New Forms and Functions of Tellurium: From Polycations to Metal Halide Tellurides

Metal chalcogenides and metal chalcogenide halides are distinguished by their structural diversity and by their very different physical properties. Therefore, the synthesis of novel compounds from this class is always a rewarding goal for the preparatively oriented solid-state chemist. Over the past few years, many syntheses and structural investigations have stimulated the field. The emphasis of the research has been placed on selenium-rich and tellurium-rich compounds, which are characterized by directed covalent bonds between the chalcogen atoms. Compounds with novel chalcogen polycations have also become accessible during the past few years by reacting the chalcogen elements with transition metal halides, or from chemical vapor deposition in the sense of chemical transport reactions. In these compounds, tellurium differs from its lighter homologues by a pronounced tendency towards greater covalence. This article attmepts to provide an overview of new developments in the field of compounds with chalcogen polycations and of metal chalcogenide halides, with an emphasis on compounds containing molybdenum and tungsten as the transition metals and tellurium as the chalcogen.     

Probing actinide electronic structure using fluorescence and multi-photon ionization spectroscopy

The role of the 5f orbitals in actinide bond formation is one of the central issues of actinide chemistry. This question can be explored using relativistic quantum chemistry calculations, but the theoretical methods must be validated using definitive experimental data. For simple ionic compounds such as actinide oxides and halides, the electronic structure can be examined using electronic and photoelectron spectroscopy of gas phase molecules. The present article surveys recent spectroscopic and theoretical studies of the oxides of thorium and uranium. The results show that the 5f-like states are spectators and that the complex patterns of low-lying electronic states for these molecules can be understood in terms of a semi-empirical ligand field model. Comparisons with recent high-level theoretical calculations are presented and discussed.     

Molecular Dipole Evaluation Using Monolayer Films: Can Computations Link Theory with Experiments?

A novel computational approach is presented for the determination of the effective electrical dipole of amphiphile molecules in monolayers at the air‐water interface (Langmuir films). Results from ab initio computations on model compounds, combined with molecular mechanics simulations of the associated films are consistent with experimentally determined dipole data. Though presently at its preliminary stage, this method may prove helpful in elucidating structural features that are not otherwise experimentally accessible.     

Convenient and Highly Efficient Routes to 2 H‐Chromene and 4‐Chromanone Derivatives: Iodine‐Promoted and p‐Toluenesulfonic Acid Catalyzed Cascade Cyclizations of Propynols

A convenient strategy is presented for the easy preparation of a series of 2 H‐chromenes under mild conditions through iodocyclization of readily accessible propynols. In addition, various 4‐chromanones can be synthesized through a p‐toluenesulfonic acid catalyzed cascade cyclization with high efficiency (yields up to 99 %). Our developed reaction systems are proven to have good functional‐group applicability and can be scaled up to gram quantities in satisfactory yields. These systems also provide a new synthetic strategy for two types of important flavonoid skeleton without using costly and toxic metal catalysts. Additionally, the resulting halides could be further exploited in subsequent palladium‐catalyzed coupling reactions, so these compounds could act as potential intermediates for the construction of some valuable drug molecules.     

Predicting solid-state heats of formation of newly synthesized polynitrogen materials by using quantum mechanical calculations

We present density functional theory level predictions and analysis of the basic properties of newly synthesized high-nitrogen compounds together with 3,6-bis(2H-tetrazol-5-yl)-1,2,4,5-tetrazine (BTT) and 3,3'-azobis(6-amino-1,2,4,5-tetrazine) (DAAT), for which experimental data are available. The newly synthesized high-nitrogen compounds are based on tricycle fused 1,2,4-triazine and 1,2,4,5-tetrazine heterocycles. In this work, the molecules BTT and DAAT have been studied in order to validate the theoretical approach and to facilitate further progress developments for the molecules of interest. Molecular structural properties are clarified, and IR spectra predictions are provided to help detection of those compounds in the experiment. The energy content of the molecules in the gas phase is evaluated by calculating standard enthalpies of formation, by using a special selection of isodesmic reaction paths. We also include estimates of the condensed-phase heats of formation and heats of sublimation in the framework of the Politzer approach. The obtained properties are consistent with those new high-nitrogen compounds being a promising set of advanced energetic materials.     

Condensed Metal Clusters

The chemistry of metals in low valence states is marked by the frequent occurrence of metal clusters, which are easily recognizable when they occur as molecular units. Many metal-rich compounds of transition metals with p-elements (3rd to the 6th main groups) are closely related to the corresponding halides, since they are built up from metal clusters of the same type. The clusters are however, linked together (condensed) by metal-metal bonds. This principle of construction holds particularly well in the case of the novel reduced halides of the lanthanoids.     

Studying the dimerization reaction during the abstraction of halogen from organohalides by laser photoemission, controlled-potential electrolysis, and voltammetry

To continue earlier investigations into the dimerization reaction during the cathodic cleavage of a carbon-halogen bond and, in particular, to find an accessible way for synthesizing 1,4-butanediol, a comparative study of the dimerization of ethylene halohydrins and butyl and allyl halides is performed. On the basis of the data obtained by the laser photoemission (LPE), controlled-potential electrolysis, and voltammetry techniques, a general mechanism of the electrode reactions involving these compounds and their intermediates is proposed and recommendations on the optimization of the 1,4-butanediol synthesis are elaborated. According to LPE data, at pH < 8.1, the Β-hydroxyethyl radical reduction occurs with a preceding formation of a complex with a proton donor, whereas a direct electron transfer is characteristic of the butyl radical. This difference in mechanisms is offered as the main reason for the lesser capability of ethylene halohydrins to electrochemical dimerization as compared with butyl halides, where the octane yield reached up to 80–84%. The earlier assumption about a high electrocatalytic activity of the copper cathode in dimerization of ethylene halohydrins is confirmed, and possibilities of an iron cathode in this process are revealed. The dimer yield is found to increase in alkaline solutions and at lowered temperatures, specifically, at pH 11 and temperatures of 0–5°C., the 1,4-butanediol yield reached ∼17%.     

Sampling CASE Application for the Quality Control of Published Natural Product Structures

Structure elucidation with NMR correlation data is dicey, as there is no way to tell how ambiguous the data set is and how reliably it will define a constitution. Many different software tools for computer assisted structure elucidation (CASE) have become available over the past decades, all of which could ensure a better quality of the elucidation process, but their use is still not common. Since 2011, WebCocon has integrated the possibility to generate theoretical NMR correlation data, starting from an existing structural proposal, allowing this theoretical data then to be used for CASE. Now, WebCocon can also read the recently presented NMReDATA format, allowing for uncomplicated access to CASE with experimental data. With these capabilities, WebCocon presents itself as an easily accessible Web-Tool for the quality control of proposed new natural products. Results of this application to several molecules from literature are shown and demonstrate how CASE can contribute to improve the reliability of Structure elucidation with NMR correlation data.     

Adiabatic versus nonadiabatic photoisomerization in photochromic ruthenium sulfoxide complexes: a mechanistic picture from density functional theory calculations

Polypyridine ruthenium sulfoxide complexes are intriguing compounds which can display both photochromic and electrochromic properties. These properties are based on the Ru-S → Ru-O linkage isomerization capability of the sulfoxide group. The photoisomerization mechanism is of particular importance in order to understand the photophysical properties of such molecules. Density functional theory calculations demonstrate that the main photoisomerization mechanism is nonadiabatic for the system under study in agreement with the experimental observations. Indeed, funnels for efficient radiationless decay back to the ground state are shown to be easily accessible compared to transition states on the adiabatic triplet potential energy surface. However, we highlight for the first time that triplet metal-centered states play a central role in the photoisomerization mechanism of these compounds.     

A quantum-chemical approach to the analysis of intramolecular interactions using the fragment orbitals and MNDO method. Calculations for vinyl fluoride and vinyl iodide

A new quantum-chemical method for demarcation between the basic mechanisms of mutual influence of structural fragments in complex organic molecules (inductive effect, conjugation,etc.) and for assessment of their significance for particular physicochemical properties is proposed. The effects of different channels of intramolecular interaction on the molecular geometry and energy, charge distribution, and the molecular orbital structures and energies were considered taking vinyl halides as examples. In systems with an interfragment bond of high polarity, separation of the contribution of the inductive effect is to a great extent meaningless, while π-conjugation can be considered independently. The method allows a more valid interpretation of the results of quantum-chemical calculations in terms of theoretical organic chemistry.     

1,3-Cyclohexadien-1-Als: Synthesis,Reactivity and Bioactivities

In synthetic organic chemistry, there are very useful basic compounds known as building blocks. One of the main reactions wherein they are applied for the synthesis of complex molecules is the Diels–Alder cycloaddition. This reaction is between a diene and a dienophile. Among the most important dienes are the cyclic dienes, as they facilitate the reaction. This review considers the synthesis and reactivity of one of these dienes with special characteristics—it is cyclic and has an electron withdrawing group. This building block has been used for the synthesis of biologically active compounds and is present in natural compounds with interesting properties.     

The cross-coupling reactions of organic halides with organic derivatives of tin,mercury and copper catalyzed by palladium

The palladium-catalyzed cross-coupling of organic halides with organometallic compounds of tin, mercury and copper is discussed. It is shownn that the “ligandless” palladium complexes RPdXL₂ (L = solvent), in which solvent molecules act as weak donating ligands, are the most active catalysts for reactions of organotin compounds. It is found that nucleophilic catalysis is an efficient method of activatioin of organomercury and organocopper compounds in cross-coupling reactions. In the presence of iodide ion the palladium-catalyzed reactions of these compounds proceed under mild conditions giving high yields of cross-coupling products.     

Carbon-halogen bond activation by a structurally constrained phosphorus(III) platform

The σ-bond activation by main group element has received enormous attention from theoretical and experimental chemists. Here, the reaction of C–X (X = Cl, Br, I) bonds in benzyl and allyl halides with a pincer-type phosphorus(III) species was reported. A series of structurally robust phosphorus(V) compounds were formed via the formal oxidative addition reactions of C–X bonds to the phosphorus(III) center. Density functional theory calculations show that the nucleophilic addition process is more favorable than the direct oxidative addition mechanism. Isomerization of bent structures of phosphorus(III) compound to poorly nucleophilic compounds to undergo further C–X bond activation can be rationalized by frontier molecule orbital analysis. This study not only provides a deep understanding of the reactivity of phosphorus(III) species but also demonstrates a potential of main group elements for the small-molecule activation.     

Synthesis and biological activities of dithiocarbamates containing1,2,3-triazoles group

Twelve novel dithiocarbamates containing 1,2,3-trizaoles group were prepared via one step starting from organic halides, dithiocarbamic acid prop-2-ynyl ester, and sodium azide, using a very simple catalytic system composed of copper（I） chloride and water at 70 8C. The structures of the new compounds were characterized and screened for their in vitro anti-tumor. Four of the compounds displayed varying levels of anti-tumor activity against the CDC25 B.     

超价化合物

超价分子和离子是一类奇特而迷人的物种,它们的出现对经典的Ｌｅｗｉｓ－Ｌａｎｇｍｕｉｒ主族元素价层成键理论提出了挑战。本文从超价化合物的发展史、定义、理论描述、表示方法、合成、稳定性、周期性变化、光谱表征等方面对超价化合物进行了较详细的论述。     

Solid state density functional calculations for the group 11 monohalides

The group 11 monohalides are characterized by a variety of different solid-state structures and modifications. The copper halides crystallize mainly in a cubic zinc blende structure, while silver halides are mostly found in a rock salt modification. Completely different are the gold compounds where relativistic effects change the symmetry from a cubic to a chainlike AuX arrangement (X = F, Cl, Br, I) with short Au-Au internuclear distances. Here we present a systematic study of all solid state group 11 halides by scalar relativistic density functional theory for the experimentally known and observed structures, as well as for other unknown modifications and compare their relative stability.     

Molecular modeling approaches for the prediction of the nonspecific binding of drugs to hepatic microsomes

Molecular modeling approaches for the prediction of the nonspecific binding of drugs to hepatic microsomes were examined using a published database of 56 compounds. Models generated were evaluated using an independent test set of 13 compounds. A pharmacophore approach identified structural features of drugs associated with nonspecific binding. A side-chain amino group and complementary hydrophobic domain were the principal features noted. The use of shape overlays, based on the pharmacophore, in conjunction with a chemical force field in the program ROCS, yielded discrimination between molecules classified as strong binders (experimental fraction unbound in microsomes<0.50) and those with a lower degree of binding (experimental fraction unbound in microsomes>0.50). In the initial data set of 56 molecules, 18 were classified as strong binders (on the basis of the above criteria), and all of those were recovered in the top 22 molecular hits from ROCS. Additionally, computationally generated values of log P were shown to provide a reasonable estimate of the fraction unbound in microsomes, providing the compounds were in their basic form at physiological pH.     

Insertion of noble gas atoms into cyanoacetylene: an ab initio and matrix isolation study

A computational and experimental matrix isolation study of insertion of noble gas atoms into cyanoacetylene (HCCCN) is presented. Twelve novel noble gas insertion compounds are found to be kinetically stable at the MP2 level of theory, including four molecules with argon. The first group of the computationally studied molecules belongs to noble gas hydrides (HNgCCCN and HNgCCNC), and we found their stability for Ng = Ar, Kr, and Xe. The HNgCCCN compounds with Kr and Xe have similar stability to that of previously reported HKrCN and HXeCN. The HArCCCN molecule seems to have a weaker H-Ar bond than in the previously identified HArF molecule. The HNgCCNC molecules are less stable than the HNgCCCN isomers for all noble gas atoms. The second group of the computational insertion compounds, HCCNgCN and HCCNgNC, are of a different type, and they also are kinetically stable for Ng = Ar, Kr, and Xe. Our photolysis and annealing experiments with low-temperature cyanoacetylene/Ng (Ng = Ar, Kr, and Xe) matrixes evidence the formation of two noble gas hydrides for Ng = Kr and Xe, with the strongest IR absorption bands at 1492.1 and 1624.5 cm(-1), and two additional absorption modes for each species are found. The computational spectra of HKrCCCN and HXeCCCN fit most closely the experimental data, which is the basis for our assignment. The obtained species absorb at quite similar frequencies as the known HKrCN and HXeCN molecules, which is in agreement with the theoretical predictions. No strong candidates for an Ar compound are observed in the IR absorption spectra. As an important side product of this work, the data obtained in long-term decay of KrHKr+ cations suggest a tentative assignment for the CCCN radical.