields of photoswitching and optical computing. However, precise control of T_c remains challenging, mainly because a linearly tunable T_c has not been reported to date. Herein, we report a unique selenate, tetragonal P 2₁c [Ag(NH₃)₂]₂SeO₄ with a=b=8.5569(2) Å and c=6.5208(2) Å that exhibits a strong SHG intensity (1.3×KDP) and a large birefringence (Δn_obv.=0.08). This compound forms a series of isostructural solid-solution crystals [Ag(NH₃)₂]₂S_xSe_1−xO₄ (x=0–1.00) that exhibit excellent NLO switching performance and an unprecedented linearly tunable spanning 430 to 356 K. The breaking of localized hydrogen bonds between SeO₄²⁻ and the cation triggers a phase transition accompanied by hydrogen bond length changes with increasing x and a linear change in the enthalpy .     

Synthesis,Structure and Nickel Carbonyl Complexes of Dialkylterphenyl Phosphines

The experimental and computational characterization of a series of dialkylterphenyl phosphines, PR₂Ar′ is described. The new P-donors comprise five compounds of general formula PR₂Ar (R=Me, Et, iPr, c-C₅H₉ and c-C₆H₁₁); Ar = 2,6-C₆H₃-(3,5-C₆H₃-(CMe₃)₂)₂), and another five PR₂Ar′ phosphines containing the bulky alkyl groups iPr, c-C₅H₉ or c-C₆H₁₁, in combination with Ar′=Ar , Ar , or Ar ( L1 – L10 ). Steric and electronic parameters have been determined computationally and from IR and X-ray data obtained for the phosphines and for some derivatives, including tricarbonyl and dicarbonyl nickel complexes, Ni(CO)₃(PR₂Ar′) and Ni(CO)₂(PR₂Ar′). In the solid state, the free phosphines PR₂Ar′ adopt one of the three possible structures formally related by rotation around the C_ipso−P bond. Details on their relative energies and on the influence of the free phosphine structure on its coordination chemistry towards Ni(CO)_n (n = 2, 3) fragments has been obtained by experimental and computational methods.     

NMR Self-Diffusion and Transverse Relaxation Time in Bitumen: The Effect of Aging

In this investigation the dynamics of two types of bitumens with different penetration grade were tested by using dynamic shear rheometry (DSR) and Nuclear Magnetic Resonance (NMR) at unaged conditions, and upon both short- and long-term artificial aging. The gel-sol transition temperature was found to increase with increasing the time of aging treatment. Arrhenius parameters of the viscosity were found, unexpectedly, to be correlated with those of simple liquids, suggesting that the two kinds of systems, although chemically and physically quite different, share the same basic process at the molecular level. The molecular dynamics has been then investigated by NMR Pulsed Field Gradient Stimulated-Echo (PFGSE) and relaxometry (Carr-Purcell-Meiboom-Gill, CPMG, spin-echo pulse sequence) to capture the effect of aging upon dynamics variables such as self-diffusion coefficients D and transverse relaxation times T₂. The translational diffusion at T> of the light molecular components of both types of bitumens was characterized by broad distributions of D which were found independent of the experimental time scale up to 0.2 s. Similarly, T₂ data could be described as a continuous unimodal distributions of relaxation times determined both at T< and T> .     

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A copper‐catalyzed aerobic oxidative ring expansion reaction of isatins with 1,2,3,4‐tetrahydroisoquinoline for the synthesis of tetracyclic quinazolinones has been developed. The capacity of the resultant 5H‐isoquinolino[1,2‐b]quinazolin‐8(6H)‐one for a range of palladium‐catalyzed directing C—H activation has been further demonstrated, thus giving a broader access to diverse tetracyclic quinazolinones. More details are discussed in the article by Xiao and Deng et al. on page 87—92.

     

N‐Tosyl‐l‐proline benzene hemisolvate: a rare example of a hydrogen‐bonded carboxylic acid dimer with symmetrically disordered H atoms

The carboxylic acid group is an example of a functional group which possess a good hydrogen‐bond donor (–OH) and acceptor (C=O). For this reason, carboxylic acids have a tendency to self‐assembly by the formation of hydrogen bonds between the donor and acceptor sites. We present here the crystal structure of N‐tosyl‐l ‐proline (TPOH) benzene hemisolvate {systematic name: (2S)‐1‐[(4‐methylbenzene)sulfonyl]pyrrolidine‐2‐carboxylic acid benzene hemisolvate}, C₁₂H₁₅NO₄S·0.5C₆H₆, (I), in which a cyclic R₂²(8) hydrogen‐bonded carboxylic acid dimer with a strong O—(H)…(H)—O hydrogen bond is observed. The compound was characterized by single‐crystal X‐ray diffraction and NMR spectroscopy, and crystallizes in the space group I2 with half a benzene molecule and one TPOH molecule in the asymmetric unit. The H atom of the carboxyl OH group is disordered over a twofold axis. An analysis of the intermolecular interactions using the noncovalent interaction (NCI) index showed that the TPOH molecules form dimers due to the strong O—(H)…(H)—O hydrogen bond, while the packing of the benzene solvent molecules is governed by weak dispersive interactions. A search of the Cambridge Structural Database revealed that the disordered dimeric motif observed in (I) was found previously only in six crystal structures.     

On the Mechanical Properties of Popgraphene-Based Nanotubes: a Reactive Molecular Dynamics Study

Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( and ) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( ). Moreover, it was obtained that Young's modulus (Y_Mod) (750–900 GPa) and ultimate strength (σ_US) (120–150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. Y_Mod values obtained for PopNTs are not significantly temperature-dependent. While the σ_US values for the showed a quasi-linear dependence with the temperature, the exhibited no clear trends.     

Reaction of Pertechnetate in Highly Alkaline Solution: Synthesis and Characterization of the Nitridotrioxotechnetate Ba[TcO3N]

The preparation of novel technetium oxides, their characterization and the general investigation of technetium chemistry are of significant importance, since fundamental research has so far mainly focused on the group homologues. Whereas the structure chemistry of technetium in strongly oxidizing media is dominated by the anion, our recent investigation yielded the new anion. Brown single crystals of Ba[TcO₃N] were obtained under hydrothermal conditions starting from Ba(OH)₂ ⋅ 8H₂O and NH₄[TcO₄] at 200 °C. crystallizes in the monoclinic crystal system with the space group P2₁/n (a=7.2159(4) Å, b=7.8536(5) Å, c=7.4931(4) Å and β=104.279(2)°). The crystal structure of consists of isolated tetrahedra, which are surrounded by Ba²⁺ cations. XANES measurements complement the oxidation state +VII for technetium and Raman spectroscopic experiments on Ba[TcO₃N] single crystals exhibit characteristic Tc−O and Tc−N vibrational modes.     

Au(I)-Catalyzed 6-endo-dig Cyclizations of Aromatic 1,5-Enynes to 2-(Naphthalen-2-yl)anilines Leading to Divergent Syntheses of Benzo[α]carbazole,Benzo[c,h]cinnoline and Dibenzo[i]phenanthridine Derivatives

A gold(I)-catalyzed 6-endo-dig cyclization of aromatic 1,5-enynes was developed to synthesize 2-(naphthalen-2-yl)anilines. The functional group tolerance of this cyclization was examined systematically and a possible mechanism was proposed. The derivatization of 2-(naphthalen-2-yl)aniline was carried out to facile access to benzo[α]carbazole, benzo[c,h]cinnoline and dibenzo[i]phenanthridine derivatives in a divergent way.     

Complexes Featuring a cis-[M U M] Core (M=Rh,Ir): A New Route to Uranium-Metal Multiple Bonds

Although examples of multiple bonds between actinide elements and main-group elements are quite common, studies of the multiple bonds between actinide elements and transition metals are extremely rare owing to difficulties associated with their synthesis. Here we report the first example of molecular uranium complexes featuring a cis-[M U M] core (M=Rh, Ir), which exhibits an unprecedented arrangement of two M U double dative bond linkages to a single U center. These complexes were prepared by the reactions of chlorine-bridged heterometallic complexes [{U{N(CH₃)(CH₂CH₂NPⁱPr₂)₂}(Cl)₂[(μ-Cl)M(COD)]₂}] (M=Rh, Ir) with MeMgBr or MeLi, a new method for the construction of species with U−M multiple bonds. Theoretical calculations including dispersion confirmed the presence of two U M double dative bonds in these complexes. This study not only enriches the U M multiple bond chemistry, but also provides a new opportunity to explore the bonding of actinide elements.     

A Layered Tin Bismuth Selenide with Three Different Building Blocks that Account for an Extremely Large Lattice Parameter of 283 Å

The layered compound Sn_2.8(4)Bi_20.2(4)Se₂₇ exhibits an extraordinarily long-periodic 150R stacking sequence. The crystal structure contains three different building blocks, which form upon the addition of Sn to a Bi-rich bismuth selenide. Sn-doped Bi₂ double (“2”) layers similar to those in elemental bismuth, Sn_0.3Bi_1.7Se₃ quintuple (“5”) layers and Sn_0.4Bi_2.6Se₄ septuple (“7”) layers are arranged in a 7525757525|7525757525|7525757525 sequence, which corresponds to a structure with a=4.1819(4) and c=282.64(6) Å in space group R m. The structure of a microcrystal was determined using microfocused synchrotron radiation and refined as a formally commensurately modulated structure in (3+1)D superspace (superspace group R m(00γ)00), with a trivial basic structure that contains just one atom. The stacking sequence as well as the cation distribution are confirmed by aberration-corrected scanning transmission electron microscopy (STEM) in combination with chemical mapping by X-ray spectroscopy with atomic resolution. Stacking faults are not typical but have been observed occasionally.     

Azobenzene Isomerization-Induced Photomodulation of Electronic Properties of N-Heterocyclic Carbenes

Azobenzene-based protonated N-heterocyclic carbenes (NHCs), N,N’-bis(azobenzene)imidazolium chlorides (IAz-X⋅HCl; X=OMe, Br, H) were successfully synthesized and switching abilities of the attached azobenzene units along with the concomitant photoinduced generation of geometric isomers were studied. Upon irradiation with 365 nm UV light, a p-methoxy-azobenzene derivative get transformed from all-trans isomer to nearly all-cis isomer at the photostationary state. The extent of photomodulation of electronic properties in the NHC ring of the p-methoxy-azobenzene derivative is determined through the Tolman Electronic Parameter (TEP). Iridium complex, [(IAz-OMe)IrCl(CO)₂] was synthesized and infrared spectra were recorded in dichloromethane solution as film in NaCl crystals and by drop-casting in an ATR crystal. Comparison in averaged carbonyl stretching frequency between all-trans isomer ( ) and all-cis isomer ( ) indicates a significant decrement of Δ^tt–cc _av=2.7 cm⁻¹ (film) and 3.8 cm⁻¹ (ATR). Therefore, moderate to excellent enhancement of electron density (Δ^tt–cc TEP=2.3 cm⁻¹ [film] and 3.2 cm⁻¹ [ATR]) at the C-2 position of the NHC is achieved through trans→cis isomerization of the remotely placed azobenzene units. This fine phototuning of electron-donating ability at the catalytic center would pave the way to control NHC/NHC-metal catalyzed organic transformations through external stimuli.     

Indirect Nuclear Spin-Spin Exchange Coupling through Solvated Electron in Small Sizes of Cyclic and Cage-Shaped Perfluoroalkanes

Small perfluorocycloalkanes (hexafluorocyclopropane (c-C₃F₆), octafluorocyclobutane (c-C₄F₈) and decafluorocyclopentane (c-C₅F₁₀) and cage-shaped perfluoroalkanes (perfluoro tetrahedral alkane (C₄F₄), perfluoro prismane (C₆F₆) and perfluoro cubane (C₈F₈)) are better electron scavengers. The captured excess electrons are weakly bound inside their backbone voids or over their backbones, forming the solvated electron ( ) systems (e@c-C_nF_2ns (n=3, 4, 5) and e@C_nF_n (n=4, 6, 8)). There have been many studies on the structures and properties of such systems. However, the effect of on the indirect nuclear spin-spin coupling (J-coupling) is unknown. In this work, we explore how affects ^NeJ-coupling between two coupled F nuclei (^NeJ_FF-coupling) in perfluoroalkane systems through density functional theory calculations. We find unusual trans-^NeJ_FF-couplings (two coupled F nuclei in trans-position) in e@c-C_nF_2n (n=3, 4, 5) and ^NeJ_FF-couplings in e@C_nF_n (n=4, 6, 8). One excess electron not only changes the molecular structures, but also enforces unique distributions and properties, depending on the structural characteristics. We also confirm that such unusual ^NeJ_FF-couplings are realized by through- (T-SE) transmission mechanism, rather than the conventional through-bonds (T−B)/through-space (T−S) ones. The novel transmission mechanism consists of the T-SE coupling path (path 1) and -enhanced T−B T−S coupling path (path 2), and the two paths jointly control ^NeJ_FF through cooperation and competition. Interestingly, the former plays a dominant role for long-range ^NeJ_FF-coupling (N=5), while the latter plays a role in the short-range ^NeJ_FF-coupling (N=3, 4). Path bending angle mainly influences path 1, while path 2 is mainly influenced by the path length. This work not only provides novel insights into the mediating role of in the coupling information exchange, but also proposes a new -based coupling mechanism, possibly opening up potential applications for the -based indirect nuclear spin couplings.     

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The inside back cover picture depicts the inverse-electron-demand Diels–Alder reactions of 2-pyrones with various readily available dihydropyrroles and dihydrofurans. By the catalysis of lanthanide salts, these reactions occur with high yields and enantioselectivities, thus providing a step-economical synthetic platform for densely functionalized cis-hydroindoles and cis-hydrobenzofurans. The synthetic utility of this approach is demonstrated by the concise synthesis of (–)-α-lycorane and (–)-lycorine alkaloids. More details are discussed in the article by Cai et al. on page 21—26.

     

Inside Cover

This review summarizes key development of N‐heterocyclic carbene organic catalysis, with a particular focus on the basic activation and reaction modes enabled by NHCs. More details are discussed in the article by Chi et al. on page 1167—1202.

     

Cover: Journal of the Chinese Chemical Society 11/2019

In this paper, a series of novel substituted (E)‐N′‐benzylidene‐4‐methyl‐2‐(2‐propylpyridin‐4‐yl)thiazole‐5‐carbohydrazide derivatives have been synthesized. The synthesized compounds were screened for their in vitro antimicrobial and antioxidant activities. Among the screened compounds, 6b, 6e, 6j and 6k were found to be more promising antimicrobial agents. 2, 2‐Diphenyl‐1‐picrylhydrazyl assay was used to test the antioxidant activities of the carbohydrazides and compounds 6b and 6i have shown better free‐radical scavenging ability. More details about this figure will be discussed by Dr. K. P. Haval and his group on page 1507–1517 in this issue.

     

Isolation and structure of an 18‐membered macrocycle containing two diselenide linkages and its precursor

The structures of the 18‐membered diselenide‐linked macrocycle 10,27‐di‐tert‐butyl 11,28‐dioxo‐2,3,19,20‐tetraselena‐10,12,27,29‐tetraazapentacyclo[28.4.0.0^4,9.0^13,18.0^21,26]tetratriaconta‐1(30),4(9),5,7,13,15,17,21,23,25,31,33‐dodecaene‐10,27‐dicarboxylate, C₃₆H₃₄N₄O₆Se₄, and its precursor di‐tert‐butyl 2,2′‐[diselane‐1,2‐diylbis(2,1‐phenylene)]dicarbamate, C₂₂H₂₈N₂O₄Se₂, are reported. The precusor to the macrocycle contains two tert‐butyl phenylcarbamate arms connected to a diselenide group, with Se—C and Se—Se bond lengths of 1.914 (4) and 2.3408 (6) Å, respectively. The macrocycle resides on a crystallographic center of inversion in space group P with one molecule in the unit cell (Z′ = ). It contains an 18‐membered macrocyclic ring with two diselenide linkages. In this macrocycle, there are two free and two protected amino groups.     

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Regioselective Csp³–H and Csp²–H alkynylation under Ir(III) and Ag(I) catalytic system was developed by judicious choice of readily available and structurally modifiable ketoximes and amides as the key substrates. Key features of this transformation included: 1) For ketoxime substrates, only primary Csp³–H at γ position to the nitrogen atom of ketoximes could readily undergo this Csp³–H alkynylation under Ir(III) catalysis. Notably, by slight modification of the structure of substrates, alcohols and ketones derived ketoximes could well participate in this transformation. 2) For amide substrates, primary phenylacetamides, which are challenging substrates due to the tautomerization of the distal O‐coordinating acetamides, could well serve as suitable substrates for the Csp²–H alkynylation. Significantly, when using oxidizing amides as the directing groups, α,β‐dehydrogenative C—H alkynylation was achieved. More details are discussed in the article by Shi et al. on page 929—934.

     

LaTe1.82(1): modulated crystal structure and chemical bonding of a chalcogen‐deficient rare earth metal polytelluride

Crystals of the rare earth metal polytelluride LaTe_1.82(1), namely, lanthanum telluride (1/1.8), have been grown by molten alkali halide flux reactions and vapour‐assisted crystallization with iodine. The two‐dimensionally incommensurately modulated crystal structure has been investigated by X‐ray diffraction experiments. In contrast to the tetragonal average structure with unit‐cell dimensions of a = 4.4996 (5) and c = 9.179 (1) Å at 296 (1) K, which was solved and refined in the space group P4/nmm (No. 129), the satellite reflections are not compatible with a tetragonal symmetry but enforce a symmetry reduction. Possible space groups have been derived by group–subgroup relationships and by consideration of previous reports on similar rare earth metal polychalcogenide structures. Two structural models in the orthorhombic superspace group, i.e.Pmmn(α,β,)000(?α,β,)000 (No. 59.2.51.39) and Pm2₁n(α,β,)000(?α,β,)000 (No. 31.2.51.35), with modulation wave vectors q₁ = αa* + βb* + c* and q₂ = ?αa* + βb* + c* [α = 0.272 (1) and β = 0.314 (1)], have been established and evaluated against each other. The modulation describes the distribution of defects in the planar [Te] layer, coupled to a displacive modulation due to the formation of different Te anions. The bonding situation in the planar [Te] layer and the different Te anion species have been investigated by density functional theory (DFT) methods and an electron localizability indicator (ELI‐D)‐based bonding analysis on three different approximants. The temperature‐dependent electrical resistance revealed a semiconducting behaviour with an estimated band gap of 0.17 eV.     

Engineering of super bactericidal cotton using pyridinium/di-N-chloramine siloxane with intensified synergism

Tuning the ratio of complementary biocidal groups in a composite unit is proved to be a tactic to better minimize their weaknesses to realize higher synergism. A silane with precursors of one pyridinium and two N-chloramine sites, 6-(pyridin-4-yl)-3-(3-(trimethoxysilyl)propyl)-1,3,5-triazinane-2,4-dione, was synthesized, hydrolyzed and dehydrocondensed into a silicone modifier on cotton cellulose. Specially, isonicotinaldehyde was ammonolyzed with biuret to produce 6-(pyridin-4-yl)-1,3,5-triazinane-2,4-dione that subsequently reacted with (γ-chloropropyl)trimethoxysilane to synthesize the silane through nucleophilic substitution. The modifier on cotton was quaternized and chlorinated to transform the one pyridine and two amide N–H structures in each unit of the silicone to pyridinium and N-chloramine counterparts. The cationic pyridinium increases the hydrophilicity of the unit and draws anionic bacteria to its two adjacent highly fatal N-chloramine sites, achieving a faster contact-killing rate than not only monofunctionality but also basic synergistic integration of one cationic center and one N-chloramine. This phenomenon is therefore referred to as “intensified synergism” and provides crucial information for the design of more powerful biocides. The pyridinium/di-N-chloramine silicone coating exhibited extraordinary durability towards UV irradiation, washing cycles and long-term storage due to the good UV resistance and chemical inertness of pyridinium and silicone backbone.

Graphic abstract

     

A Density Functional Theory Study on Nonlinear Optical Properties of Double Cage Excess Electron Compounds: Theoretically Design M[Cu(Ag)@(NH3)n](M = Be,Mg and Ca; n = 1–3)

In this work, we investigated the nonlinear optical (NLO) properties of excess electron electride molecules of M[Cu(Ag)@(NH₃)_n](M = Be, Mg and Ca; n = 1–3) using density functional theory (DFT). This electride molecules consist of an alkaline-earth (Be, Mg and Ca) together with transition metal (Cu and Ag) doped in NH₃ cluster. The natural population analysis of charge and their highest occupied molecular orbital suggests that the M[Cu(Ag)@(NH₃)_n] compound has excess electron like alkaline-earth metal form double cage electrides molecules, which exhibit a large static first hyperpolarizability () (electron contribution part) and one of which owns a peak value of 216,938 (a.u.) for Be[Ag@(NH₃)₂] and vibrational harmonic first hyperpolarizability () (nuclear contribution part) values and the ratio of /, namely, η values from 0.02 for Be[Ag@(NH₃)] to 0.757 for Mg[Ag@(NH₃)₃]. The electron density contribution in different regions on values mainly come from alkaline-earth and transition metal atoms by first hyperpolarizability density analysis, and also explains the reason why values are positive and negative. Moreover, the frequency-dependent values β(−2ω,ω,ω) are also estimated to make a comparison with experimental measures. © 2018 Wiley Periodicals, Inc.