Proton magnetic relaxation study of water orientation around I− and Li+

Proton relaxation time measurements are performed for 6m aqueous solutions of⁷LiI and⁶LiI in D₂O containing small amounts of H₂O. The measurements are done at low temperatures and yield maxima of the relaxation rate plotted against 1/T. From the maxima of the relaxation rates, proteon-I^– and proton-Li⁺ distances in the first coordination sphere of the ions are determined, and from the knowledge of the ion-water oxygen distance it is shown that for iodide a somewhat broadened H-bonded configuration is valid and that for Li⁺ the electric dipole orientation deviates from the radial direction. In order to test the reliability of the method a proton-¹²⁷I interaction study is also performed in KI solution in glycerol. The I-H distance obtained is in satisfactory agreement with that found in the aqueous system.     

DySBr und DySI – Synthese,Kristallstruktur und Magnetismus

DySBr and DySI – Synthesis, Crystal Structure, and Magnetism By reaction of Dy₂S₃ with Dy metal and Br₂ (I₂) at 750°C (900°C), single phase crystalline DySBr (DySI) has been synthesized. Crystal structure refinement of DySBr confirms the FeOCl-type structure (R = 0.049; space group Pmmn, Z = 2, lattice parameters (in Å): a = 5.349(2), b = 4.079(2), c = 8.066(2)) which is also ascertained for DySI (R = 0.059; lattice parameters (in Å): a = 5.320(2), b = 4.168(1), c = 9.224(5)). The magnetic susceptibilities (temperature range 3.4 K – 295 K) can be described on the basis of simple models (cubic crystal field, molecular field approximation) above 5 K and 15 K respectively. The deviations at low temperature are assumed to be related essentially to Dy—Dy exchange interactions which are not adequately described with the molecular field approach.     

Diffusion-based calibration for solid-phase microextraction of benzene, toluene, ethylbenzene, p-xylene and chlorobenzenes from aqueous samples

Short-term solid-phase microextraction (SPME) was performed to test a recently proposed semi-empirical model for the prediction of concentrations of analyte in water samples from the fibre-extracted mass without further calibration. The mass uptake rates obtained for benzene, toluene, ethylbenzene and p-xylene (BTEX) differ considerably from the before published, showing that interfibre comparability is a serious issue. The relative prediction errors are between -55% for benzene and +82% for p-dichlorobenzene under optimal conditions, i.e. they are by an order of magnitude higher than originally published. A sensitivity analysis shows the dominant influence of the estimated thickness of the diffusional boundary layer around the fibre on the concentration predicted. Empirical modification of the model equation for this parameter yields satisfactory results under the conditions tested for both BTEX and the selected chlorobenzenes.     

IR Study of p–π Conjugation in 2-Substituted 4-Methylene-1,3-dioxolanes and 4-Methyl-1,3-dioxoles

Selected group frequencies of the IR spectra of a number of 2-substituted 4-methylene-1,3-dioxolanes (a) and their endocyclic isomers, 2-substituted 4-methyl-1,3-dioxoles (b), have been studied to establish their usefulness as a measure of the strength of p– conjugation in the O—C=C moieties of the title compounds. In the exo compounds (a), the C=C stretching frequencies C=C and the in-phase, out-of-plane bending (wagging) frequencies CH₂ w of the =CH₂ group were found to be linearly related, besides to each other, also to the electron-donating character of the substituents and the ¹³C NMR chemical shift of the C atom of the exocyclic CH₂ group. This suggests that the two IR group frequencies of the exo isomers are linearly related to the strength of p– conjugation in the O—C=C moiety. The C=C stretching absorption of the exo compounds in the 1600–1700 cm^–1 region appeared as a doublet, shown to arise from Fermi resonance of the C=C fundamental with the CH₂ w overtone. The C=C frequencies of the endo compounds support some previous findings of an unexpected strength of p– conjugation in the 2-alkoxy derivatives. Finally, DFT calculations at the B3LYP/6-31G* level of theory are shown to give accurate predictions of the effect of 2-substituents on the group frequencies.     

Nuclear magnetic resonance studies of sulfur inversion in bis(cyclopentadienyl)-molybdenum and -tungsten complexes with dithioethers

The metallocene thioether derivatives [Cp₂M(MeSCH₂CH₂SMe)][PF₆]₂ (1, M = MO; 2, M = W), [Cp₂Mo(SCH₂CH₂SMe)][PF₆] (3) and [Cp₂M(SCH₂CH₂S)] (4, M = Mo; 5, M = W) exhibit temperature-dependent fluxional behavior in solution, owing to the pyramidal sulfur inversion process. The activation energies for this process were determined from proton band-shape analysis in the cases of 1 (54.9 ± 2 kJ mol⁻¹), 2 (51.2 ± 4.6 kJ mol⁻¹) and 3 (30.0 ± 3.1 kJ mol⁻¹). Extended Hückel calculations on related model complexes suggest that local inversion at the sulfur atoms, rather that an inversion of the complete S---C---C---S chain, is responsible for the observed fluxional behaviour.     

A Promising MgII‐Ion‐Selective Luminescent Probe: Structures and Properties of Dy–Mn Polymers with High Symmetry

Two Dy–Mn polymers, {[Dy(L¹)₃Mn_1.5(H₂O)₃]?3.125 H₂O}_n ( 1 , L¹=pyridine‐2,6‐dicarboxylic acid) and {[Dy(L²)₃Mn_1.5(H₂O)₆]?8.25 H₂O}_n ( 2 , L² = 4‐hydroxylpyridine‐2,6‐dicarboxylic acid), with high symmetry (S₆) have been prepared. Polymer 1 has a nanoporous 3D framework with channel of about 17.6 Å diameter, while 2 has a honeycomb‐type 2D structure with the cavity of approximately 14.4 Å diameter. In the construction of multidimensional porous polymers with 3d–4f mixed metals, it is the first observation that a ligand substituent effect leads to dramatic differences in the structures formed. Luminescent studies reveal that the emission intensities of 1 and 2 increase significantly upon the addition of Mg²⁺, whereas the introduction of other metal ions leaves the intensity unchanged or even weakens it; hence, both of them may serve as good candidates of Mg²⁺ luminescent probes. To our knowledge, complex 1 is also the first example of a 3d–4f metal‐based nanoporous polymer to exhibit luminescent selectivity for Mg²⁺. Magnetic susceptibility measurements reveal a rather rare ferromagnetic interaction in 2 . Thermal gravimetric analyses and powder X‐ray diffraction investigations have also been performed, suggestive of high thermal stability of 1 .     

Complexation of 6-Deoxy-6-(aminoethyl)amino-β-cyclodextrin with Sodium Cholate and Sodium Deoxycholate

In order to study its guest binding and the inclusion phenomena, 6-deoxy-6-(aminoethyl)amino--cyclodextrin (CDN) was synthesised and its binding properties examined. The complexation phenomena of sodium cholate (NaC) and sodium deoxycholate (NaDC) with CDN has been monitored by the NMR method using ¹³C chemical shift data. The method of continuous variation Job's method has been used to determine the stoichiometry of these supramolecular complexes. The Job's plot confirms the 1 : 1 supramolecular complex for NaC: CDN and the 1 : 2 supramolecular complex for NaDC: CDN. The interaction of NaC and NaDC with CDN has been obtained through two-dimensional Rotational Nuclear Overhauser Effect Spectroscopy (ROESY) NMR. Equilibrium constants were also obtained from ¹³C chemical shift data (C-1, C-3 & C-4) at different pH values (7, 9, & 11).     

能量选择中子成像技术及其应用

能量选择中子成像技术是利用特定范围波长(能量)的中子进行成像。在热/冷中子范围内(<25meV),能量选择中子成像技术主要基于布拉格边效应和衍射机制,相比常规中子成像技术不但可以显著提高图像对比度,而且能分析应变、应力、织构。在超热中子范围内(>1eV),能量选择中子成像技术主要基于中子共振吸收,中子截面随能量变化是同位素特有的,存在明显的共振吸收峰,因此可以进行同位素的“指纹”识别。能量选择中子成像技术在工程、材料、化学、物理、生物、考古等众多科研领域中有着非常广阔的应用前景。     

宇宙射线缪子成像技术在中国的研究进展

宇宙射线缪子成像是一种新型的绿色核成像技术,近年来发展迅速。该技术利用天然的缪子射线对物体实现无损、高精度的三维成像。国内多所高校和研究机构已开展了一些缪子成像技术的相关研究,包括系统研发、场景应用和少量的成像算法研究。本文针对两种不同原理的缪子成像在国内的研究进行了综述,通过一些典型案例的介绍,展现该技术在经济、文化和社会方面的巨大价值和潜力。我国幅员辽阔、工业体系完善,缪子成像技术在多个领域具有广泛的应用需求。随着相关研究的深入推进,该技术在未来将取得持续发展并得到广泛应用,在文物保护与挖掘、矿藏勘探、基础设施结构监测、泥石流自然灾害预警等产业端发挥重要作用。