Observation of the Q(3/2) Λ-doublet transitions for X2Π3/2 OD in helium nanodroplets

The deuteroxyl radical (OD) has been isolated in superfluid helium nanodroplets and characterised by infrared depletion spectroscopy. Two resolved Q(3/2) lines are observed, with a separation that is 4.88 (10) times larger than in the gas phase. This is similar to that previously reported for He-solvated OH (5.30 (2)), for which it was shown that the splitting could be reproduced by a model that assumes a small parity dependence of the rotor's effective moment of inertia [P.L. Raston, T. Liang, and G.E. Douberly, J. Phys. Chem. A (2013). DOI:10.1021/jp312335q]. With this model, the OD Λ-doublet splitting in liquid He is reproduced with B^e and B^f rotational constants that differ by ≈0.24%.     

Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism

A newly synthesized one‐dimensional (1D) hydrogen‐bonded (H‐bonded) rhodium(II)–η⁵‐semiquinone complex, [Cp*Rh(η⁵‐p‐HSQ‐Me₄)]PF₆ ([ 1 ]PF₆; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric–antiferroelectric second‐order phase transition at 237.1 K. Neutron and X‐ray crystal structure analyses reveal that the H‐bonded proton is disordered over two sites in the room‐temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF₆^? ion. The relative permittivity ε_b′ along the H‐bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of ¹³C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low‐temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10^?4–10^?6 s in the temperature range of 240–270 K. DFT calculations predict that the protonation/deprotonation of [ 1 ]⁺ leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π‐bonded rhodium fragment, producing the stable η⁶‐hydroquinone complex, [Cp*Rh³⁺(η⁶‐p‐H₂Q‐Me₄)]²⁺ ([ 2 ]²⁺), and η⁴‐benzoquinone complex, [Cp*Rh⁺(η⁴‐p‐BQ‐Me₄)] ([ 3 ]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [ 2 ]²⁺ and [ 3 ], which would be generated in the H‐bonded chain.     

Raman-in-SEM,a multimodal and multiscale analytical tool: Performance for materials and expertise

The availability of Raman spectroscopy in a powerful analytical scanning electron microscope (SEM) allows morphological, elemental, chemical, physical and electronic analysis without moving the sample between instruments. This paper documents the metrological performance of the SEMSCA commercial Raman interface operated in a low vacuum SEM. It provides multiscale and multimodal analyses as Raman/EDS, Raman/cathodoluminescence or Raman/STEM (STEM: scanning transmission electron microscopy) as well as Raman spectroscopy on nanomaterials. Since Raman spectroscopy in a SEM can be influenced by several SEM-related phenomena, this paper firstly presents a comparison of this new tool with a conventional micro-Raman spectrometer. Then, some possible artefacts are documented, which are due to the impact of electron beam-induced contamination or cathodoluminescence contribution to the Raman spectra, especially with geological samples. These effects are easily overcome by changing or adapting the Raman spectrometer and the SEM settings and methodology. The deletion of the adverse effect of cathodoluminescence is solved by using a SEM beam shutter during Raman acquisition. In contrast, this interface provides the ability to record the cathodoluminescence (CL) spectrum of a phase. In a second part, this study highlights the interest and efficiency of the coupling in characterizing micrometric phases at the same point. This multimodal approach is illustrated with various issues encountered in geosciences.     

Structure of Zinc and Nickel Histidine Complexes in Solution Revealed by Molecular Dynamics and Raman Optical Activity

The histidine residue has an exceptional affinity for metals, but solution structure of its complexes are difficult to study. For zinc and nickel complexes, Raman and Raman optical activity (ROA) spectroscopy methods to investigate the link between spectral shapes and the geometry were used. The spectra were recorded and interpreted on the basis of ionic equilibria, molecular dynamics, ab initio molecular dynamics, and density functional theory. For zwitterionic histidine the dominant tautomer was determined by the decomposition of experimental spectra into calculated subspectra. An octahedral structure was found to prevail for the ZnHis₂ complex in solution, in contrast to a tetrahedral arrangement in the crystal phase. The solution geometry of NiHis₂ is more similar to the octahedral structure found by X-ray. The Raman and ROA structural determinations of metal complexes are dependent on extensive computations, but reveal unique information about the studied systems.     

The use of different dispersive Raman spectrometers for the analysis of uranium compounds

The performances of three different Raman spectrometers were compared and evaluated as a suitable tool for the analysis of a range of uranium compounds with a view to application in nuclear forensics. These included uranium ore concentrates of different chemical composition and uranium dioxide in the form of powder and sintered fuel pellet. The three spectrometers are termed as ‘portable’ or ‘hand-held’ from Ahura Scientific (785 nm), ‘Senterra’ from Bruker (532 and 785 nm), ‘T64000′ from HORIBA Jobin Yvon (488.0, 514.5, 647.1 and 752.5 nm). Figures of merit such as sensitivity, signal-to-noise ratio and detection capability were compared. The portable Raman displayed fairly good sensitivity and process related impurities could be detected despite the miniaturisation but it was unable to measure darkly coloured powders such as calcined ore concentrates or uranium dioxide powder. The bench-top spectrometer Senterra had the best sensitivity for all the seven measured uranium compounds and the best signal-to-noise ratio for six of the compounds. Laboratory T64000 had the best resolution and at the same time resulting in the poorest sensitivity among the three spectrometers for all compounds measured. However, T64000 has very low level of noise therefore leading to better signal-to-noise that were comparable, if not better than the portable or Senterra. All industrial compounds measured in this study could not be measured with higher frequency laser thus impeding the observation of N–H or O–H vibration bands, of which the latter could be observed with laboratory synthesized material.     

Selective Benzylic CH-Borylations by Tandem Cobalt Catalysis

Metal-catalyzed C?H activations are environmentally and economically attractive synthetic strategies for the construction of functional molecules as they obviate the need for pre-functionalized substrates and minimize waste generation. Great challenges reside in the control of selectivities, the utilization of unbiased hydrocarbons, and the operation of atom-economical dehydrocoupling mechanisms. An especially mild borylation of benzylic CH bonds was developed with the ligand-free pre-catalyst Co[N(SiMe₃)₂]₂ and the bench-stable and inexpensive borylation reagent B₂pin₂ that produces H₂ as the only by-product. A full set of kinetic, spectroscopic, and preparative mechanistic studies are indicative of a tandem catalysis mechanism of CH-borylation and dehydrocoupling via molecular Co^I catalysts.     

温度对低共熔溶剂影响的二维拉曼光谱研究

低共熔溶剂（DES）作为一种新式的绿色溶剂，在多种化学过程中表现出色，因此在诸多热门范畴都展现出良好的发展潜力。对DES的光谱分析通常局限在一维光谱技术上，但其分辨率低、谱峰重叠严重等缺点，导致光谱数据存在误差。运用二维拉曼光谱（2D Raman），能够明显提高光谱分辨率，并发现重叠峰位置，获得在外扰条件下不同谱峰的变化顺序及其相互作用等重要信息，以实现对复杂体系的精确分析。以氯化胆碱（ChCl）和ZnCl₂合成的DES为例，利用显微共焦激光拉曼光谱仪分别对ChCl和DES进行拉曼实验，发现与ChCl相比，DES中各处峰的整体强度显著下降，原有的谱峰未消失，说明Zn2+的加入没有破坏ChCl的骨架结构。287 cm-1处出现一个新的特征峰，推测有Zn-Cl配位键的伸缩振动。对DES进行升温拉曼实验，发现随着温度的升高，NC₄的不对称伸缩振动峰强度逐渐减小，峰宽变大，峰形变缓，Zn-Cl配位键伸缩振动峰强度逐渐降低，峰位置基本不变，峰形有明显重叠。运用2D Raman技术对溶液内NC₄和Zn-Cl特征峰的变化进行研究，结果表明，随着温度的升高，溶液中发生ChCl向Ch+的解离过程，Zn2+与Cl-形成了多种配合物，ZnCl-₃，Zn₂Cl-₅，Zn₃Cl-₇之间存在相互转化。不同位置的特征峰随温度的变化顺序不同，将特征峰与团簇进行一一归属，得出了各个团簇对温度的敏感程度。基于量子化学中的密度泛函理论，对推测的物质结构进行构型优化和参数计算，证实了其存在的可能性，同时也验证了2D Raman的分析结果准确可行。这些结果将为DES的后续研究提供理论参考，拓展了二维光谱技术的应用范围。     

Near-IR absorbing donor–acceptor charge-transfer gallium complex,an example from non-transition metal chemistry

Gallium(III) catecholates with bipyridine ligand [(3,5-Cat)Ga(bipy)2]I and (3,6-Cat)GaI(bipy) (Cat is di-tert-butylcatecholate) were synthesized and characterized by single-crystal X-ray diffraction. The appearance of near-infrared ligand-to-ligand charge transfer for pentacoordinate complex was observed.