Vinylacetylene chemistry

It is shown that heating vinylacetylenic piperidols I with phosphorus oxychloride in pyridine solution gives dienynes II, the structure of which is determined, in the case of II (R=H), by means of IR spectra and PMR. Hydration of the dienynes II (R=H, Me) in the presence of mercuric sulfate in methanol solution gives -methoxyketones III (R=H, Me). It is also shown that III and aqueous solutions of ammonia or primary amines give the bicyclic piperid-4-ones IV. In the synthesis of IV (R=H, R₁ = i-Pr, Bu) imines V are obtained, which on hydrolysis give piperidones IV (R = H, R₁ = i-Pr, Bu). When the ß-methoxyketone III (R = H) is heated with 5% sulfuric acid in the presence of mercuric sulfate, chroman-4-one is formed.     

The chemistry of ethyleneimine

The structure of the products of the reaction of -hydrazinoethyl hydrogen sulfate with aldehydes has been studied. In an alkaline media, the condensation products are converted into hydrazones of N-aminoethyleneimine or the corresponding azines. The structure of the cyclization products was shown by UV, IR, and PMR spectroscopy.For part IV, see [1].     

Nuclear techniques in structural chemistry

The discovery of radioactivity started the nuclear research. The nuclear techniques are very powerful tools in structural chemistry, as well. We would like to support this statement by two examples in this paper. We present a series of Mössbauer measurements which give information about the coordination structure of some dibutyltin (IV) complexes of carbohydrate derivates. The other example will demonstrate how the positron lifetime spectra can reflect the temperature dependence of water structure.     

Structural chemistry of organotin(IV) complexes

The amazing structural diversity in organotin compounds is discussed in the systems containing -O and -S donor ligands. It is demonstrated that there exist a fascinating range of structural diversity for organotin(IV) complexes, including differences in coordination number and molecular geometry. The difference in structure is correlated with the nature of tin and ligand bonded R groups. Despite the large number of different structures found in organotin(IV) carboxylates, there is limited range of coordination geometries about the Sn atom. The four coordinated Sn atom in triorganotin(IV) complexes is invariably distorted tetrahedral and five coordinated Sn is distorted trigonal bipyramidal. A large range has been observed for diorganotin carboxylate structures, where five, six and seven coordinate geometries have been reported. The Sn atom in mono-organotin has only been demonstrated to exist in distorted octahedral geometries (the single exception being a pentagonal bipyramidal geometry). In the case of organotin(IV) complexes of S donor ligands, it has been shown that there exists a rich diversity in Sn atom geometries and coordination modes of the sulfur donor ligands themselves. As in related carboxylate systems, the assignment of coordination numbers to the Sn centers in some compounds is controversial. As a general trend, it has been shown that, the overall coordination number at the Sn atom decreases with the increasing number of organic substituents at the Sn atom. This phenomenon is usually achieved by increased asymmetry in the mode of coordination of the sulfur donor ligands.     

Synthesis and coordination chemistry of organotin(IV) complexes of 2,3-methylenedioxyphenylpropenoic acid

The synthesis, spectroscopy, and antitumor behavior of organotin(IV) complexes of 2,3-methylenedioxyphenylpropenoic acid are described. The spectroscopic data indicate 1 : 2 and 1 : 1 metal to ligand stoichiometry in case of di- and trioganotin(IV) compounds and hypervalency of Sn(IV) in trigonal bipyramidal and octahedral modes. Mass spectrometric and elemental analysis data support the solid and solution spectroscopic results. The complexes have been evaluated in vitro against crown gall tumor and bio-activity screenings showed in vitro biological potential. The nature of covalent attachments (methyl, ethyl, n-butyl, phenyl, and n-octyl) of Sn(IV) played a decisive role for bioactivity. All the compounds have been studied in solution by NMR (¹H, ¹³C) and also in solid state using FTIR, mass spectrometry, and by X-ray crystallography. The molecular structure of Et₂Sn(IV) and Me₃Sn(IV) derivatives confirm the behavior of di- and tri-organotin(IV) compounds in solid state. Mono-organotin derivatives are octahedral both in solid and solution.     

Further examples of the failure of surrogates to properly model the structural and hydrothermal chemistry of transuranium elements: insights provided by uranium and neptunium diphosphonates

In situ hydrothermal reduction of Np(VI) to Np(IV) in the presence of methylenediphosphonic acid (C1P2) results in the crystallization of Np[CH2(PO3)2](H2O)2 (NpC1P2-1). Similar reactions have been explored with U(VI) resulting in the isolation of the U(IV) diphosphonate U[CH2(PO3)2](H2O) (UC1P2-1), and the two U(VI) diphosphonates (UO2)2[CH2(PO3)2](H2O)3.H2O (UC1P2-2) and UO2[CH2(PO3H)2](H2O) (UC1P2-3). Single crystal diffraction studies of NpC1P2-1 reveal that it consists of eight-coordinate Np(IV) bound by diphosphonate anions and two coordinating water molecules to create a polar three-dimensional framework structure wherein the water molecules reside in channels. The structure of UC1P2-1 is similar to that of NpC1P2-1 in that it also adopts a three-dimensional structure. However, the U(IV) centers are seven-coordinate with only a single bound water molecule. UC1P2-2 and UC1P2-3 both contain U(VI). Nevertheless, their structures are quite distinct with UC1P2-2 being composed of corrugated layers containing UO 6 and UO 7 units bridged by C1P2; whereas, UC1P2-3 is found as a polar three-dimensional network structure containing only pentagonal bipyramidal U(VI). Fluorescence measurements on UC1P2-2 and UC1P2-3 exhibit emission from the uranyl moieties with classical vibronic fine-structure.     

The structure and chemistry of hydroxylycoctonine

The observed physical properties and some selected reactions define hydroxylycoctonine as IV and its anhydronium salts as III.     

Metallocene carbene chemistry

The Group IV bent metallocenes Cp₂M (M = Ti, Zr, Hf) were involved in carbene-related chemistry in various ways. Examples from four different areas are used to illustrate this. In situ generated Cp₂M: species exhibit some carbene-like character. They add to olefins, and their addition products can incorporate additional unsaturated organic reagents, e.g., alkyne, to form five-membered metallacycles. The high oxophilicity of the Group IV metals helps the addition of alkene-, aryne-, ²-ketone-, ²-aldehyde-, or butadiene-containing reagents to a great variety of metal carbonyl compounds to form the Fischer-type carbene complexes. The resulting zirconoxycarbene complexes have found some application in organometallic chemistry and in organic synthesis. Reactive [Cp₂M^IVR]⁺ cations can be stabilized by the addition of the Arduengo carbenes that serve as bulky two-electron donor ligands. First examples were structurally characterized. Dialkylimidazol-2-ylidenes also add to the electrophilic MX₄ compounds yielding stable trans-bis(imidazol-2-ylidene)MX₄ systems. Several examples are presented where ruthenium carbene complexes are used for carrying out catalytic olefin metathesis reactions at pendant olefinic substituents at the bent metallocenes. These reactions have led to the formation of novel bimetallic metallocene systems, as well as to new ansa-metallocenes. These catalytic reactions have helped in the current efforts to develop a functional group chemistry at the sensitive Group IV bent metallocene frameworks.     

Coordination chemistry at the molybdenum site of sulfite oxidase: redox-induced structural changes in the cysteine 207 to serine mutant

The redox chemistry of the molybdenum site of the C207S mutant of recombinant human sulfite oxidase has been studied via potentiometric titrations employing both electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS) as probes of the active site structure. In earlier EXAFS studies, oxidized Cys207Ser enzyme has been shown to possess a novel tri-oxo active site, in which Ser207 does not appear to be a ligand to Mo [George, G. N.; Garrett, R. M.; Prince, R. C.; Rajagopalan, K. V. J. Am. Chem. Soc. 1996, 118, 8588-8592]. Redox titrations show that the active site is modified under reducing conditions to a mono-oxo Mo(IV) species, probably with Ser207 ligated to the metal. The Mo(IV) species can be reoxidized to a mono-oxo Mo(V) species still coordinated to Ser207, which in turn can be further reoxidized to yield the initial tri-oxo Mo(VI) structure with loss of Ser207 ligation.     

Radiation chemistry of actinides

The paper presents data on the development of a mathematical model describing the radiation-chemical behaviour of plutonium in 3–6 mol/l HNO₃ with uranium present and absent. Using experimental data on the kinetics of Pu(VI) reduction and Pu(IV) oxidation, and comparing them with the calculated values, we succeeded in finding the previously unknown rate constants of many reactions between plutonium ions and HNO₃ radiolysis products, between plutonium ions and between plutonium ions and uranium ions. The mechanism of the radiation-chemical processes has been established.     

The fixation of linear versus loop-type peptidic structures by metal coordination: the coordination chemistry of Val-Val- and Val-Val-Val-bridged dicatechol ligands

The Val-Val-bridged dicatechol ligand L1-H4 forms triplybridged dinuclear complexes with titanium(IV) ions, while the more flexible Val-Val-Val derivative L2-H4 leads to mixtures of complexes containing species with a cyclic arrangement of the ligand; with [cis-MoO2]2+ on the other hand, a well-defined macrocycle [(L2)MoO2]2- is formed which possesses a loop-type structure in the peptidic part of the ligand.     

Group 4 complexes of a new [OSSO]-type dianionic ligand. Coordination chemistry and preliminary polymerization catalysis studies

A straightforward synthesis of a new type of tetradentate dianionic [OSSO]-type ligand is described. This ligand features an ethylenedithiol core bridged via methylene groups to substituted phenols, thus representing an S analogue of the [ONNO]-type Salan ligands. The [OSSO]H2 ligand precursor reacted with titanium(IV) isopropoxide and with zirconium(IV) tert-butoxide to give the corresponding [OSSO]-M(OR)2 complexes, which formed as single C2-symmetric isomers but were fluxional according to variable-temperature NMR. An X-ray structure of [OSSO]-Zr(O-t-Bu)2 supported the fac-fac wrapping mode of the ligand. The dibenzyl complex [OSSO]-Zr(bn)2 that was obtained by a reaction between the ligand precursor and tetrabenzylzirconium was found to be an active 1-hexene polymerization catalyst upon activation with B(C6F5)3, leading to a stereoirregular polymer despite its C2 symmetry.     

Crystal chemistry of V3O5 and related structures

V₂O₃ single crystals have been grown by chemical vapor transport with HCl and TeCl₄. Crystals grown with TeCl₄ contain V₃O₅, as verified by X-ray analysis, and this affects the low temperature transition. Polycrystalline V₂O₃ has also been prepared containing various amounts of V(IV). Magnetic data for these samples demonstrate the sensitivity of V₂O₃ to small substitutions of V(IV) for V(III). A similar substitution of Ti(IV) into V₂O₃ does not result in any change in the transition temperature, although the magnitude of the transition decreases.     

Online information retrieval in analytical chemistry

Several impressive examples of online searching in the Chemical Abstracts database of CAS Online for information needed to solve typical analytical problems have been presented by Barbara M. Abler (TrAC, Vol. 6, January (1987) IV). Other databases and search services useful for information retrieval in analytical chemistry are surveyed by the author on the basis of her experience as an online search intermediary.     

Spectroscopic,electrochemical, and structural aspects of the Ce(IV)/Ce(III) DOTA redox couple chemistry in aqueous solutions

The redox potential of the Ce(IV)/Ce(III) DOTA is determined to be 0.65 V versus SCE, pointing out a stabilization of ~13 orders of magnitude for the Ce(IV)DOTA complex, as compared to Ce(IV)_aq. The Ce(III)DOTA after electrochemical oxidation yields a Ce(IV)DOTA complex with a t_1/2 ~3 h and which is suggested to retain the “in cage” geometry. Chemical oxidation of Ce(III)DOTA by diperoxosulfate renders a similar Ce(IV)DOTA complex with the same t_1/2. From the electrochemical measurements, one calculates logK (Ce(IV)DOTA^2?) ~ 35.9. Surprisingly, when Ce(IV)DOTA is obtained by mixing Ce(IV)_aq with DOTA, a different species is obtained with a 2 : 1(M : L) stoichiometry. This new complex, Ce(IV)DOTACe(IV), shows redox and spectroscopic features which are different from the electrochemically prepared Ce(IV)DOTA. When one uses thiosulfate as a reducing agent of Ce(IV)DOTACe(IV), one gets a prolonged lifetime of the latter. The reductant seems to serve primarily as a coordinating ligand with a geometry which does not facilitate inner sphere electron transfer. The reduction process rate in this case could be dictated by an outer sphere electron transfer or DOTA exchange by S₂O₃^2?. Both Ce(IV)DOTA and Ce(IV)DOTACe(IV) have similar kinetic stability and presumably decompose via decarboxylation of the polyaminocarboxylate ligand.     

Role of solution chemistry on the trapping of radionuclide Th(IV) using titanate nanotubes as an efficient adsorbent

Titanate nanotubes (TNTs) have attracted great interest in multidisciplinary study since their discovery. The adsorption of thorium [Th(IV)] onto TNTs in the absence and presence of humic acid (HA)/fulvic acid (FA) was studied by batch technique. The influence of pH from 2.0 to 10.0, ionic strength from 0.001 to 0.1 mol L^?1 NaClO₄, and coexisting electrolyte cations (Li⁺, Na⁺, K⁺) and antions (ClO₄ ^?, NO₃ ^?, Cl^?) on the adsorption of Th(IV) onto TNTs was tested. The adsorption isotherms of Th(IV) was determined at pH 3.0 and analyzed with Langmuir and Freundlich adsorption models, respectively. The results demonstrated that the adsorption of Th(IV) onto TNTs increases steeply with increasing pH from 2.0 to 4.0. Generally, HA/FA was showed to enhance Th(IV) adsorption onto TNTs at low pH values, but to reduce Th(IV) adsorption onto TNTs at high pH values. The adsorption of Th(IV) onto TNTs was also dependent on coexisting electrolyte ions in aqueous solution under our experimental conditions. The adsorption of Th(IV) onto TNTs is exothermic and spontaneous. The findings indicating that TNTs can be used as a promising candidate for the enrichment and solidification of Th(IV) or its analogue actinides from large volume solution in real work.     

Aqueous solution chemistry of alkyltin(IV) compounds for speciation studies in biological fluids and natural waters

Organotin(IV) cations behave as Lewis acids of different strength depending on the charge, according to the following acidity scale: RSn³⁺ > R₂Sn²⁺ > R₃Sn⁺. For this reason they can react with Lewis bases containing –O, –N, –S donor groups to form complex species of different stability. Complex formation of organotin(IV) moieties with a great number of inorganic and organic ligands in aqueous solution is reviewed here in the light of their environmental and biological impact. To this end, complex species formation was considered in different ionic media and at different ionic strengths, with reference to the composition of natural waters and biological fluids. In particular, the interaction of alkyltin(IV) compounds with the following ligands was taken into account: hydroxo, chloride, sulfate, fluoride, carbonate and phosphate; carboxylates, amines, amino-carboxylates, nucleotides, saccharides, S-containing ligands and antibiotics. Moreover, the interaction of organotin(IV) cations with synthetic (polyacrylate) and natural occurring (fulvic and alginic acids) polyelectrolytes was also considered. The strength of interaction is reported in terms of stability constants of complex species formed and of other thermodynamic parameters, such as formation enthalpy. The stability trend of the complexes is alkyltin(IV)-S > alkyltin(IV)-N > alkyltin(IV)-O-donor ligands. On the basis of data in the literature, empirical relationships are provided to predict the stability of alkyltin(IV) species with some classes of ligands. The complexation models proposed by the different authors for the species formation of mono-, di- and tri-alkyltin(IV) in the presence of various ligands were considered in the light of defining the speciation picture of this class of compounds in aquatic systems.     

Synthesis,structure, chemistry,and applications of tetravalent nickel complexes

This review provides an overview of the synthetic pathways, structures, and reactivity of various nickel(IV) complexes. The complexes are classified according to the various ligand types including sulfur, oxygen, nitrogen, and phosphorus donors. The main emphasis is on different ligand systems which stabilize Ni in higher oxidation state in the solid state and solution. The structural aspects of the complexes are briefly discussed. The possible applications of these nickel(IV) complexes are reviewed and future prospects are also highlighted.     

Cerium(IV)-mediated C-C bond formations in carbohydrate chemistry

We provide a comprehensive study on the addition of radicals to unsaturated carbohydrates in the presence of cerium(IV) ammonium nitrate (CAN). The method is applicable to hexoses, pentoses, and disaccharides, tolerates different protecting groups, and is characterized by mild reaction conditions. Best substrates are malonates and glycals, which afford 2-C-branched carbohydrates in high yields and stereoselectivities. For the first time, the anomeric radicals were trapped with nucleophiles after oxidation and thus the 1- and 2-position of glucose were functionalized in one step. Nitro compounds are suitable CH acidic radical precursors as well, offering an easy access to C-analogs of glycosamines in moderate to good yields. Finally, selective reductions demonstrate the synthetic potential of cerium(IV)-mediated radical reactions in carbohydrate chemistry.     

Relativistic effects in kurchatovium chemistry

Using the relativistic multiconfigurational Dirac-Fock method, the first four ionization potentials of Ku, the promotion energies of the atom, and the atomic and ionic radii were calculated. The enthalpy of sublimation of metallic Ku was estimated. Relativistic SCF-X scattering wave Dirac-Slater computations of the tetrachlorides of group IV elements were performed. The lower halides of Ku are predicted to be more stable and less volatile than the respective Hf compounds, due to the ds² p ground state in the Ku atom.