Spectroscopic observation and structure of CS2 dimer

Infrared spectra of the CS(2) dimer are observed in the region of the CS(2) ν(3) fundamental band (～1535 cm(-1)) using a tunable diode laser spectrometer. The weakly bound complex is formed in a pulsed supersonic slit-jet expansion of a dilute gas mixture of carbon disulfide in helium. Contrary to the planar slipped-parallel geometry previously observed for (CO(2))(2), (N(2)O)(2), and (OCS)(2), the CS(2) dimer exhibits a cross-shaped structure with D(2d) symmetry. Two bands were observed and analyzed: the fundamental (C-S asymmetric stretch) and a combination involving this mode plus an intermolecular vibration. In both cases, the rotational structure corresponds to a perpendicular (ΔK = ±1) band of a symmetric rotor molecule. The intermolecular center of mass separation (C-C distance) is determined to be 3.539(7) A?. Thanks to symmetry, this is the only parameter required to characterize the structure, if the monomer geometry is assumed to remain unchanged in the dimer. From the band centers of the fundamental and combination band an intermolecular frequency of 10.96 cm(-1) is obtained, which we assign as the torsional bending mode. This constitutes the first high resolution spectroscopic investigation of CS(2) dimer.     

Direct experimental observation of CS2OH.

The first experimental detection of CS(2)OH is reported. CS(2)OH was observed for about one microsecond after its formation, as an intact isolated species in the gas phase. It was generated by electron transfer to the CS(2)OH(+) ion, prepared in the source of a multisector mass spectrometer by suitable ion-molecule reactions. The vertical formation process allowed characterization of CS(2)OH by structural analysis of CS(2)OH(+). Theoretical calculations were performed at the B3LYP/6-311+G(2d,p) and CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(2d,p) levels of theory. The computed structure and stability of CS(2)OH and CS(2)OH(+) as well as the energetics of the involved processes satisfactorily fit with the experimental results.     

Fate of CS2 in viscose process: a chemistry perspective

Cellulose dissolution in the viscose process has been facilitated through derivatization by carbon disulphide (CS₂) at xanthation stage by converting alkali cellulose (AC) to cellulose xanthate (CX). CX formation has been always accompanied with sulphur based byproducts formation as dictated by the mechanism published in earlier study (Gondhalekar et al. (Cellulose 26 3 1595–1604, 2019)). The sulphur byproducts formed during viscose synthesis are sodium sulphide (Na₂S), sodium trithiocarbonate (Na₂CS₃: TTC) and other minor sulphur compounds. These byproducts continue to form during ripening process as dictated by time and temperature coupled with concentration of free caustic and CS₂ present in the system. These byproducts get converted into sodium sulphate (Na₂SO₄), hydrogen sulphide (H₂S), CS₂ and other sulphurous compounds during spinning. Overall, uncontrolled ripening without parametric optimization adversely impacts raw material (RM) consumption and creates sustainability challenges. Overall optimization based on viscose process fundamental insights presented in this study will effectively help in achieving operational excellence by reducing rate of undesired reactions to improve RM specific consumption and will compliment overall sustainability efforts in viscose industry.

     

Solid-state NMR spectroscopic methods in chemistry

Over the last decades, NMR spectroscopy has grown into an indispensable tool for chemical analysis, structure determination, and the study of dynamics in organic, inorganic, and biological systems. It is commonly used for a wide range of applications from the characterization of synthetic products to the study of molecular structures of systems such as catalysts, polymers, and proteins. Although most NMR experiments are performed on liquid-state samples, solid-state NMR is rapidly emerging as a powerful method for the study of solid samples and materials. This Review outlines some of the developments of solid-state NMR spectroscopy, including techniques such as cross-polarization, magic-angle spinning, multiple-pulse sequences, homo- and heteronuclear decoupling and recoupling techniques, multiple-quantum spectroscopy, and dynamic angle spinning, as well as their applications to structure determination. Modern solid-state NMR spectroscopic techniques not only produce spectra with a resolution close to that of liquid-state spectra, but also capitalize on anisotropic interactions, which are often unavailable for liquid samples. With this background, the future of solid-state NMR spectroscopy in chemistry appears to be promising, indeed.     

Electron spin relaxation of N@C60 in CS2 in CS2

We examine the temperature dependence of the electron spin relaxation times of the molecules N@C60 and N@C70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid CS2 solution. The results are inconsistent with the fluctuating zero-field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S> or =1 spins in liquid solution, and is the mechanism postulated in the literature for these systems. Instead, we find an Arrhenius temperature dependence for N@C60 , indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N@C70 molecule, which has a permanent ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time (T2) ever observed for a molecular electron spin, being 0.25 ms at 170 K.     

Mass transport in sub-2-microm high-performance liquid chromatography

Ultra-high pressure liquid chromatography enables increased separation speed and efficiency. The quantitative improvement in efficiency is lower than that predicted by theory, and the reasons are not known. In this work, slow mass transport due to analyte desorption from the stationary phase is discussed as a possible contribution to the lower than expected efficiency. Data in the literature for the reversed phase elution of acetophenone, for which particle size was varied with constant particle composition and mobile phase, were used to test this possibility. The mass transport terms for the three particles sizes (1.7, 3.5 and 5.0 microm) fit well to a model that includes desorption from the stationary phase as a contribution, and this analysis yields an apparent desorption time constant of 2.0(+/-0.2)ms for acetophenone in a reversed-phase separation. The results indicate that it is reasonable to consider slow desorption as a possible contribution to the reduced plate height for sub-2-microm particles.     

CS21B2(1Σ+u)态预离解产物CS的振转布居研究

用一束波长为210.27 nm的激光将CS2分子激发至预离解态1 B2(1 Σ+u),用另一束激光通过激光诱导荧光(LIF)方法检测碎片CS,在250.5～286.5 nm获得了CS碎片A1 Π←X1 Σ+振转分辨的激发谱.通过对光谱强度的分析,获得了CS碎片v″=0～8的振动布居和v″=1,4～8振动态的转动布居.结果发现,碎片CS的振动布居呈双模结构,分别对应于CS2分子1 B2(1 Σ+u)态的两个解离通道,即CS(X1 Σ+,v″=0～9)+S(3PJ)和CS(X1 Σ+, v″=0～1)+S(1 B2).由此得到两个解离通道的分支比S(3PJ): S(1 B2)为5.6±1.2.与前人193 nm处的研究结果相比, 210.27 nm激发更有利于S(3PJ)通道的生成.此外,实验还发现CS的转动布居不满足热平衡分布,为两个Boltzmann分布的合成.     

2-(取代苯亚氨次甲基)吲哚衍生物的质谱研究

报道了由吲哚-2-甲醛和取代苯胺进行亲核加成反应合成了22个2-(取代苯亚氨次甲基)吲哚衍生物,主要对本类化合物的两种质谱特殊裂解过程进行了分析研究。     

Utilization of CS2 as a source of C1 chemistry for the generation of methyldithioformate

Insertion of CS(2) into the Ru-H bond of cis-[(dppe)(2)Ru(H)(2)] takes place to afford the hydride dithioformate complex trans-[(dppe)(2)Ru(H)(SC(S)H)]. The hydride dithioformate complex reacts under very mild conditions with MeX (X = OTf, I) to give the hydride methyldithioformate derivative trans-[(dppe)(2)Ru(H)(SC(SMe)H)][X]. Three different pathways have been found to cleave off the ester moiety from the metal complex. A method to recover the ruthenium starting material upon elimination of the methyldithioformate is presented. This is a novel case of C(1) chemistry using carbon disulfide.     

Mass spectroscopic fragmentation pathways of 1,8-nonadiyne

Cleavage α to triple bonds in straight-chain hydrocabons with only one triple bond is a very minor process. The mass spectrum of 1,8-nonadiyne (mol. wt 120) shows strong peaks at around m/z91, which points to a major fragmentation pathway of cleavage α to triple bonds in straight-chain diynes. This study attempts to explain this paradox. Through-space interaction was indicated through the use of carbon-13 labelling of the terminal carbon atoms in 1,8-nonadiyne, 1,2,8,9-¹³C-1,8-Nonadiyne and 3,7-¹³C-1,8-nonadiyne were prepared to determine which carbon atoms were lost in the process of [M]⁺˙ and [M? 1]⁺ going to m/z91. These two molecules were chosen for ease of synthesis. Low-resolution mass spectra and low-voltage studies determined that a major portion of carbon atoms being lost were from the middle of the carbon chain. This points to a fragmentation pathway that results from through-space interaction of the two terminal triple bonds. It is likely that ionization enhances this through-space interaction of the two triple bonds.     

Activation of CS2 and CS by ML3 complexes

The aim of this study was to determine the best neutral ML3 metal complexes for activating and cleaving the multiple bonds in CS2 and CS. Current experimental results show that, so far, only one bond in CS2 can be cleaved, and that CS can be activated but the bond is not broken. In the work described in this paper, density functional theory calculations have been used to evaluate the effectiveness of different ML3 complexes to activate the C-S bonds in CS2 and CS, with M = Mo, Re, W, and Ta and L = NH2. These calculations show that the combination of Re and Ta in the L3Re/CS2/TaL3 complex would be the most promising system for the cleavage of both C-S bonds of CS2. The reaction to cleave both C-S bonds is predicted to be exothermic by about 700 kJ mol(-1) and to proceed in an almost barrierless fashion. In addition, we are able to rationalize why the breaking of the C-S bond in CS has not been observed experimentally with M = Mo: this reaction is strongly endothermic. There is a subtle interplay between charge transfer and pi back-donation, and it appears that the Mo-C and Mo-S bonds are not strong enough to compensate for the breaking of the C-S bond. Our results suggest that, instead, CS could be cleaved with ReL3 or, even better, with a combination of ReL3 and TaL3. Molecular orbitals and Mulliken charges have been used to help explain these trends and to make predictions about the most promising systems for future experimental exploration.     

Infrared spectrum of the CS2 trimer: observation of a structure with D3 symmetry

Infrared spectra of a carbon disulfide trimer formed in a pulsed supersonic slit-jet expansion are obtained via direct absorption of a tuneable diode laser in the region of the CS(2)ν(3) fundamental (～1535 cm(-1)). This is the first high-resolution spectroscopic observation of (CS(2))(3). Two bands sharing the same lower state are assigned to ((12)C(32)S(2))(3). These correspond to the two infrared active trimer vibrations (a parallel and a perpendicular band) of the constituent CS(2) monomer asymmetric stretches. The weaker perpendicular band is centered at 1524.613 cm(-1), shifted by -10.74 cm(-1) with respect to the free CS(2) monomer. The parallel band is centered at 1545.669 cm(-1), a vibrational shift of +10.31 cm(-1). Transitions with K≠ 3n and those with K = 0, J = odd in the ground state are absent, establishing that this trimer has D(3) symmetry. The two parameters required to define this structure are determined to be 3.811 ? for the C-C bond distance and 61.8° for the angle between a monomer axis and the plane containing the C atoms. In addition, a parallel band arising from trimers with a single (34)S substitution is observed around 1544.46 cm(-1). Together with the recently observed cross-shaped CS(2) dimer, these results indicate a tendency for CS(2) to form highly symmetric clusters.     

Synthesis and spectroscopic observation of dendrimer-encapsulated gold nanoclusters

We report on the observation of the excitation/emission spectrum of a dendrimer-encapsulated gold nanocluster; the synthesis of Au-PAMAM was based on reduction of HAuCl4 x 3 H2O co-dissolved in methanol together with fourth-generation OH-terminated PAMAM.     

Strength of the PtCS2 bond in Pt(PPh3)2(CS2)

The enthalpy of the reaction: Pt(PPh₃)₂(CH₂CH₂)(cryst.) + CS₂(g) → Pt(PPh₃)₂(CS₂)(cryst.) + CH₂CH₂(g) has been determined as ΔH = ? 4.40 ± 2.2 kJ mol^?1 from solution calorimetry, and the bond dissociation energy D(PtCS₂) shown to be slightly greater than D(PtC₂H₄).     

Solution chemistry of cobalt in liquid hydrogen fluoride

Cobalt(II) fluoride dissolves in HF in the presence of excess BF₃ or AsF₅: solid adducts are isolable from these solutions. Insoluble CoF₃ decomposes to cobalt(II) under the same conditions. The CoF^3?₆ is solvolysed by HF except in the presence of excess F^?. Cs₂CoF₆ is soluble in HF but the solutions decompose above 10°C yielding F₂; such solutions are powerful fluorinating agents and convert MnF₃ to MnF^2?₆ and Xe to XeF₂.