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1.
To gain more insight into the reactivity of intermetalloid clusters, the reactivity of the Zintl phase K12Sn17, which contains [Sn4]4? and [Sn9]4? cluster anions, was investigated. The reaction of K12Sn17 with gold(I) phosphine chloride yielded K7[(η2‐Sn4)Au(η2‐Sn4)](NH3)16 ( 1 ) and K17[(η2‐Sn4)Au(η2‐Sn4)]2(NH2)3(NH3)52 ( 2 ), which both contain the anion [(Sn4)Au(Sn4)]7? ( 1 a ) that consists of two [Sn4]4? tetrahedra linked through a central gold atom. Anion 1 a represents the first binary Au?Sn polyanion. From this reaction, the solvate structure [K([2.2.2]crypt)]3K[Sn9](NH3)18 ( 3 ; [2.2.2]crypt=4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) was also obtained. In the analogous reaction of mesitylcopper with K12Sn17 in the presence of [18]crown‐6 in liquid ammonia, crystals of the composition [K([18]crown‐6)]2[K([18]crown‐6)(MesH)(NH3)][Cu@Sn9](thf) ( 4 ) were isolated ([18]crown‐6=1,4,7,10,13,16‐hexaoxacyclooctadiene, MesH=mesitylene, thf=tetrahydrofuran) and featured a [Cu@Sn9]3? cluster. A similar reaction with [2.2.2]crypt as a sequestering agent led to the formation of crystals of [K[2.2.2]crypt][MesCuMes] ( 5 ). The cocrystallization of mesitylene in 4 and the presence of [MesCuMes]? ( 5 a ) in 5 provides strong evidence that the migration of a bare Cu atom into an Sn9 anion takes place through the release of a Mes? anion from mesitylcopper, which either migrates to another mesitylcopper to form 5 a or is subsequently protonated to give MesH.  相似文献   

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.  相似文献   

5.
The number of possible applications of NMR spectroscopy has rapidly increased during the past few years. New fields of applications have been opened by the development of supraconducting solenoids and various spin-decoupling techniques and by the method of “pulsed Fourier transform NMR-spectroscopy”. These methods originate mainly from progress in instrumentation. Recently, another “technique” has been introduced into NMR spectroscopy, which—principally on the basis of chemical and spectroscopic experience—is much less expensive but nevertheless useful. The basic principles, background, and most important applications of this method, known as the “NMR-shift-reagent technique”, form the subject of this paper.  相似文献   

6.
Serviceable NMR spectra can, with a few exceptions[1,6], be recorded for paramagnetic complexes in solution. These spectra provide information about the structure of the complexes and the distribution of the unpaired electrons, and hence also about reactive centers in the molecule. The elucidation of intermolecular and intramolecular exchange phenomena, e.g. the determination of ligand exchange rate constants, the determination of rotation barriers, and the detection of contact complexes in solution, or even of occupation equilibria of the electrons, is possible in this way. It can be seen, therefore, that NMR studies on paramagnetic complexes can be a rich source of information.  相似文献   

7.
The synthesis of a series of m‐terphenyl‐substituted tetrafluorosilicates with different cations (Na+, K+, Rb+, Cs+, Ag+, Tl+) is described and the interactions between the anion and cation are investigated in the solid, solution, and gas states by using multinuclear NMR spectroscopy, X‐ray diffraction, and ion cyclotron resonance Fourier‐transform mass spectrometry (ICR‐FT‐MS). In solution, heteronuclear NMR spectroscopy parameters show only limited sensitivity to the nature of the cation, which furthermore can be affected by solvent effects. More pronounced effects are observed in the structural data obtained from X‐ray diffraction studies, which are in good agreement with experimental gas‐phase data from ESIMS. ESIMS also reveals the existence of dimeric species of the type [M(DmpSiF4)2]? (Dmp=2,6‐dimesitylphenyl), the stability of which was determined by normalized collision energy experiments.  相似文献   

8.
Rotations and inversions in organic molecules are readily recognizable from the temperature dependence of the NMR spectra. The study of the effects of substituents on the activation barriers of such processes permits the elucidation of reaction mechanisms, and the stability limits of isomers can also be determined. The knowledge of the stability limits is necessary for the specific synthesis of stable rotamers and invertomers.  相似文献   

9.
Modern methods of NMR spectroscopy, in particular the two-dimensional techniques, offer new chances for structure determinations in the field of organolithium compounds, where the combination of 1H-, 13C-, and 6(7)Li-NMR spectroscopy is an especially useful feature. Chemical shift correlations which also include the lithium nuclei allow a complete assignment of the 1H-, 13C-, and 6Li-NMR spectra and thereby a better characterization of the various aggregates and complexes present in solution. Spatial proximities of 6Li and 1H can be detected by nuclear Overhauser experiments, and 6(7)Li-NMR exchange spectroscopy can provide new information with regard to the mechanisms and energetics of dynamic processes like aggregate interchange and complexation. After a short resumé of the experimental aspects of the NMR spectroscopy of organolithium compounds and a discussion of the NMR parameters of these systems, new experimental techniques are presented. Areas of application of these newly conceived one- and two-dimensional NMR experiments are illustrated with selected examples. The results show that even more detailed information about the structure and reactivity of organolithium compounds, which are so important for organic synthesis, can be expected in the future.  相似文献   

10.
The introduction of Fourier transform methods has not only remarkably enhanced the sensitivity of high-resolution NMR spectroscopy, thus allowing measurements to be made on less sensitive nuclei of the Periodic Table, but also has paved the way for the development of a large number of new experimental techniques. On the one hand, procedures already known have been improved and can now be performed more rapidly, and, on the other, completely new experimental approaches have become available. This situation resulted mainly from the introduction of programmable pulse transmitters and the separation of the experiment into preparation, evolution, and detection. In particular, the concept of two-dimensional spectroscopy has opened up new possibilities important for the analysis of complicated spectra and is able to provide information previously not accessible. As elsewhere, optimum application of the techniques and correct interpretation of the results require sound understanding of the underlying physical principles. Since a rigorous mathematical treatment is complicated and does not necessarily improve the comprehensibility, this article attempts to give an illustrative presentation of the new pulse techniques within the framework of the Bloch vector model. After a short introduction covering the basic principles, one-dimensional pulse techniques that can be applied using standard experimental equipment are dealt with. The main areas of application are signal assignment, sensitivity enhancement for measurements on less abundant nuclei, and selective excitation of individual resonances. Subsequently, the various techniques of two-dimensional NMR spectroscopy are treated: these enable shift correlations for different types of nuclei to be made, the presentation of spin multiplets without overlap, and the analysis of geometrical relations as well as of chemical exchange phenomena.  相似文献   

11.
Abstract

The synthesis of octahedral complexes [SnCl4L2] (L = R2NP(O)(OCH2CF3)(O-p-tolyl): R2N = Me2N (1), Et2N (2), CH2(CH2CH2)2N (3), and O(CH2CH2)2N (4), or L = R2NP(O)(OCH2CF3)(O-p-PhNO2): R2N = Me2N (5), Et2N (6), and O(CH2CH2)2N (7) is described. The new adducts have been characterized by multinuclear (31P, 19F, 119Sn) NMR, IR spectroscopy, and elemental analyses. The solution NMR data show the presence of a mixture of cis and trans isomers. The structure of the complexes in solution was further confirmed by 119Sn NMR spectra, which display a triplet for each isomer, indicating an octahedrally coordinated tin center. The effects of the nature of R and Ar substituents on the donor ability of the P=O group in the ligands R2NP(O)(OCH2CF3)(OAr) were investigated on the basis of 119Sn NMR chemical shifts and used to classify these ligands according to their Lewis basicity.  相似文献   

12.
Understanding the complex thermodynamic behavior of confined amphiphilic molecules in biological or mesoporous hosts requires detailed knowledge of the stacking structures. Here, we present detailed solid‐state NMR spectroscopic investigations on 1‐butanol molecules confined in the hydrophilic mesoporous SBA‐15 host. A range of NMR spectroscopic measurements comprising of 1H spin–lattice (T1), spin–spin (T2) relaxation, 13C cross‐polarization (CP), and 1H,1H two‐dimensional nuclear Overhauser enhancement spectroscopy (1H,1H 2D NOESY) with the magic angle spinning (MAS) technique as well as static wide‐line 2H NMR spectra have been used to investigate the dynamics and to observe the stacking structure of confined 1‐butanol in SBA‐15. The results suggest that not only the molecular reorientation but also the exchange motions of confined molecules of 1‐butanol are extremely restricted in the confined space of the SBA‐15 pores. The dynamics of the confined molecules of 1‐butanol imply that the 1H,1H 2D NOESY should be an appropriate technique to observe the stacking structure of confined amphiphilc molecules. This study is the first to observe that a significant part of confined 1‐butanol molecules are orientated as tilted bilayered structures on the surface of the host SBA‐15 pores in a time‐average state by solid‐state NMR spectroscopy with the 1H,1H 2D NOESY technique.  相似文献   

13.
Solid-state l3C CP/MAS spectral analysis of the hydrolysis products of Sn(OAc)4 allowed the hydrolysis intermediates, Sn(OH)(OAc)3, Sn(OH)2(OAc)2 and Sn(OH)3(OAc), to be identified. The results show that the hydrolysis consists of three steps; the first and second steps are consecutive reactions and the third is reversible. Intermolecular exchange between hydrolysis products (i.e. Sn(OAc)4, Sn(OH)(OAc)2, Sn(OH)2(OAc)2 and Sn(OH)3(OAc),) and acetic acid was observed from the measurement of 1H and 13C solution spectra at varied temperatures in CD2Cl2 with ΔG?348 50.5 kJ mol?1.  相似文献   

14.
An important development in the field of NMR spectroscopy has been the advent of hyperpolarization approaches, capable of yielding nuclear spin states whose value exceeds by orders‐of‐magnitude what even the highest‐field spectrometers can afford under Boltzmann equilibrium. Included among these methods is an ex situ dynamic nuclear polarization (DNP) approach, which yields liquid‐phase samples possessing spin polarizations of up to 50 %. Although capable of providing an NMR sensitivity equivalent to the averaging of about 1 000 000 scans, this methodology is constrained to extract its “superspectrum” within a single—or at most a few—transients. This makes it a poor starting point for conventional 2D NMR acquisition experiments, which require a large number of scans that are identical to one another except for the increment of a certain t1 delay. It has been recently suggested that by merging this ex situ DNP approach with spatially encoded “ultrafast” methods, a suitable starting point could arise for the acquisition of 2D spectra on hyperpolarized liquids. Herein, we describe the experimental principles, potential features, and current limitations of such integration between the two methodologies. For a variety of small molecules, these new hyperpolarized ultrafast experiments can, for equivalent overall durations, provide heteronuclear correlation spectra at significantly lower concentrations than those currently achievable by conventional 2D NMR acquisitions. A variety of challenges still remain to be solved before bringing the full potential of this new integrated 2D NMR approach to fruition; these outstanding issues are discussed.  相似文献   

15.
After outlining the chemical features and properties which make zeolites such an important group of catalysts and sorbents, the article explains how high-resolution solid-state NMR with magic-angle spinning reveals numerous new insights into their structure. 29Si-MAS-NMR readily and quantitatively identifies five distinct Si(OAl)n(OSi)4-n structural groups in zeolitic frameworks (n = 0, 1,….4), corresponding to the first tetrahedral coordination shell of a silicon atom. Many catalytic and other chemical properties of zeolites are governed by the short-range Si, Al order, the nature of which is greatly clarified by 29Si-MAS-NMR. It is shown that, as expected from Pauling's electroneutrality principle and Loewenstein's rule, both in zeolite X and in zeolite A (with Si/Al = 1.00) there are no ? Al? O? Al? linkages. In zeolite A and zeolite X with Si/Al = 1.00 there is strict alternation of Si and Al on the tetrahedral sites. Ordering models for Si/Al ratios up to 5.00 (in zeolite Y) may also be evaluated by a combination of MAS-NMR experiments and computational procedures. 29Si-MAS-NMR spectra reveal the presence of numerous crystallographically distinct Si(OSi)4 sites in silicalite/ZSM-5, suggesting that the correct space group for these related porosilicates is not Pnma. 27Al-MAS-NMR clearly distinguishes tetrahedrally and octahedrally coordinated aluminum, proving that, contrary to earlier claims, Al in silicalite is tetrahedrally substituted within the framework. In combination, 29Si- and 27Al-MAS-NMR is a powerful tool for monitoring the course of solid-state processes (such as ultrastabilization of synthetic faujasites) and of gas-solid reactions (dealumination of zeolites with silicon tetrachloride vapor at elevated temperatures). They also permit the quantitative determination of framework Si/Al ratios in the region 1.00 < Si/Al < 10 000. Since most elements in the periodic table may be accommodated within zeolite structures, either as part of the exchangeable cations or as building units of the anionic framework, there is immense scope for investigation by MAS-NMR and its variants (cross-polarization, multiple pulse and variable-angle spinning) of bulk, surface and chemical properties. Some of the directions in which future research in zeolite science may proceed are adumbrated.  相似文献   

16.
The addition of Sn and Zn ions to [Ge9] clusters by reaction of [Ge9]4? with SnPh2Cl2, ZnCp*2 (Cp*=pentamethylcyclopentadienyl), or Zn2[HC(Ph2P=NPh)2]2 is reported. The resulting Sn‐ and Zn‐bridged clusters [(Ge9)M(Ge9)]q? (M=Sn, q=4; M=Zn, q=6) display various coordination modes. The M atoms that coordinate to the open square of a C4v‐symmetric [Ge9] cluster form strong covalent multicenter M?Ge bonds, in contrast to the M atoms coordinating to triangular cluster faces. Molecular orbital analyses show that the M atoms of the Ge9M fragments coordinate to a second [Ge9] cluster with similar orbitals but in different ways. The [Ge9Sn]2?unit donates two electrons to the triangular face of a second [Ge9]2? cluster with D3h symmetry, whereas [Ge9Zn]2?acts as an electron acceptor when interacting with the triangular face of a D3h‐symmetric [Ge9]4? unit.  相似文献   

17.
The article describes the syntheses and extraction properties of a new calixarenebased extractant 5, which has been synthesized from5,11,17,23-tetra-tert-butyl-25,27-bis(chlorocarbonyl-methoxy)-26,28-dihydroxycalix[4]arene(4) by treatment with isoniazid (isonicotinic acid hydrazide) in the presence ofpyridine. The compound 5 was converted to its methyl iodide salt (6) by refluxing 5 with methyl iodide in acetonitrile. In this synthesis it was thought to explore the role of pyridinium sites in the extraction of HCr2O 7 - /Cr2O 7 2- anions. The complexing properties of 5 toward selected alkali/transition metal cationsand HCr2O 7 - /Cr2O 7 2 - anions are reported. It has been observed that receptor 5 does not extract alkali metal cations but shows an excellent selectivity toward transition metals. The protonated pyridinium form of 5 is an effective formfor transferring the HCr2O 7 - /Cr2O 7 2- anions from an aqueous into adichloromethane layer.  相似文献   

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19.
An NMR spectroscopic technique has been developed to give rapid, accurate pH measurements on tenth-milliliter samples of concentrated acidic aqueous solutions buffered by fluoride ion in the pH 1.5-4.5 range. The fluoride 19F chemical shift has been calibrated as a function of pH at 0.1 and 1.0 M concentration by reference to an internal 3-fluoropyridine standard. Subsequent measurements of fluoride buffer pH required no additives and only two NMR spectra in the presence of an external reference standard.  相似文献   

20.
合成了二正丁基锡新型配合物(n-Bu)2Sn(FcCOS)2[Fe=(η-C5H5)Fe(1-5-η-C5H4)-1;研究了该配合物的红外光谱和核磁共振(1H,13C,119Sn)谱,并推测出配合物可能的分子结构。  相似文献   

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