Alkanethiol monolayers at reduced and oxidized zinc surfaces with corrosion protection: a sum frequency generation and electrochemistry investigation

In this work, octadecanethiol (ODT) was demonstrated to form ordered monolayers at either electrochemically reduced or oxidized Zn surfaces, by means of sum frequency generation (SFG) spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The SFG spectra of ODT-modified Zn electrodes featured three methyl group resonances in the C-H vibrational region (2800-3100 cm(-1)). A significant decrease in interfacial capacitance and an increase in charge-transfer resistance were observed in EIS measurement after ODT modification. The alkane chain tilt angle of ODT within a monolayer at the Zn surface was estimated as 0 degrees with respect to the surface normal by interfacial capacitance measurement via EIS. CV and SFG investigation revealed that ODT monolayers undergo reductive desorption from the Zn electrode in 0.5 M NaOH at -1.66 V (vs SCE) and in 0.5 M NaClO4 at -1.62 V. The integrated charge consumed to the desorption of ODT is determined as 87 mC/cm2 from the reductive peak on CV curve, resulting in a coverage of 9.0 x 10(-10) mol/cm2 (5.4 x 10(14) molecules/cm2) if assuming the reduction follows a one-electron process. ODT monolayers show corrosion protection to underlying zinc at the early immersion stage in base, salt, and acid media. However, the protection efficiency was reduced with immersion time due to the presence of defects within the monolayers.     

Ba4Ca(B2O5)2F2: π-conjugation of B2O5 in the planar pentagonal layer achieving large second harmonic generation of pyro-borate

The nonlinear optical (NLO) crystals that can expand the wavelength of the laser to the deep-ultraviolet (DUV) region by the cascaded second harmonic generation (SHG) are of current research interest. It is well known that borates are the most ideal material class for the design of new DUV NLO crystals owing to the presence of good NLO genes, e.g., BO₃ or B₃O₆ groups. However, the NLO pyro-borates with the B₂O₅ dimers as the sole basic building units are still rarely reported owing to their small SHG responses. In this communication, by constructing a planar pentagonal [Ca(B₂O₅)]_∞ layer, the NLO pyro-borate Ba₄Ca(B₂O₅)₂F₂ with a large SHG response (∼2.2 × KDP, or ∼7 × α-Li₄B₂O₅) and a DUV transparent window has been designed and synthesized. The first-principles calculations show that the large SHG response of Ba₄Ca(B₂O₅)₂F₂ mainly originates from the better π-conjugation of the coplanar B₂O₅ dimers in the [Ca(B₂O₅)]_∞ layer. In addition, the planar pentagonal pattern in the [Ca(B₂O₅)]_∞ layer provides an ideal template for designing the new DUV NLO crystals, apart from those in known DUV borates, e.g., the [Be₂BO₃F₂]_∞ layer in KBe₂BO₃F₂ (KBBF).

A new deep-UV NLO pyro-borate Ba₄Ca(B₂O₅)₂F₂ was synthesized by solid-state reactions. The better π-conjugation of B₂O₅ dimers in the planar pentagonal layer achieves a large SHG response (∼2.2 × KDP), which is the largest among all the known DUV transparent borates with B₂O₅ units.

Deep-ultraviolet (DUV, λ < 200 nm) coherent lights with high photon energy, high spatial resolution, and a small heat-affected zone are of significance for applications in photolithography, high-resolution spectroscopy, laser cooling, and scientific equipment.^1–4 However, it is difficult or well-nigh impossible for solid-state lasers to directly radiate the DUV coherent lights. In contrast, relying on the process of second harmonic generation (SHG) of nonlinear optical (NLO) crystals is a more effective way to generate the DUV coherent lights and causes much attention.^5,6 Therefore, the NLO crystal has become an important material basis of solid-state lasers, which seriously affects the development of all-solid-state laser technology. However, it is still a great challenge to rationally design and synthesize DUV NLO crystals because of the extremely rigorous requirements of structural symmetry and properties.^7–10 Structurally, the DUV NLO crystals must crystallize in the noncentrosymmetric (NCS) space groups which are the prerequisite for the materials to exhibit SHG responses. Moreover, it should possess a broad transparency window, a largely effective NLO coefficient (d_eff ≥ 0.39 pm V⁻¹), and a moderate birefringence (0.05–0.10@1064 nm) to achieve the phase-matching (PM) conditions in the DUV region.¹⁰ Based on these requirements, borates have been considered as the ideal material class for DUV NLO crystals because of their special structure and properties'' virtues, including the rich acentric structural types, large band gaps, and stable physical and chemical properties.⁸ To date, the commercialized borate-based UV NLO crystals consist of β-BaB₂O₄ (BBO), LiB₃O₅ (LBO), CsLiB₆O₁₀ (CLBO),^9,10 and the practical DUV NLO crystal KBe₂BO₃F₂ (KBBF). Especially for KBBF, it has become the sole material that can generate DUV coherent laser light (177.3 nm) by a direct SHG method.⁷ Other excellent borate-based UV NLO crystals also consist of K₃B₆O₁₀Cl,¹¹ SrB₅O₇F₃,¹² Li₂B₆O₉F₂,⁵ CsAlB₃O₆F,¹³ M₂B₁₀O₁₄F₆ (M = Ca, Sr),¹⁴ NH₄B₄O₆F,¹⁵ NaSr₃Be₃B₃O₉F₄,¹⁶ AB₄O₆F (A = K, Rb, and Cs),¹⁷etc.The above borate-based materials have achieved great success as UV and DUV NLO crystals, which are mainly attributed to the ability of boron atoms to coordinate with three or four oxygen anions forming trigonal-planar or tetrahedral building blocks.^18,19 For example, the first borate-based NLO crystal, KB₅O₈·4H₂O (KB₅), has the basic building units (BBUs) of [B₅O₁₀], while the BBUs of β-BBO, LBO, and KBBF are [B₃O₆], [B₃O₇], and isolated [BO₃], respectively.^7,8 Remarkably, although various borate crystals with different types of borate groups have been explored during the past decades, the pyro-borate NLO crystals with B₂O₅ groups as the sole BBUs are rarely reported owing to their weak SHG responses.^20–23 For example, the SHG response of the DUV transparent α-Li₄B₂O₅ (ref. 23) is only ∼0.3 × KDP, which is far smaller than the expected value (0.39 pm V⁻¹, 1 × KDP).Actually, the flexible B₂O₅ groups which are composed of two π-conjugated BO₃ units through corner-sharing may also be capable of generating excellent optical performance if they have benign arrangements. In recent research, Pan''s group has indicated that the B₂O₅ dimers are perfect for the design of DUV birefringent crystals. By the synergistic combination, they have successfully designed a potential pyro-borate birefringent crystal, Li₂Na₂B₂O₅, with a short UV cut-off edge (181 nm) and large birefringence (0.095@532 nm).²¹ And they have also grown Ca(BO₂)₂ crystals exhibiting a short UV cut-off edge and larger birefringence (169 nm; 0.2471@193 nm). Based on the analysis of the structure–property relationship of Ca(BO₂)₂, they stated that the polymerized planar B_nO_2n+1 groups, e.g., B₂O₅, could generate a larger anisotropy than isolated BO₃.²² However, their opposite arrangements of B–O groups make them crystallize in the centrosymmetric (CS) space groups, which limit their further development as NLO compounds. Thus, it is clear that pyro-borates exhibiting a large birefringence and a short UV cut-off edge would also be promising DUV NLO crystals if their SHG responses can be enhanced.Based on the above-mentioned ideas, a systematical investigation has been performed on DUV pyroborates. And finally, we successfully synthesized a new NCS pyro-borate, Ba₄Ca(B₂O₅)₂F₂, which can exhibit not only a large SHG response (∼2.2 × KDP and ∼7 × α-Li₄B₂O₅) but also a short UV cut-off edge (<190 nm). Analyzing its structure, one can find that its excellent NLO properties mainly originate from the unique planar pentagonal [Ca(B₂O₅)]_∞ layer, where the B₂O₅ groups adopt the almost coplanar configurations that favor the structure to generate large SHG response and birefringence,²¹ meanwhile the terminal O atoms of B₂O₅ groups are also linked by the Ca²⁺ cations, which eliminate the dangling bonds of B₂O₅ groups and further blue-shift the UV cut-off edge. More importantly, the adjacent [Ca(B₂O₅)]_∞ layers in Ba₄Ca(B₂O₅)₂F₂ are linked by other B₂O₅ groups to form a 3D framework, which will be favorable for the material to avoid the layer habit that KBBF suffers from. In this sense, the planar pentagonal [Ca(B₂O₅)]_∞ layer is similar to the [Be₂BO₃F₂]_∞ layer in KBBF, and it can be seen as a new structure template for the design of new DUV NLO crystals, especially for the DUV pyro-borates. Herein, we will describe the synthesis, experimental and computational characterization as well as the functional properties of the new DUV NLO material, Ba₄Ca(B₂O₅)₂F₂.A polycrystalline sample of Ba₄Ca(B₂O₅)₂F₂ was synthesized by the conventional solid-state reaction and the purity was confirmed by powder X-ray diffraction (XRD) (Fig. S1^†). With the polycrystalline sample, the thermal behavior of Ba₄Ca(B₂O₅)₂F₂ was studied by the thermogravimetric (TG) and differential scanning calorimetry (DSC) measurements. The heating DSC curve shows a sharp endothermic peak at 815 °C with no obvious weight loss in the TG curve (Fig. S2^†), suggesting that Ba₄Ca(B₂O₅)₂F₂ has good thermal stability. To further investigate the thermal behavior of Ba₄Ca(B₂O₅)₂F₂, the polycrystalline sample was calcined at 840 °C and the XRD analysis showed that the calcined sample was Ba₄Ca(B₂O₅)₂F₂, Ba₂Ca(BO₃)₂ (PDF #01-085-2268), Ba₂CaB₆O₁₂ (PDF #01-075-1401) and other unknown phases (Fig. S3^†). These results illustrate that Ba₄Ca(B₂O₅)₂F₂ melts incongruently and the suitable flux is necessary for the crystal growth.With the Na₂O–PbF₂–B₂O₃ as the flux, millimeter-sized block crystals of Ba₄Ca(B₂O₅)₂F₂ were grown for the single-crystal XRD structure determination. Ba₄Ca(B₂O₅)₂F₂ crystallizes in the NCS and polar space group, P2₁ (Table S1^†). In the asymmetric unit, there are four unique Ba, one Ca, four B, ten O, and two F atom(s), which all fully occupy the 2a Wyckoff positions (Table S2^†). All B atoms are coordinated to three oxygen atoms to form the BO₃ triangles with the B–O distances ranging from 1.312(17) to 1.460(16) Å and O–B–O angles varying from 108.0(13) to 130.2(15)°. The BO₃ triangles are further connected to form two types of B₂O₅ dimers, i.e. plane B(1,3)₂O₅ and twisted B(2,4)₂O₅, which are the BBUs of Ba₄Ca(B₂O₅)₂F₂. The Ca atoms are coordinated to six oxygen atoms to form CaO₆ octahedra with the Ca–O distances ranging from 2.285(9) to 2.325(13) Å. For the Ba²⁺ cations, they exhibit three different coordination environments, Ba(1,2)O₆F₂, Ba(3)O₈F₂, and Ba(4)O₇F₂ (Fig. S4^†) with the Ba–O distances ranging from 2.585(9) to 3.250(11) Å and the Ba–F bond lengths ranging from 2.635(8) to 2.736(8) Å. Remarkably, for the F⁻ anions, each unique fluorine atom serves as a common vertex for four Ba atoms to form the FBa₄ polyhedra (Fig. S5a^†), which could be treated as fluorine-centered secondary building units (SBUs). The Ba–F–Ba angles vary from 99.0 (2) to 120.2 (3)°. The bond valence sum (BVS) calculations show the values of 1.67–1.97, 2.45, 2.88–3.10, 1.78–2.13, and 0.95–1.09, for Ba²⁺, Ca²⁺ B³⁺, O²⁻, and F⁻, respectively (Table S2^†). The BVSs of atoms are consistent with their expected oxidation states except the one from the Ca²⁺ cations. The larger BVSs of Ca²⁺ cations can be attributed to six shorter Ca–O bond lengths, which are also observed in other Ca²⁺-containing borates, such as YCa₃(VO)₃(BO₃)₄ (2.44),²⁴ Rb₂Ca₃B₁₆O₂₈ (2.29), and Cs₂Ca₃B₁₆O₂₈ (2.30).²⁵The structure of Ba₄Ca(B₂O₅)₂F₂ is shown in Fig. 1. In the structure, the plane B(1,3)₂O₅ dimer is first connected with four CaO₆ octahedra, meanwhile, each CaO₆ octahedron is also linked by four B(1,3)₂O₅ dimers through sharing their four equatorial O atoms to form a unique planar pentagonal [Ca(B₂O₅)]_∞ layer in the b–c plane (Fig. 1a, b). Then, these [Ca(B₂O₅)]_∞ layers are further linked by the twisted B(2,4)₂O₅ dimers to construct a 3D framework with Ba²⁺ cations maintaining the charge balance (Fig. 1c). Remarkably, for the arrangements of the Ba²⁺ cations and the F⁻ anions, the fluorine-centered SBU FBa₄ polyhedra are linked to construct the 2D [F₂Ba₄] infinite layer (Fig. S5b^†) with the same orientation, which further fills the apertures in the [Ca(B₂O₅)₂] framework (Fig. S5c^†). The existence of fluorine-centered SBUs would certainly have a strong influence on the local coordinate environments, and finally on the whole structure.²⁶Open in a separate windowFig. 1(a) The [Ca(B₂O₅)] layer is composed of B₂O₅ dimers and CaO₆ octahedra. (b) The planar pentagonal topology layer. The comparison of structures between (c) Ba₄Ca(B₂O₅)₂F₂ and (d) KBBF.It is very interesting that Ba₄Ca(B₂O₅)₂F₂ contains a planar pentagonal [Ca(B₂O₅)]_∞ layer, which is similar to the [Be₂BO₃F₂]_∞ layer in KBBF. The structural evolution from KBBF to Ba₄Ca(B₂O₅)₂F₂ is also shown in Fig. 1c and d. In KBBF, the BBUs are the planar BO₃ triangles, which are connected with BeO₃F in the a–b plane by strong covalent bonds to form the [Be₂BO₃F₂]_∞ layers (Fig. S6c^†) and the [Be₂BO₃F₂]_∞ layers have achieved excellent NLO properties of the KBBF crystal.⁷ However in Ba₄Ca(B₂O₅)₂F₂, the BO₃ triangles are changed into the B₂O₅ dimers, and the BeO₃F tetrahedra are substituted by the CaO₆ polyhedra. These B₂O₅ dimers are also connected by the CaO₆ polyhedra to form the interesting planar pentagonal [Ca(B₂O₅)]_∞ layer (Fig. S6d^†). More importantly, in KBBF, the adjacent [Be₂BO₃F₂]_∞ layers are connected by the weak K⁺-F⁻ ionic bonds that results in the strong layer habit of the KBBF crystals, whereas in Ba₄Ca(B₂O₅)₂F₂, the [Ca(B₂O₅)]_∞ layers are bridged by the strong covalent B–O bonds to form a stable 3D framework, which will greatly overcome the layering tendency of the KBBF crystal and facilitate the crystal growth.In addition, we also notice that the planar pentagonal [Ca(B₂O₅)]_∞ layer maybe helpful for enhancing the SHG responses of pyro-borates because small SHG responses of pyro-borates are attributed to the typical twisted configurations of the B₂O₅ groups, which are unfavorable for forming the π-conjugation and the superposition of the microscopic SHG response. For example, α-Li₄B₂O₅, a DUV transparent pyro-borate with sole B₂O₅ units as the BBUs, has a weak SHG response, which may be derived from the twisted B₂O₅ groups and non-planar arrangements (Fig. S7a^†). However, in Ba₄Ca(B₂O₅)₂F₂, the planar configuration of the pentagonal layers can assist the B₂O₅ groups to adopt a nearly coplanar arrangement (Fig. S7b^†) and effectively enhance the π-conjugation of B₂O₅ groups. The better π-conjugation of the planar B₂O₅ groups in the planar pentagonal [Ca(B₂O₅)]_∞ layer has also been confirmed by the electron orbital calculation based on the first-principles calculations.²⁷ The calculated result is shown in Fig. 2. Clearly, the prominent conjugated interactions are observed in the nearly coplanar B(1,3)₂O₅ dimers of Ba₄Ca(B₂O₅)₂F₂ (Fig. 2a), whereas it does little in the twisted B(2,4)₂O₅ dimers of Ba₄Ca(B₂O₅)₂F₂ (Fig. 2b) and two types of twisted B₂O₅ dimers in α-Li₄B₂O₅ (Fig. 2c and d). It can be expected that the nearly coplanar B₂O₅ dimers are more conducive to the large SHG response than the twisted B₂O₅ dimers. Remarkably, the similar pentagonal layers are also observed in other pyro-phosphates, such as Ba₂NaClP₂O₇, K₂Sb(P₂O₇)F, Rb₃PbBi(P₂O₇)₂, and Rb₃BaBi(P₂O₇)₂. Clearly, as pyro-phosphates are the non-π-conjugated systems, the planar pentagonal layers are only helpful for the orientation of anion groups.^28–31 However, they cannot form the better π-conjugation. Therefore, the better π-conjugation of the nearly coplanar B₂O₅ groups in planar pentagonal layers of pyro-borate Ba₄Ca(B₂O₅)₂F₂ would have a different contributing mechanism to the SHG effect with other non-π-conjugated pyro-phosphates.Open in a separate windowFig. 2The orbitals of the nearly coplanar B(1,3)₂O₅ (a) and twisted B(2,4)₂O₅ dimers (b) in Ba₄Ca(B₂O₅)₂F₂. The orbitals of two twisted B₂O₅ dimers (c and d) in α-Li₄B₂O₅.The presence of BO₃ triangles in Ba₄Ca(B₂O₅)₂F₂ is confirmed by the IR spectral measurements (Fig. S8^†). The peaks at 1362 cm⁻¹ and 1208 cm⁻¹ can be attributed to the asymmetric stretching of BO₃ groups.³² A strong band at 1069 cm⁻¹ in the IR spectrum may be associated with the stretching vibration of B–O–B in B₂O₅.^33,34 The weak absorption bands at 950, and 810 cm⁻¹ correspond to the symmetrical stretching vibrations of BO₃ and B–O–B in B₂O₅, respectively. The peaks at 751 and 615 cm⁻¹ can be attributed to the out-of-plane bending of the BO₃ groups.³⁴ Further, the UV-vis-NIR diffuse reflectance spectrum was also measured (Fig. S9^†), which shows that Ba₄Ca(B₂O₅)₂F₂ is transparent down to the DUV region with a UV cut-off edge less than 190 nm (corresponding to a large band gap of 6.2 eV), which is comparable to the newly developed NLO-active borates, such as RbB₃O₄F₂ (<190 nm), CsZn₂BO₃X₂ (X₂ = F₂,Cl₂, and FCl)) (<190 nm) and so on.^35–38 The short cut-off edge demonstrates the potential application of Ba₄Ca(B₂O₅)₂F₂ as a DUV NLO crystal.As Ba₄Ca(B₂O₅)₂F₂ crystalizes in the NCS space group P2₁, it possesses the SHG response, which was measured by the Kurtz-Perry method with the well-known NLO material KH₂PO₄ (KDP) as a reference.³⁹ As shown in Fig. 3, the SHG intensities of Ba₄Ca(B₂O₅)₂F₂ increase with the increase of particle sizes, indicating that Ba₄Ca(B₂O₅)₂F₂ is type-I phase-matchable. The SHG intensity of Ba₄Ca(B₂O₅)₂F₂ at the particle size of 150–212 μm is about 2.2 times that of KDP, and is larger than that of KBBF (1.2 × KDP) or comparable with those newly reported UV NLO crystals, i.e. γ-Be₂BO₃F (2.3 × KDP),⁶ β-Rb₂Al₂B₂O₇ (2 × KDP),⁴⁰ Li₄Sr(BO₃)₂ (2 × KDP),⁴¹ CsB₄O₆F(∼1.9 × KDP).² In addition, as we know, the SHG response of Ba₄Ca(B₂O₅)₂F₂ is the largest among all the known DUV transparent borates with B₂O₅ units (Table S4^†). Its SHG response (2.2 × KDP) is about seven times larger than that of α-Li₄B₂O₅ (0.3 × KDP), another DUV transparent pyro-borate with sole B₂O₅ units.Open in a separate windowFig. 3(a) Phase-matching curve, i.e., particle size vs. SHG intensity, data for Ba₄Ca(B₂O₅)₂F₂ and KH₂PO₄ (KDP) as reference. The solid curve is a guide for the eye, not a fit to the data. (b) Oscilloscope traces showing SHG intensities for Ba₄Ca(B₂O₅)₂F₂ and KDP.To understand the origin of the excellent optical properties of Ba₄Ca(B₂O₅)₂F₂, we also carried out the first-principles calculations.²⁷ It shows that Ba₄Ca(B₂O₅)₂F₂ has an indirect band gap of 6.34 eV (Figures S10a^†), which is in accordance with the experimental results. The valence band maximum (VBM) of Ba₄Ca(B₂O₅)₂F₂ is mainly composed of the orbitals in Ba, and O atoms, while the conduction band minimum (CBM) is dominantly composed of the orbitals in Ba, B, and O atoms. Therefore, the band gap of Ba₄Ca(B₂O₅)₂F₂ is mainly determined by Ba atoms and B₂O₅ groups. Based on the calculated electron structure, the NLO coefficients of Ba₄Ca(B₂O₅)₂F₂ are also calculated. The largest NLO coefficient of Ba₄Ca(B₂O₅)₂F₂ is d₂₂ = −0.524 pm V⁻¹, which is about 5 times lower than that of α-Li₄B₂O₅ (d₂₄ = −0.102 pm V⁻¹) (Table S5a^†), which is matched with the experimental one. Further, the SHG-weighted density maps of Ba₄Ca(B₂O₅)₂F₂ are shown in Fig. 4. These reveal that B₂O₅ dimers make the dominant contribution (72.7%) to the total SHG effect (Table S5b^†). The band-resolved SHG analysis can also conclude that B–O orbitals in Ba₄Ca(B₂O₅)₂F₂ contribute more to the SHG response than those in α-Li₄B₂O₅ (Fig. S10b, S10c^†), indicating that the arrangements of B₂O₅ dimers in Ba₄Ca(B₂O₅)₂F₂ is more beneficial for the large SHG response. And different from α-Li₄B₂O₅, F-centered secondary building units (SBUs) exist in the structure of Ba₄Ca(B₂O₅)₂F₂, and they are further linked to construct 2D [F₂Ba₄]_∞ infinite layers, which could help B₂O₅ groups arrange in a planar pattern (Fig. S5^†).²⁶ So, based on the above analysis, we can conclude that the nearly coplanar B₂O₅ dimers in the planar pentagonal layer and the SBU FBa₄ tetrahedra make a significant contribution to the SHG response of Ba₄Ca(B₂O₅)₂F₂.Open in a separate windowFig. 4The SHG-weighted density maps of the virtual electron process (a) and virtual hole process (b) of d₂₂ for Ba₄Ca(B₂O₅)₂F₂.     

Heterodoped nanoflakes: synthesis and characterization of sulfur‐doped NbSe2 nanoflakes

Doping of NbSe₂ with heteroatoms is an effective way to tailor its properties. Here, solid phase synthesis process has been utilized for growing uniform and excellent crystalline nano‐NbSe₂ by sulfur dopant during the growing process. The sulfur‐doped mechanism of nano‐NbS_2xSe_2(1‐x)(x = 0.03∼0.2) has been investigated: the sulfur atoms not only replace the Se position but also intercalate in layer gap by one‐step reaction. In the structure of NbSe₂, the sulfur atoms replace the positions of Se atoms and then are located in the empty octahedral positions of van der waals gap between the NbSe₂ layers with the increase of sulfur content. The lubrication properties of the as‐prepared NbSe₂ and sulfur‐doped NbSe₂ powders as additives in HVI1500 base oil were discussed. The lubrication properties of base oil was improved by both NbSe₂ and sulfur‐doped NbSe₂. Furthermore, the lubrication properties of sulfur‐doped (0.1at%) NbSe₂ are better than those of pure NbSe₂ in HVI1500 base oil, which could be attributed to their thin laminated structure and the sulfur dopant.     

Solvation and solvatochromism in CO2-expanded liquids. 1. Simulations of the solvent systems CO2 + cyclohexane, acetonitrile, and methanol

Molecular dynamics simulations of CO(2)-expanded cyclohexane, acetonitrile, and methanol are reported at various compositions along the experimental bubble-point curve at 298 K. Simulated properties include energies, local compositions, viscosities, diffusion coefficients, and dielectric constants and relaxation times. On the basis of the limited comparisons to experimental data currently available, the results indicate that simple intermolecular potential models previously developed for simulating the pure components provide reasonable representations of the energetics and dynamics of these gas-expanded liquids.     

Arrangement, conformation, and mobility of surfactant molecules intercalated in montmorillonite prepared at different pillaring reagent concentrations as studied by solid-state NMR spectroscopy

The arrangement, conformation, and mobility of dodecyltrimethylammonium cations (DDTMA+) intercalated in montmorillonite prepared with different pillaring reagent concentrations have been studied by 13C relaxation time measurement, cross-polarization dynamics, and two-dimensional proton wide-line separation (2D WISE) spectroscopy, as well as X-ray powder diffraction (XRD). We demonstrate that the arrangement of DDTMA+ and the mobility of various groups are different, depending on the pillaring concentration, but the conformations of alkyl chains are similar. XRD experiments illustrate that at three different pillaring concentrations (DDmt0.2, DDmt0.5, and DDmt1.0), the organic cations adopt a lateral-monolayer, lateral-monolayer, and pseudotrilayer arrangement, respectively. 13C MAS NMR reveals that the alkyl chains at the three concentrations uniformly display a large amount of mixed trans and gauch conformation (disordered) and a small amount of trans conformation (ordered). 13C spin-lattice relaxation time and 1H-13C cross-polarization dynamics measurement, along with 2D WISE NMR experiments, indicate that the mobility is much different for various groups at a given concentration and for a given group at different concentrations. At each concentration N-methyl unusually possesses the highest mobility, even exceeding that of the terminal methyl; at different concentrations the N-methyl and terminal methyl in DDmt1.0 exhibit the highest mobility compared with the other two samples.     

Cationic zinc enolates as highly active catalysts for acrylate polymerization

Unprecedented cationic zinc enolates have been generated by a novel activation route involving the amido to imino ligand transformation with B(C6F5)3, structurally characterized, and utilized as highly active catalysts for the production of high molecular weight polyacrylates at ambient temperature.     

Some relations on the ordering of trees by minimal energies between subclasses of trees

The energy of a graph is defined as the sum of the absolute values of all eigenvalues of the graph. A tree is said to be non-starlike if it has at least two vertices with degree more than 2. A caterpillar is a tree in which a removal of all pendent vertices makes a path. Let $\mathcal{T}_{n,d}$ , $\mathbb{T}_{n,p}$ be the set of all trees of order n with diameter d, p pendent vertices respectively. In this paper, we investigate the relations on the ordering of trees and non-starlike trees by minimal energies between $\mathcal{T}_{n,d}$ and $\mathbb{T}_{n,n-d+1}$ . We first show that the first two trees (non-starlike trees, resp.) with minimal energies in $\mathcal{T}_{n,d}$ and $\mathbb{T}_{n,n-d+1}$ are the same for 3≤d≤n?2 (3≤d≤n?3, resp.). Then we obtain that the trees with third-minimal energy in $\mathcal{T}_{n,d}$ and $\mathbb{T}_{n,n-d+1}$ are the same when n≥11, 3≤d≤n?2 and d≠8; and the tree with third-minimal energy in $\mathcal{T}_{n,8}$ is the caterpillar with third-minimal energy in $\mathbb{T}_{n,n-7}$ for n≥11.     

碘酸钾滴定法测定ITO粉末材料中的锡

建立了以锌粉-氢氧化钠熔融样品,盐酸浸取,用盖氏漏斗作为还原装置,铁粉和铝粒将锡还原,碘酸钾滴定法测定ITO粉末材料中锡的分析方法。方法测定结果稳定,精密度好,相对标准偏差为0.42%~0.67%,加标回收率在99.8%~101%,能够满足ITO粉末中锡的测定要求。     

Surface Plasmon Resonance‐based Inhibitive Immunoassay Coupled with Dummy Template Molecularly Imprinted Polymer Solid Phase Extraction for On‐line Analysis of Trace Clenbuterol

A new indirect inhibitive immunoassay using surface plasmon resonance (SPR) coupled with molecularly imprinted polymer (MIP) was developed and applied for the analysis of trace clenbuterol (CL). A MIP coating using phenylephrine as the dummy template was synthesized in a flexible quartz capillary (30 cm×0.25 mm i.d.) by in situ polymerization technique, which then was used as the online solid phase extraction (SPE) tube before SPR detection. The thickness of the coating was 198 nm on average, illustrated by scanning electron microscope (SEM) image. The mechanism for adsorption of CL on dummy template MIP was found to be a Freundlich isotherm and pseudo‐second‐order model. The immunoassay was conducted on BIAcore 3000 biosensor automatically without pre‐treatment. The calibration curve was generated by linear fit in the range of 0.1–10 ng L^‐1 and 10–100 ng L^‐1. The detection limit was 0.1 ng L^–1, which is super sensitive. This method was directly applied for the analysis of real‐world samples without pretreatment.     

C4 Cumulene and the Corresponding Air‐Stable Radical Cation and Dication

A neutral C₄ cumulene 1 that includes a cyclic alkyl(amino) carbene (cAAC), its air‐stable radical cation 1 ^.+, and dication 1 ²⁺ have been synthesized. The redox property of 1 ^.+ was studied by cyclic voltammetry. EPR and theoretical calculations show that the unpaired electron in 1 ^.+ is mainly delocalized over the central C₄ backbone. The commercially available CBr₄ is utilized as a source of dicarbon in the cumulene synthesis.