Photodissociation of dimethylnitrosamine

Photodissociation of (CH₃)₂N-NO following S₁(nπ^*) ← S₀ excitation yields (CH₃)₂N^? and NO with a quantum yield of 1.03 ± 0.10. These fragments recombine leaving no stable photopioducts. A fraction of NO produced by photolysis is vibrationally excited. The rate of the NO(v = 1) relaxation in collision with (CH₃)₂N-NO, measured by IR fluorescence, is (1.47 ± 0.03) × 10⁴ s^?1 Torr^?1.     

“Anti-electrostatic” halogen bonding in solution

Halogen-bonded (XB) complexes between halide anions and a cyclopropenylium-based anionic XB donor were characterized in solution for the first time. Spontaneous formation of such complexes confirms that halogen bonding is sufficiently strong to overcome electrostatic repulsion between two anions. The formation constants of such “anti-electrostatic” associations are comparable to those formed by halides with neutral halogenated electrophiles. However, while the latter usually show charge-transfer absorption bands, the UV-Vis spectra of the anion–anion complexes examined herein are determined by the electronic excitations within the XB donor. The identification of XB anion–anion complexes substantially extends the range of the feasible XB systems, and it provides vital information for the discussion of the nature of this interaction.

Spontaneous formation of “anti-electrostatic” complexes in solution demonstrates that halogen bonding can be sufficiently strong to overcome anion–anion repulsion when the latter is attenuated by the polar medium.

Halogen bonding (XB) is an attractive interaction between a Lewis base (LB) and a halogenated compound, exhibiting an electrophilic region on the halogen atom.¹ It is most commonly related to electrostatic interaction between an electron-rich species (XB acceptor) and an area of positive electrostatic potential (σ-holes) on the surface of the halogen substituent in the electrophilic molecule (XB donor).² Provided that mutual polarization of the interacting species is taken into account, the σ-hole model explains geometric features and the variation of stabilities of XB associations, especially in the series of relatively weak complexes.³ Based on the definition of halogen bonding and its electrostatic interpretation, this interaction is expected to involve either cationic or neutral XB donors. Electrostatic interaction of anionic halogenated species with electron-rich XB acceptors, however, seems to be repulsive, especially if the latter are also anionic. Yet, computational analyses predicted that halogen bonding between ions of like charges, called “anti-electrostatic” halogen bonding (AEXB),⁴ can possibly be formed^5–12 and the first examples of AEXB complexes formed by different anions, i.e. halide anions and the anionic iodinated bis(dicyanomethylene)cyclopropanide derivatives 1 (see Scheme 1) or the anionic tetraiodo-p-benzoquinone radical, were characterized recently in the solid state.^13,14 The identification of such complexes substantially extends the range of feasible XB systems, and it provides vital information for the discussion of the nature of this interaction. Computational results, however, significantly depend on the used methods and applied media (gas phase vs. polar environment and solvation models) and the solid state arrangements of the XB species might be affected by crystal forces and/or counterions. Unambiguous confirmation of the stability of the halogen-bonded anion–anion complexes and verification of their thermodynamic characteristics thus requires experimental characterization of the spontaneous formation of such associations in solution. Still, while the solution-phase complexes formed by hydrogen bonding between two anionic species were reported previously,^15–17 there is currently no example of “anti-electrostatic” XB in solution.Open in a separate windowScheme 1Structures of the XB donor 1 and its hydrogen-substituted analogue 2.To examine halogen bonding between two anions in solution, we turn to the interaction between halides and 1,2-bis(dicyanomethylene)-3-iodo-cyclopropanide 1 (Scheme 1).^‡ Even though this compound features a cationic cyclopropenylium core, it is overall anionic, and calculations have demonstrated that its electrostatic potential is universally negative across its entire surface.¹³ The solution of 1 (with tris(dimethylamino)cyclopropenium (TDA) as counterion) in acetonitrile is characterized by an absorption band at 288 nm with ε = 2.3 × 10⁴ M⁻¹ cm⁻¹ (Fig. 1). As LB, we first applied iodide anions taken as a salt with n-tetrabutylammonium counter-ion, Bu₄NI. This salt does not show absorption bands above 290 nm, but its addition to a solution of 1 led to a rise of absorption in the 290–350 nm range (Fig. 1). Subtraction of the absorption of the individual components from that of their mixture produced a differential spectrum which shows a maximum at about 301 nm (insert in Fig. 1). At constant concentration of the XB donor (1) and constant ionic strength, the intensity of the absorption in the range of 280–300 nm (and hence differential absorbance, ΔAbs) rises with increasing iodide concentration (Fig. S1 in the ESI^†). This suggests that the interaction of iodide with 1 results in the formation of the [1, I⁻]-complex which shows a higher absorptivity in this spectral range (eqn (1)):1 + X⁻ ⇌ [1, X⁻]1Open in a separate windowFig. 1Spectra of acetonitrile solutions with constant concentration of 1 (0.60 mM) and various concentrations of Bu₄NI (6.0, 13, 32, 49, 75, 115 and 250 mM, solid lines from the bottom to the top). The dashed lines show spectra of the individual solutions 1 (c = 0.60 mM, red line) and Bu₄NI (c = 250 mM, blue line). The ionic strength was maintained using Bu₄NPF₆. Insert: Differential spectra of the solutions obtained by subtraction of the absorption of the individual components from the spectra of their corresponding mixtures.To clarify the mode of interaction between 1 and iodide in the complex, we also performed analogous measurements with the hydrogen-substituted compound 2 (see Scheme 1). The addition of iodide to a solution of 2 in acetonitrile did not increase the absorption in the 280–300 nm spectral range. Instead, some decrease of the absorption band intensity of 2 with the increase of concentration of I⁻ anions was observed (Fig. S2 in the ESI^†). Such changes are related to a blue shift of this band resulting from the hydrogen bonding between 2 and iodide (formation of hydrogen-bonded [2, I⁻] complex is corroborated by the observation of the small shift of the NMR signal of the proton of 2 to the higher ppm values in the presence of I⁻ anions, see Fig. S3 in the ESI^†).^§ Furthermore, since H-compound 2 should be at least as suitable as XB donor 1 to form anion–π complexes with the halide, this finding (as well as solid-state and computational data^¶) rules out that any increase in absorption in this region observed with the I-compound 1 may be due to this alternative interaction.Likewise, the addition of NBu₄I to a solution of TDA cations taken as a salt with Cl⁻ anions did not result in an increase in the relevant region. Hence, we could also rule out anion–π interactions with the TDA counter-ions as source of the observed changes, which is in line with previous reports on the electron-rich nature of TDA.¹⁸All these observations (supported by the computational analysis, vide infra) indicate that the [1, I⁻] complex (eqn (1)) is formed via halogen bonding of I⁻ with iodine substituents in 1. The changes in the intensities of the differential absorption ΔAbs as a function of the iodide concentration (with constant concentration of XB donor (1) as well as constant ionic strength) are well-modelled by the 1 : 1 binding isotherm (Fig. S1 in the ESI^†). The fit of the absorption data produced a formation constant of K = 15 M⁻¹ for the [1, I⁻] complex (Table 1).^|| The overlap with the absorption of the individual XB donor hindered the accurate evaluation of the position and intensity of the absorption band of the corresponding complex which is formed upon LB-addition to 1. As such, the values of Δλ_max shown in Table 1 represent a wavelength of the largest difference in the absorptivity of the [1, I⁻] complex and individual anion 1, and Δε reflects the difference of their absorptivity at this point (see the ESI^† for the details of calculations).Equilibrium constants and spectral characteristics of the complexes of 1 with halide anions X⁻

笃斯茎中六种无机元素含量分析

应用原子吸收光谱法测定了内蒙古地产的笃斯茎、叶中的Cu,Fe,Zn,Mn,Ca,Mg等六种人体必需微量元素及宏量元素的含量。从而为评价笃斯的品质及其药理、药效提供了具有一定价值的数据。     

Layered Black Phosphorus: Strongly Anisotropic Magnetic,Electronic, and Electron‐Transfer Properties

Layered elemental materials, such as black phosphorus, exhibit unique properties originating from their highly anisotropic layered structure. The results presented herein demonstrate an anomalous anisotropy for the electrical, magnetic, and electrochemical properties of black phosphorus. It is shown that heterogeneous electron transfer from black phosphorus to outer‐ and inner‐sphere molecular probes is highly anisotropic. The electron‐transfer rates differ at the basal and edge planes. These unusual properties were interpreted by means of calculations, manifesting the metallic character of the edge planes as compared to the semiconducting properties of the basal plane. This indicates that black phosphorus belongs to a group of materials known as topological insulators. Consequently, these effects render the magnetic properties highly anisotropic, as both diamagnetic and paramagnetic behavior can be observed depending on the orientation in the magnetic field.     

Synergy between thermal analysis and simulation

Available databases presently used by commercial simulation software packages for the aluminum casting industry are usually armed with material properties for only a few selected standard alloys. In the case of other alloys with different chemical compositions and refinement or modification treatment, thermal analysis could be an invaluable tool to gain necessary properties. The aim of this article is to demonstrate the potential application of the cooling curve analysis in the existing simulation software by improving its accuracy.     

异喹啉酰肼构筑锌配合物的合成、晶体结构及其性质

采用普通溶液法合成了配合物[Zn(eiqnthz)_2]·DMF(1)和[Zn3(piqnthz)_2Cl_2]·2H_2O(2)(Heiqnthz=N,N′-乙酰异喹啉甲酰肼,H2piqnthz=N,N′-丙酰异喹啉甲酰肼)。通过X射线单晶衍射分析、X射线粉末衍射分析、红外光谱分析、热重分析以及荧光光谱分析等分析方法对2个配合物进行结构测定和性质表征。结构分析表明配合物1是单核结构,单斜晶系,空间群为C2/c,锌离子周围有4个氮原子和2个氧原子与之配位,形成一个畸变的N4O2八面体构型。配合物2属于单斜晶系,C2/c空间群,三核结构。中心原子Zn(1)、Zn(2)、Zn(3)均为5配位,Zn(1)、Zn(3)位于分子两端并且是变形四角锥配位构型,Zn(2)位于中间形成三角双锥配位构型,整体呈V字型。荧光分析表明Heiqnthz、H2piqnthz与锌(Ⅱ)离子配位后其荧光都发生较大的红移。     

Toluene as a novel carrier of xanthates—preparation,use and surrogate of S-tri- and di-chloromethyl xanthates

Toluene has been identified as a novel carrier of xanthates. Their corresponding fragmentative precursors proved to behave efficiently in radical group transfer reactions. As examples, unprecedented S-tri/di-chloromethyl xanthates could be prepared, isolated and further used in radical additions to olefins. Their precursors (de-aromatized toluene upon which is grafted, at one end, a tri/di-chloromethyl-group and, at the other end, a dithiocarbonyl group) can also be used directly in the transfer of both groups to olefins. The re-aromatizing loss of toluene by radical initiated fragmentation of the precursors brings thus new opportunities to the chemistry of xanthates, exemplified here in the intermolecular additions to olefins of new S-tri/di-chloromethyl xanthates.