Air-stable Compounds Research Articles

Silicon Analogues of Cyclopropyl Radical Derived from a Highly Stable Cyclic Disilene Compound Featuring a Si-Br Bond.

A halogen-substituted cyclic disilene compound, bromocyclotrisilene, Si3Br(Eind)3 (3a), bearing fused-ring bulky Eind (a: R1 = R2 = Et) groups, has been synthesized as an extraordinarily air-stable compound by the reduction of 1,2-dibromodisilene, (Eind)BrSi═SiBr(Eind) (2a), or tribromosilane, (Eind)SiBr3 (1a), with the Mg or Li metal. The X-ray diffraction analysis of 3a showed that the disilene moiety has an almost planar, but slightly trans-bent structure. Even though 3a is quite air-stable both in solutions and in the solid state, its Si-Br bond is reactive under reducing conditions. The further treatment of 3a with the Li metal leads to the formation of room-temperature thermally stable silicon homologues of the cyclopropyl radical, i.e., the cyclotrisilanyl radicals (6a) [6a(syn) and 6a(anti)], via intramolecular C-H bond activation in a transient silicon homologue of the cyclopropenyl radical, i.e., the cyclotrisilenyl radical, [Si3(Eind)3]• (5a). The formation mechanism of 6a from 5a is discussed based on the theoretical calculations. The unique structural and electronic properties of these Si3 three-membered ring species incorporating the Eind groups have been experimentally and theoretically investigated.

Design Rules, Accurate Enthalpy Prediction, and Synthesis of Stoichiometric Eu3+ Quantum Memory Candidates.

Stoichiometric Eu3+ compounds have recently shown promise for building dense, optically addressable quantum memory as the cations' long nuclear spin coherence times and shielded 4f electron optical transitions provide reliable memory platforms. Implementing such a system, though, requires ultranarrow, inhomogeneous linewidth compounds. Finding this rare linewidth behavior within a wide range of potential chemical spaces remains difficult, and while exploratory synthesis is often guided by density functional theory (DFT) calculations, lanthanides' 4f electrons pose unique challenges for stability predictions. Here, we report DFT procedures that reliably reproduce known phase diagrams and correctly predict two experimentally realized quantum memory candidates. We are the first to synthesize the double perovskite halide Cs2NaEuF6. It is an air-stable compound with a calculated band gap of 5.0 eV that surrounds Eu3+ with mononuclidic elements, which are desirable for avoiding inhomogeneous linewidth broadening. We also analyze computational database entries to identify phosphates and iodates as the next generation of chemical spaces for stoichiometric quantum memory system studies. This work identifies new candidate platforms for exploring chemical effects on quantum memory candidates' inhomogeneous linewidth while also providing a framework for screening Eu3+ compound stability with DFT.

Modified aryldifluorophenylsilicates with improved activity and selectivity in nucleophilic fluorination of secondary substrates.

Nucleophilic fluorination of secondary aliphatic substrates, especially of halides, still remains a challenge. Among the available reagents, TBAT belongs to one of the best choices due to its stability, affordable price and low toxicity. With the aim to improve its selectivity, we synthesized three analogues modified in the aryl part of the TBAT reagent with one or two electron donating methoxy groups or with one electron withdrawing trifluoromethyl group. All three reagents are air-stable compounds and their structure was confirmed by a single crystal X-ray analysis. In testing the reactivity and selectivity of the reagents with a library of secondary bromides, as well as of other selected primary and secondary substrates, we found that substitution with methoxy groups mostly improves both reactivity and selectivity compared to TBAT, while the substitution with trifluoromethyl group leads to inferior results. Difluorosilicates modified by more than two electron donating methoxy groups proved to be unstable and decomposed spontaneously to the HF2 - anion. DFT calculations of tetramethylammonium analogues of the studied reagents disclosed that the substitution of the phenyl group with the methoxy substituent lowers the transitions state energy of the decomposition to a fluorosilane-fluoride complex, while the substitution with the trifluoromethyl group has an opposite effect.

Cyclo-penta-dienone triisocyanide iron complexes: general synthesis and crystal structures of tris-(2,6-di-methyl-phenyl isocyanide)(η4-tetra-phenyl-cyclo-penta-dienone)iron and tris-(naphthalen-2-yl iso-cyanide)(η4-tetra-phenyl-cyclo-penta-dienone)iron acetone hemisolvate.

Irradiation of a toluene solution containing cyclo-penta-dienone tricarbonyl iron complexes and isocyanides with blue LEDs afforded the formation and isolation of 12 triisocyanide complexes, two of which, namely tris-(2,6-di-methyl-phenyl isocyanide)(η4-tetra-phenyl-cyclo-penatedienone)iron, [Fe(C9H9N)3(C29H20O)], and tris-(naphthalen-2-yl isocyanide)(η4-tetra-phenyl-cyclo-penatedienone)iron acetone hemisolvate, [Fe(C11H7N)3(C29H20O)]2·C3H6O, could be characterized crystallographically. The air-stable compounds were purified by column chroma-tography and were characterized by 1H NMR, 13C NMR, elemental analysis and HRMS. NMR and XRD data indicate generally more electron-rich Fe0 centers compared to the corresponding tricarbonyl compounds.

Origins and cavity-based regulation of optical anisotropy of α-MoO3 crystal

Orthogonal α-MoO3 is one of the most common and air-stable compounds of molybdenum, holding the merits of wide bandgap, van der Waals (vdW) structure, biaxial symmetry and recently discovered hyperbolic topological transitions, which has drawn significant attention in developing novel nanophotonic and optoelectronic devices. Herein the broadband optical anisotropy, one of the most fundamental physical characteristics of α-MoO3 crystal, was systematically investigated using a combination of spectroscopic ellipsometry (SE) and reflectance difference spectroscopy (RDS). The centimeter-level high-quality α-MoO3 crystal was grown by modified physical vapor deposition. The optical refractive indices along three crystalline axes were precisely determined by SE in the broad spectral range (400–1600 nm), and then the in-plane and out-plane birefringence was analyzed. Both the intrinsic and resonant cavity modulated optical anisotropy of α-MoO3 was studied by polarization-resolved RDS, from which we find the physical origins of linear dichroism are dominated by electronical transitions along the c-axis. Furthermore, the external photonic cavity of SiO2 enables enhanced sensitivity to view electronical transitions and a high modulation ratio of optical anisotropy reached 30, which provides new opportunities to tune optical anisotropy for polarized photonic devices. Our results can help understand the physical origin of the highly optical anisotropy of α-MoO3 and establish an effective metrological tool to study other types of vdW crystals.

Redox Active cAAC-Fluorene/Indene Systems Displaying Solvatochromism, Green Luminescence and pH Sensing: Functionalization of Fluorenyl/Indenyl Rings with Radical Carbene.

Two new series of air stable compounds of cAACX = fluorene/indene (X = Me2 , Et2 , Cy) [cAAC = cyclic (alkyl) amino carbene] have been isolated and well characterized by X-ray single crystal diffraction, photoluminescence, cyclic voltammogram (CV) and electron paramagnetic resonance (EPR) studies. Fluorescence studies reveals green light emission of cAAC bonded fluorene, whereas free fluorene generally displays a violet emission. Interestingly, the sterically crowded cAAC-fluorene analogue display solvatochromism and CF3 CO2 H sensing in solution. CV of the these compounds show a quasi-reversible electron transfer process, indicating the functionalization of fluorene/indene with radical anionic form of carbene, confirmed by CV/EPR measurements. DFT/TDDFT calculations and energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV) have been carried out to study different aspects of bonding and electronic transitions. Such a class of redox active and thermally stable organic molecules may be suitable for molecule based spin memory devices in future.

Synthesis, Crystal Structure, and Broadband Emission of (CH3)3SSnCl3.

We report here on the synthesis, crystal structure, optoelectronic and vibrational properties, as well as the DFT calculations of the novel trimethylsulfonium tin trichloride (CH3)3SSnCl3. The air-stable compound is prepared by reacting the (CH3)3SCl and SnCl2 solid precursors in evacuated silica tubes at 100 °C. According to powder X-ray diffraction and Rietveld refinement, it crystallizes at room temperature in the orthorhombic space group Pbca (No. 61) with isolated pyramids of [SnCl3]- and (CH3)3S+ units. UV-vis reflectance and photoluminescence spectroscopies reveal a direct energy band gap of 3.85 eV, accompanied by a broad Stokes-shifted luminescence signal. Photoexcitation of the compound at room temperature and at -196 °C results in broadband luminescence with weak magenta emission centered at 400 nm using an excitation at 250 nm. First principal calculations provide insight into the physical properties through the electron and phonon density of states. Multitemperature Raman spectroscopy and differential scanning calorimetry reveal a reversible phase transition at ca. 70 °C that affects the vibrational modes of the [SnCl3]-. By dissolving (CH3)3SSnCl3 in dimethylformamide in ambient air for a week, oxidation of tin occurs in the "defect" perovskite ((CH3)3S)2SnCl6. The crystal structure of ((CH3)3S)2SnCl6 is also determined with high accuracy via single-crystal X-ray diffraction (cubic space group Pa-3 (No. 205)) and compared with (CH3)3SSnCl3 via Hirshfeld surface analysis.

Cobaltoceniumselenolate Gold(I) Complexes: Synthesis, Spectroscopic, Structural and Anticancer Properties.

Cobaltoceniumselenolate is an unusual, highly air‐sensitive, mesoionic compound containing a very soft anionic selenium donor atom. Here we explore its coordination chemistry with Au(I) metal centers and show that its hetero‐ and homoleptic gold complexes are highly colored, air‐stable compounds, which were characterized by 1H/13C/31P/77Se NMR, IR, UV‐Vis, HR‐MS and single crystal XRD. Cytotoxicity of these polar, water‐soluble complexes was studied against various standard cancer cell lines (A549MDA‐MB‐231, HT‐29) revealing good anticancer activity of all three complexes.

Synthesis, characterization and fluorescent properties of ferrocenyl pyrazole and triazole ligands and their palladium complexes

The search for new fluorescent materials with high quantum yields has been the focus of research, considering the diverse applications that fluorescent materials present. In this study, ferrocenyl pyrazolyl (L1) and ferrocenyl triazolyl (L2) ligands and their palladium metal complexes (1 and 2) were synthesized to investigate their fluorescence properties. While the pyrazolyl ligand was prepared through a ligand substitution reaction, synthesis of the triazolyl derivative involved the [3 + 2] azide-alkyne using click chemistry. All the prepared compounds have been characterized by NMR and IR spectroscopy, elemental analysis, mass spectrometry and single-crystal X-ray crystallography. These air-stable compounds were prepared in moderate to good yields (70% and 83%).The ferrocenyl-pyrazolyl L1 and ferrocenyl-triazolyl L2 ligands showed near-infrared (NIR) emission bands with quantum yields of 20% and 26% respectively. The addition of the Pd2+ ions results in the reduction of fluorescence intensity and quantum yield. Such fluorescent properties demonstrate their potential use in bio-analysis and as fluorogenic probing.

Mono-, Di- and Tetra-iron Complexes with Selenium or Sulphur Functionalized Vinyliminium Ligands: Synthesis, Structural Characterization and Antiproliferative Activity.

A series of diiron/tetrairon compounds containing a S- or a Se-function (2a–d, 4a–d, 5a–b, 6), and the monoiron [FeCp(CO){SeC1(NMe2)C2HC3(Me)}] (3) were prepared from the diiron μ-vinyliminium precursors [Fe2Cp2(CO)( μ-CO){μ-η1: η3-C3(R’)C2HC1N(Me)(R)}]CF3SO3 (R = R’ = Me, 1a; R = 2,6-C6H3Me2 = Xyl, R’ = Ph, 1b; R = Xyl, R’ = CH2OH, 1c), via treatment with S8 or gray selenium. The new compounds were characterized by elemental analysis, IR and multinuclear NMR spectroscopy, and structural aspects were further elucidated by DFT calculations. The unprecedented metallacyclic structure of 3 was ascertained by single crystal X-ray diffraction. The air-stable compounds (3, 4a–d, 5a–b, 6) display fair to good stability in aqueous media, and thus were assessed for their cytotoxic activity towards A2780, A2780cisR, and HEK-293 cell lines. Cyclic voltammetry, ROS production and NADH oxidation studies were carried out on selected compounds to give insights into their mode of action.

A New Three-Dimensional Subsulfide Ir2In8S with Dirac Semimetal Behavior

Dirac and Weyl semimetals host exotic quasiparticles with unconventional transport properties, such as high magnetoresistance and carrier mobility. Recent years have witnessed a huge number of newly predicted topological semimetals from existing databases; however, experimental verification often lags behind such predictions. Common reasons are synthetic difficulties or the stability of predicted phases. Here, we report the synthesis of the type-II Dirac semimetal Ir2In8S, an air-stable compound with a new structure type. This material has two Dirac crossings in its electronic structure along the Γ-Z direction of the Brillouin zone. We further show that Ir2In8S has a high electron carrier mobility of ∼10 000 cm2/(V s) at 1.8 K and a large, nonsaturating transverse magnetoresistance of ∼6000% at 3.34 K in a 14 T applied field. Shubnikov de-Haas oscillations reveal several small Fermi pockets and the possibility of a nontrivial Berry phase. With its facile crystal growth, novel structure type, and striking electronic structure, Ir2In8S introduces a new material system to study topological semimetals and enable advances in the field of topological materials.

A novel fluorescent sensors for sensitive detection of nitrite ions

In this work, the fluorescent sensors based ternary ZnCdS quantum dots (QDs) were constructed for nitrite (NO2−) detection, and ternary ZnCdS QDs were synthesized by a rather facile, low-cost and effective aqueous synthesis method using air-stable compounds. Experimental results indicated that the ZnCdS QDs fluorescence (PL) emission intensity was decreased gradually with the introduction of NO2−. Importantly, the F/F0 (F and F0 were the PL intensity in the presence and absence of NO2− at 505 nm, respectively) was linearly proportional to the NO2− to 700 μM, the equation of linear regression was y = −0.123x+1.1525, which showed a better performance to the detection of NO2−. Moreover, there was no interference to other interfering substances including metal ions and anion ions. Thus, we applied the ZnCdS QDs fluorescence sensors to detect the contents of NO2− in ham sausage and the results showed that the contents of NO2− in ham sausage was 18.45 mg/kg. Therefore, this test method had the advantages of simplicity, rapidity and high sensitivity.

Structure and stability of n- and p-type intercalated multilayer graphene using Cs-C2H4, FeCl3 and MoCl5

Multilayer graphene (MLG) sheets have found a wide variety of applications in the field of electronics. However, the electrical resistivity of MLG sheets is much higher than that of metals. Although some attempts have been undertaken to intercalate compounds such as FeCl3 into MLG in order to reduce resistivity, the stabilities of the resulting products were not always sufficient. Further, there have been few reports of air-stable intercalated MLGs with n-type conduction.In this study, we used three types of MLGs: MLGs synthesized via CVD with four graphene layers, those with over 30 layers, and exfoliated MLG from HOPG. Regarding the n-type compound, the co-intercalation of Cs and C2H4 into these MLGs was performed, and the structures and air-stabilities of the reaction products were determined. Meanwhile, for the p-type compound, the intercalation of MoCl5 and FeCl3 were also investigated. The Cs-C2H4-MLG were sufficiently stable, such that the initial stage-2 structure was maintained for four weeks in air. Further, the resistivity dropped to one fourth that of the MLG. Although MoCl5 and FeCl3 could be intercalated to MLGs, MoCl5 was more suitable to form air-stable compounds.

Zn/Cd ratio-dependent synthetic conditions in ternary ZnCdS quantum dots

In our study, the synthesis conditions of ternary alloyed ZnCdS quantum dots (QDs) with different Zn/Cd molar ratios were investigated. Our results indicated that the optimal reaction conditions of ZnCdS QDs with various molar ratios were different. The ternary ZnCdS QDs were synthesized by a rather simple, facile, low-cost and effective aqueous synthesis method using air-stable compounds. UV–visible (UV–Vis) absorbance and photoluminescence (PL) emission spectra of the ZnCdS QDs showed a blue shift with the decrease of Cd, indicating the formation of alloyed QDs. The optimal reaction conditions, such as refluxing time and S/(Zn+Cd) molar ratios were different for ZnCdS QDs with different Zn/Cd ratios. The cause of the difference was attributed to the different properties of metal ions. In addition, the investigation on the photostability showed that the as-prepared ternary alloyed QDs had strong light resistance. Therefore, the ternary alloyed QDs with outstanding optical properties and high photostability showed potential biological applications and the results also offered new insights for the synthesis of ZnCdS QDs.

A Terminal Fluoride Ligand Generates Axial Magnetic Anisotropy in Dysprosium Complexes.

The first dysprosium complexes with a terminal fluoride ligand are obtained as air-stable compounds. The strong, highly electrostatic dysprosium-fluoride bond generates a large axial crystal-field splitting of the J=15/2 ground state, as evidenced by high-resolution luminescence spectroscopy and correlated with the single-molecule magnet behavior through experimental magnetic susceptibility data and ab initio calculations.

Trimethylsulfonium Lead Triiodide: An Air-Stable Hybrid Halide Perovskite.

We report on the synthesis, characterization, and optoelectronic properties of the novel trimethylsulfonium lead triiodide perovskite, (CH3)3SPbI3. At room temperature, the air-stable compound adopts a hexagonal crystal structure with a 1D network of face-sharing [PbI6] octahedra along the c axis. UV-vis reflectance spectroscopy on a pressed pellet revealed a band gap of 3.1 eV, in agreement with first-principles calculations, which show a small separation between direct and indirect band gaps. Electrical resistivity measurements on single crystals indicated that the compound behaves as a semiconductor. According to multi-temperature single-crystal X-ray diffraction, synchrotron powder X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry, two fully reversible structural phase transitions occur at -5 and ca. -100 °C with reduction of the unit cell symmetry to monoclinic as temperature decreases. The role of the trimethylsulfonium cation regarding the chemical stability and optoelectronic properties of the new compound is discussed in comparison with APbI3 (A = Cs, methylammonium, and formamidinium cation), which are most commonly used in perovskite solar cells.

Cu(II) Coordination Polymers as Vehicles in the A3 Coupling.

A family of benzotriazole based coordination compounds, obtained in two steps and good yields from commercially available materials, formulated as [CuII(L1)2(MeCN)2]·2ClO4·MeCN (1), [CuII(L1)(NO3)2]·MeCN (2), [ZnII(L1)2(H2O)2]·2ClO4·2MeCN (3), [CuII(L1)2Cl2]2 (4), [CuII5(L1)2Cl10] (5), [CuII2(L1)4Br2]·4MeCN·CuII2Br6 (6), [CuII(L1)2(MeCN)2]·2BF4 (7), [CuII(L1)2(CF3SO3)2] (8), [ZnII(L1)2(MeCN)2]·2CF3SO3 (9), [CuII2(L2)4(H2O)2]·4CF3SO3·4Me2CO (10), and [CuII2(L3)4(CF3SO3)2]·2CF3SO3·Me2CO (11), are reported. These air-stable compounds were tested as homogeneous catalysts for the A3 coupling synthesis of propargylamine derivatives from aldehyde, amine, and alkyne under a noninert atmosphere. Fine tuning of the catalyst resulted in a one-dimensional (1D) coordination polymer (CP) (8) with excellent catalytic activity in a wide range of substrates, avoiding any issues that would inhibit its performance.

Stable (sila)difluoromethylboranes via C-F activation of fluoroform derivatives.

Lithium 1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaborol-2-uide activates the C-F linkage of fluoroform (CF3H) and the Ruppert-Prakash reagent (CF3SiMe3) to provide difluoromethyl-substituted boranes as air-stable compounds.

Bismuth Iodide Perovskite Materials for Solar Cell Applications: Electronic Structure, Optical Transitions, and Directional Charge Transport

Cesium and methylammonium bismuth iodides (Cs3Bi2I9 and MA3Bi2I9) are new low-toxic and air stable compounds in the perovskite solar cell family with promising characteristics. Here, the electronic structure and the nature of their optical transitions, dielectric constant, and charge carrier properties are assessed for photovoltaic applications with density functional theory (DFT) calculations and experiments. The calculated direct and indirect band gap values for Cs3Bi2I9 (2.17 and 2.0 eV) and MA3Bi2I9 (2.17 and 1.97 eV) are found to be in good agreement with the experimental optical band gaps (2.2, 2.0 eV and 2.4, 2.1 eV for Cs3Bi2I9 and MA3Bi2I9, respectively) estimated for solution-processed films. There is an error cancelation in the DFT calculated band gap similar to that for lead perovskites. However, fully relativistic DFT calculations indicate that the size of the spin orbit coupling (SOC) error cancelation for bismuth perovskite (0.5 eV) is less than for lead perovskite (1 eV), and other factors...

Optical-Vibrational Properties of the Cs2SnX6(X = Cl, Br, I) Defect Perovskites and Hole-Transport Efficiency in Dye-Sensitized Solar Cells

We report the vibrational and optical properties of the ‘defect’ perovskites Cs2SnX6 (X = Cl, Br, I) as well as their use as hole-transporting materials (HTMs) in solar cells. All three air-stable compounds were characterized using powder X-ray diffraction and Rietveld refinement. Far-IR reflectance, Raman, and UV–vis spectroscopy as well as electronic band structure calculations show that the compounds are direct band gap semiconductors with a pronounced effect of the halogen atom on the size of the energy gap and the vibrational frequencies. Scanning electron microscopy and atomic force microscopy confirmed that the morphology of the perovskite films deposited from N,N-dimethylformamide solutions on TiO2 substrates also strongly depends on the chemical composition of the materials. The Cs2SnX6 perovskites were introduced as hole-transporting materials in dye-sensitized solar cells, based on mesoporous titania electrodes sensitized with various organic and metal–organic dyes. The solar cells based on Cs2...