Ternäre Thalliumplatin- und Thalliumpalladiumchalkogenide Tl2M4X6. Synthesen,Kristallstruktur und Bindungsverhältnisse

Ternary Thallium Platinum and Thallium Palladium Chalcogenides Tl₂M₄X₆. Syntheses, Crystal Structures, and Bonding Relations The compounds Tl₂Pt₄S₆, Tl₂Pt₄Se₆, Tl₂Pt₄Te₆ and Tl₂Pd₄Se₆ can be synthesized by a melting reaction from the elements or by the reaction of thallium carbonate, transition metal powder and chalcogen powder in the temperature range between 400°C and 950°C. X-Ray investigations on single crystals and powdered samples revealed a new structure type for the compounds, that can be understood as stacking variant of the already known atom arrangement of the alkaline metal platinum chalkogenides A₂Pt₄X₆ (A ? alkaline metal, X ? S, Se). The short distances thallium-platinum and thallium-palladium, respectively, as well as the results of Extended-Hückel-calculations indicate covalent bonds between the main group and transition metal atoms.     

Methods for the Synthesis of μ-Hydrocarbon Transition Metal Complexes without Metal–Metal Bonds

Transition metal complexes in which hydrocarbons serve as σ,σ-, σ,π- or π,π-bound bridging ligands are currently of great interest. This review presents efficient and directed syntheses for such compounds, which often have very aesthetic structures. These reactions are among the most important reaction types in modern organometallic chemistry. They can be a useful aid for the synthesis of tailor-made compounds, for example, for models of catalytic processes and, specifically, for the construction of heterometallic compounds. We will discuss reactions of electrophilic complexes with nucleophilic ones, numerous transformations of (functionalized) hydrocarbons with metal complexes, the currently very topical complexes with bridging acetylide and carbide ligands, and organometallic polymers, which can be expected to have interesting and novel materials properties. Chisholm

1 M. H. Chisholm, Polyhedron 1988 , 7, 757–1077.

has described the importance of these complexes as follows: “Central to the development of polynuclear and cluster chemistry are bridging ligands and central to organometallic chemistry are metal–carbon bonds. Thus bridging ligands hold a pivotal role ins the development of Binuclear and polynuclear organometallic chemistry”.     

De novo prediction of ground state multiplicity and structural isomerism for transition metal complexes

Prediction of the ground state geometries and multiplicities for 33 transition metal tetrachlorides has been carried out using two different levels of quantum mechanics: semiempirical and density functional theory. All data regarding geometry and spin state provided by both computational methods were compared with experimental data when available. The calculations were performed for all possible spin multiplicities. The most important geometries for coordination number four (tetrahedral, square-planar, dodecahedral, and disphenoidal), as well as less symmetric structural isomers, were evaluated. A match between both computational methods in terms of predicted ground state multiplicity and geometry was found for 26 species, which translated into almost 80% agreement. Even though the PM3(tm) geometry prediction protocol involved more steps for isolating a feasible global minimum, the aggregate of these calculations was still orders of magnitude faster than DFT calculations using extended basis sets. The calculations indicate that caution is needed in the application of the PM3(tm) method to very high-spin transition metal complexes, but point to the suitability of very rapid semiempirical methods for reliable prediction of structural and ‘spin’ isomers, and hence their use in an efficient de novo design protocol for transition metal complexes.     

Diene,Alkyne, Alkene,and Alkyl Complexes of Early Transition Metals: Structures and Synthetic Applications in Organic and Polymer Chemistry

An unprecedented series of highly reactive alkene-and diene-complexes of the early transition metals (Groups 3A–5A of the periodic system) have been isolated recently. Diene complexes of this sort (M ? Ti, Zr, Hf, Nb, Ta) prefer, besides the (η⁴-s-cis-diene)metal structure, either a novel bent η⁴-metallacyclo-3-pentene structure or the unique (η⁴-s-trans-diene)metal structure. In bis(diene)metal complexes of Nb and Ta the η⁴-s-cis-dienes assume an unusual exo-endo (supine-prone) geometry. The M? C bonds in these diene-metal complexes generally exhibit highly polarized σ-bonding along with π-bonding character. The complexes therefore undergo a variety of regio- and stereoselective carbometalations with substrates containing C? C, C? O, or C? N multiple bonds. Examples of the products that can be obtained include ketones, vinyl ketones, unsaturated primary, secondary, and tertiary alcohols, as well as diols and unsaturated acids. Mechanistic studies on the stoichiometric and catalytic conversions of unsaturated hydrocarbons provides, inter alia, some insights into the course of polymerization reactions.     

Effect of hetero atom on the conformational stability of the forming ring in the transition structures of Type-II ene cyclization: a theoretical study

The chair conformation of the forming ring in the transition structure, for its high stability, is usually considered for the determination of the overall stereoselectivity in a type-II ene cyclization reaction. However, present theoretical investigation reveals that the presence of a heteroatom like oxygen or nitrogen in the tether of type-II carbonyl ene cyclization stabilizes the transition structure, in which the forming ring adopts a boat conformation. Due to such stability of the boat conformer the overall stereoselectivity of some type-II reactions may differ from the expected one.     

Vibrational intensities of liquid N-methylpiperidine

Thin film transmission spectra of liquid N-methylpiperidine were measured in the 4000–500 cm⁻¹ region, using cells of thicknesses ranging from 1 to 8.2 μm. The spectra of both components of the complex refractive index were determined from these data in the mid-IR. Vibrational intensities and other spectral data were calculated from the k(ν) spectrum. In this region 41 bands were detected and quantitatively described. The assignment of numerous bands was carried out. The results were compared with available literature data.     

Development of a new fluorescent probe for transition metal cations based upon fluorescence resonance energy transfer

A novel fluorescent probe for metal cations, which has a large Stokes shift, was synthesized from the reaction of N-(3-carboxy-2-naphthyl)-ethylenediamine-N,N′,N′-triacetic acid (CNEDTA) with 4-(N,N-dimethylaminosulfonyl)-7-(2-aminoethylamino)-2,1,3-benzoxadiazole (DBD-ED). The large Stokes shift is due to the FRET phenomenon between a donor (CNEDTA) and an acceptor (DBD-ED) fluorophore. When the fluorescent probe, DBD-ED-CNEDTA, was excited at 240, 340 and 440 nm, an emission maximum was observed only at 560 nm. However, the fluorescence (FL) at 480 nm, based upon the CNEDTA moiety, was not detected with excitation at 340 nm. The FL intensity of DBD-ED-CNEDTA was dependent upon the acidity of the medium and highest at pH 4.1. DBD-ED-CNEDTA reacted with metal cations, i.e., Zn, Cd, Al, Y, and La, in aqueous medium to form chelates. The spectral change of FL excitation and emission was small before and after the addition of the metal ions. However, the FL intensity was dependent upon the concentrations of the metal ions. In the case of Zn²⁺, the molar ratio bound with DBD-ED-CNEDTA was calculated as 1:1. The FL intensities after chelate formation of Zn/DBD-ED-CNEDTA (1:1) were enhanced by 3.8-fold (excitation at 340 nm, emission at 560 nm), 4.2-fold (excitation at 440 nm, emission at 560 nm), and 5.9-fold (excitation at 240 nm, emission at 560 nm), respectively. The FL probe was applied to the determination of Zn in a food supplement.     

Initiating efficiency of poly(ethylene glycol)-based initiators for transition metal mediated living radical polymerisation

The kinetics of the copper mediated living radical polymerisation of methyl methacrylate initiated by [poly(ethylene glycol) methyl ether]-based initiators (MeOPEG) of various molecular weights was followed by ¹H NMR. The initiator efficiency of the macroinitiators was investigated. It was found that temperature and solvent have little effect on the reactivity of the macroinitiator, whilst chain length affects greatly the MeOPEG initiating efficiency. Steric hindrance is thought to be a main drawback, as difficult access of the monomer to the MeOPEG active chain-end and coordination of the copper catalyst to the MeOPEG chains can prevent the monomer to react with the macroinitiator.     

The vibrational spectra of the elementoorganic starburst dendrimers

The main features of vibrational spectra of starburst dendrimers have been analyzed for the first time. Their spectral pattern, in general, is determined by the ratio of a number of terminal groups to a number of repeating units. This ratio tends to m_r−1 (m_r — branching functionality of repeating unit), and becomes constant, when the generation number of the starburst dendrimer increases higher than 3-5. IR and Raman spectra of twelve generations of the phosphorus-containing dendrimers are represented and interpreted on the basis of the calculation of frequencies of the normal vibrations and band intensities in the IR spectra of ‘molecules’ terminated by dangling methyl groups, which are the fragments of the dendrimer molecule. Tailored spectra of these fragments are then compared with experimental spectra and satisfactory similarity has been obtained. Experimental spectra of generations higher than 4 are very similar, according to the theoretical approach. The results can be used for the analysis of the chemical and physical transformations in starburst dendrimers.     

含间苯基聚醚醚酮酮的合成与性能研究

含间苯基聚醚醚酮酮的合成与性能研究林权，王一凡，张万金，吴忠文，尹玖梅（吉林大学化学系，长春，１３００２３）（中国科学院长春应用化学研究所）关键词聚醚醚酮酮，间苯基，熔点，玻璃化转变温度聚芳醚酮类高聚物具有优异的热、电、机械性能．全对苯基位聚醚醚酮酮...