Spectral and electrochemical study of coordination molecules Cu4OX6L4: 3-Methylpyridine and 4-Methylpyridine Cu4OBrnCl(6−n)L4 complexes

The tetranuclear Cu₄OBr_nCl_(6-n)L₄ complexes, where L = 3-methylpyridine (3-Mepy), 4-methylpyridine (4-Mepy) and n=0–6 with trigonal bipyramidal coordination of copper(II) were prepared and their infrared and electronic absorption spectra as well as cyclic voltammograms in nitromethane solutions were measured. The polyhedra in Cu₄OBr_nCl_(6−n) (3-Mepy)₄ molecules are less distorted comparing with those of 4-Mepy analogues as indicated by infrared Cu₄O absorptions, far infrared Cu—Br, Cu—Cl, and Cu—N absorptions, d—d bands in electronic spectra and potentials, measured by cyclic voltammetry. The 3-Mepy complexes exhibit strong single infrared Cu₄O absorptions, while for related 4-Mepy complexes doubly split Cu₄O bands were observed. Two strongly overlapped d—d bands in electronic absorption spectra of the 3-and 4-Mepy complexes in nitromethane were resolved by Gaussian fitting. The 4-Mepy ligand produces slightly stronger ligand field than its 3-Mepy analogue. The maxima of high-energy d—d bands are in a linear correlation with the number of bromide ligands. The correlations for corresponding low-energy bands are considerably deviated from linearity. The halfwave potentials of the complexes in nitromethane correlate with both the number of bromides and the data of electronic absorption spectra suggesting that the reducing electron at the electrode process enters the half-filled d _{z 2} orbital of the copper(II) atom. The origin of a difference between the 3-and 4-Mepy complexes in their spectral and electrochemical properties is also discussed.     

Influence of the pyridine methyl substituent position on the chemical changes of the NCS groups in the thermal decomposition of coordination compounds of the type Cu(NCS)2L2

The influence of the position of the CH₃ group in picoline and lutidine ligands on the degree of chemical change of the NCS groups in coordination compounds of the type Cu(NCS)₂L₂ (whereL=2-, 3- and 4-picoline, and 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-lutidine) is dealt with. The most marked effect of the CH₃ group is found to be exerted in position 4. This effect of the methyl group on the degree of chemical change points to the mutual influence of the ligands in coordination compounds of Cu(II).

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Zusammenfassung Der Artikel befaßt sich mit dem Einfluß der Lage der CH₃ Gruppe in Pikolinen und Lutidinen als Liganden auf den Grad der chemischen Änderungen der Gruppen NSC in Koordinationsverbindungen des Typs Cu(NCS)₂L₂ (L=2-, 3- und 4-Pikoline, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- und 3,5-Lutidine). Der ausgeprägteste Effekt der CH₃ Gruppe wurde in der Position 4 beobachtet. Dieser Einfluß der Methylgruppe auf das Ausmaß der chemischen Änderungen deutet auch auf die gegenseitige Wirkung der Liganden in Koordinationsverbindungen von Cu(II).

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Résumé L'article a trait à l'influence de la position du groupe CH₂ dans les picolines et lutidines, en tant que ligands, sur le degré des changements chimiques des groupes SCN dans les composés de coordination du type Cu(SCN)₂L₂ (L=2-, 3 et 4-picoline, 2,3-, 2,4-,2,5-, 2,6-, 3,4- et 3,6-lutidine). L'effet le plus prononcé du groupe CH₃ s'observe en position 4. Cette influence du groupe méthyle sur le degré des changements chimiques indique aussi l'influence mutuelle des ligands dans les composés de coordination du Cu(II).

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- , , NCS Cu(NCS)₂,L₂, L=2-, 3- 4- , 2.3-, 2.4-, 2.5-, 2.6-, 3.4- 3.5-. , 4. Cu(II).

     

Geometrical structure of yttrium and metal-bromine complexes in solution: limitations of extended X-ray absorption fine structure analysis (EXAFS)

An extensive study on the appearance of multi-electron features in the X-ray absorption spectra of several yttrium(III)-based compounds has been performed. The existence of a multi-electron transition of non-negligible intensity within the extended X-ray absorption fine structure (EXAFS) region of the Y K-edge spectra has been proven. The impact of such features in the EXAFS analysis is made evident for aqueous solutions of YBr3 x 6H2O in liquid and glassy states in the concentration range 0.005-2.0 M, in which this transition induces an overestimation in the coordination numbers derived from EXAFS. We have performed theoretical computation of cross-sections for the double-electron processes at the K-edge of both Y and Br. These computations have been applied to the experimental EXAFS K-edge spectra of both Y and Br in several solids and in aqueous solutions. While in the case of Y K-edge spectra the presence of such multi-electron transitions was seen to seriously affect the standard EXAFS analysis, its influence in the case of Br K-edge spectra was determined to be negligible.     

Reactions of pyrrolidine enamines of cyclic and acyclic 3,4-dioxobutanoic acid Derivatives with dimethyl acetylenedicarboxylate. A new case of atropoisomerism.

Reaction conditions and structure of the starting enamines (cyclic or open-chain) determine greatly the final products of the title reactions. Whereas in benzene and acetonitrile, DMAD and 1 give a mixture of the diastereoisomeric dienamines 5, in methanol they afford pirrolizine 3. Enaminofuranones 2 and 10 furnish the corresponding “Michael adducts” 7a,b,c and 11a,b,c but fail to yield pirrolizines. It has been demonstrated that above b and c adducts differ exclusively on the arrangement of groups around a chiral axis.     

Nachweis isomerer Phenole und Nitroaniline,von Naphthylamin und Anilin

Zusammenfassung Die mit diazotiertem p-Nitranilin hergestellten Tetrazoverbindungen von Phenolderivaten geben mit Magnesium in alkalischem Mediumfarbige Komplexe. Die Farbe des Komplexes ist verschieden bei substituierten und nicht substituierten bzw. verschieden substituierten Phenolen. Damit kann man Phenol-, Kresol- und Chlorphenol-Isomere bzw. 2,4- und 2,6-Dichlorphenol unterscheiden.Beim Diazotieren von Nitranilin und Kuppeln mit Anilin entstehen. Indikatorsäuren; p-Nitranilin bildet die stärkste Indikatorsäure, m-Nitranilin die schwächste. Auf dieser Grundlage können alle drei Isomeren nebeneinander nachgewiesen werden. Außerdem bilden die aus p- und o-Nitranilin entstandenen Indikatoren mit Magnesium verschieden gefärbte Nitronsäurekomplexe, während m-Nitranilin, das zur Nitronsäuretautomerie nicht befähigt ist, keinen Komplex bildet.Naphthylamine geben mit diazotiertem p-Nitranilin in wäßrigem. Medium eine Indikatorbase, Anilin eine Indikatorsäure. In alkoholischem Medium führt-Naphthylamin bei Kupplung von diazotiertem p-Nitranilin zu einem amphoteren Säure-Base-Indikator, aber-Naphthylamin und Anilin zu Indikatorsäuren. Damit kann man Naphthylamin und Anilin nebeneinander nachweisen. Kuppelt man Phenyldiazoniumchlorid mit Naphthylamin, so erhält man mit-Naphthylamin eine starke Indikatorbase, mit- Naphthylamin eine schwache Indikatorbase. Auf der Basis dieser Indikatorwirkung kann man-Naphthylamin neben- Naphthylamin nachweisen.

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Summary The tetrazo compounds of phenol derivatives prepared with diazotizedp-nitraniline yield colored complexes with magnesium in alkaline surroundings. The color of the complexes differs with substituted and non-substituted or variously substituted phenols. It is possible in this way to differentiate phenol, cresol and chlorophenol isomers, and also 2,4- and 2,6-dichlorophenol.Indicator acids result from diazotized nitraniline coupled with aniline;p-nitraniline yields the strongest indicator acid,m-nitraniline the weakest. With this information as a basis, all three isomers can be detected in the presence of each other. In addition, the indicators produced fromp- ando-nitraniline give nitronic acid complexes with magnesium that differ in color, whilem-nitraniline, which is not capable of nitronic acid tautomerism, forms no complex.Naphthylamines gives an indicator base in aqueous medium with diazotizedp-nitraniline, whereas aniline yields an indicator acid. In alcoholic medium, 1-naphthylamine on coupling with diazotizedp-nitraniline produces an amphoteric acid-base indicator, but 2-naphthylamine and aniline yield indicator acids. Naphthylamine and aniline can be detected in this way in the presence of each other. If phenyldiazonium chloride is coupled with naphthylamine, a strong indicator base is obtained with 1-naphthylamine, a weak indicator base with 2-naphthylamine. This indicator action is the basis of the detection of 1-naphthylamine in the presence of 2-naphthylamine.

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Résumé Les composés tétrazoïques des dérivés phénoliques qui se forment avec lap-nitraniline diazotée, donnent avec le magnésium, en milieu alcalin, des complexes colorés. La couleur du complexe diffère suivant que les phénols sont substitués, non substitués ou différemment substitués. On peut ainsi distinguer le phénol, les crésols et les chlorophénols isomères, ainsi que les dichloro-2,4 et -2,6 phénols.En diazotant la nitraniline et en copulant avec l'aniline, des acides indicateurs prennent naissance, lap-nitraniline donnant l'acide indicateur le plus fort, lam-nitraniline le plus faible. En s'appuyant sur ce fait, on peut rechercher les trois isomères en présence les uns des autres. En outre, les indicateurs qui prennent naissance à partir de lap- et de l'o-nitraniline forment avec le magnésium différents complexes colorés acinitrés, alors que lam-nitraniline, qui n'est pas susceptible d'une tautomérie de l'acide nitronique, ne donne pas de complexe.Les naphtylamines donnent avec lap-nitraniline diazotée, en milieu aqueux, une base indicateur et l'aniline, un acide indicateur. En milieu alcoolique, l'-naphtylamine conduit par copulation de lap-nitraniline diazotée à un indicateur acide-base amphotère mais la-naphtylamine et l'aniline à des acides indicateurs. On peut ainsi rechercher la naphtylamine et l'aniline en présence l'une de l'autre. Si l'on copule le chlorure de phenyldiazonium avec la naphtylamine, on obtient avec la forme une base indicateur forte et avec la forme une base indicateur faible. En se fondant sur cette action d'indicateur, on peut rechercher l'-naphtylamine en présence de-naphtylamine.

     

Etude de la chloration du polychlorure de vinyle en fonction de sa tacticite

Polyvinyl chloride samples of various tacticity have been prepared and photochlorinated in CCl₄ for 4 hr. The chlorination degree correlates directly with the degree of syndiotacticity. Initial PVC with syndiotacticity about 56 per cent, which can be regarded as alternate sequences of syndiotactic and isotactic diads, is quickly chlorinated. The mechanism of chlorine attack on the macromolecula is directly connected with the stereoregularity.     

Sandwich structures at oil-water interfaces under alkaline conditions

Equilibrium liquid crystal (LC) layer on an interface between crude oils and water was observed at high pH. This layer is composed mainly of sodium naphthenates produced in situ at the water/oil interface. Transient LC layer was also evolved at the interface of aqueous phase of sodium hydroxide solutions and oleic phase of naphthenic acid (NA) solutions as result of a chemical reaction between NaOH and NA. This chemical reaction causes transport process resulting in a disturbance of the interface. Optical observation of this interface disturbance reviled that the interface covered with LC shows considerably lower flexibility as compared to LC free interface. The LC layer eventually dissolves in the water phase at low oil-to-water ratio, while at high oil-to-water ratio it can form an equilibrium phase, which spreads spontaneously at the oil-water interface.     

Thermodynamic parameters for the molecular inclusion reaction of dulcin with beta-cyclodextrin. spectrofluorimetric determination of dulcin

The inclusion of dulcin in alpha- and beta-cyclodextrin has been studied by fluorescence spectroscopy. To quantitatively describe complex formation between the beta-cyclodextrin and dulcin, an association constant of 290 M(-1) at 21 degrees was obtained. The thermodynamics associated with the complex formation between dulcin and beta-cyclodextrin in aqueous solution has been studied. The obtained value of DeltaG(0) = -13.7 kJ/mole at 21 degrees , together with DeltaH(0) = -33.6 +/- 2.3 kJ/mole and DeltaS(0) = -67.2 +/-8.3 Jmole(-1) K(-1) indicate that dulcin has a very marked tendency to associate with beta-cyclodextrin in water. The inclusion complex of dulcin in beta-cyclodextrin has been used to determine dulein in the range 0.13-5 mug/ml the method has been applied to determine dulcin in soft drinks.     

Analysis of primary aliphatic short-chain monoamines by LC in water samples

Several derivatization procedures with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) were compared for a rapid analysis of primary aliphatic short-chain monoamines in water samples by HPLC using a LiChorospher analytical separation column (100RP₁₈ mm i.d., 5 μm). Both the solution and the solid-support assisted off-line derivatization on C₁₈ SPE cartridges were inadequate options because of beginning degradation processes of the instable isoindol derivatives during their transfer to the analytical column. This problem was precluded with the on-column or solid-support assisted on-line derivatization. In the last mentioned procedure, the derivatization took place in a Hypersil C₁₈ precolumn ( mm i.d., 30 μm) connected with an additional preconcentration step resulting in better detection limits (0.002-0.040 μg ml⁻¹ requiring only 150 μl of water sample) than in the on-column procedure (0.08-0.16 μg ml⁻¹). The improved sample handling, the better control of parameters affecting reaction rates, the fully automation of this method with only 10 min analysis time for each sample are further advantageous. The potential of the solid-support assisted on-line derivatization was outlined and applied to water samples from several sources. Recovery values near 100% were obtained.     

Properties and analytical applications of the heteropolymolybdates of phosphorus, arsenic, silicon and germanium-IV Determination of phosphomolybdic and silicomolybdic acids via the molybdenum content, with phenylfluorone

Procedures are proposed for the determination of phosphorus and silicon in the ppM range, by extraction of phosphomolybdic and silicomolybdic acids with organic solvent, decomposition of the complex and spectrophotometric determination of its molybdenum content.