Monomeric copper(II) and nickel(II) complexes of N,N,N′,N′-tetrakis [(2-benzimidazolyl)methyl]-1,2-cyclohexanediamine], a chelating ligand containing imidazole groups

Summary Cu^II and Ni^II coordination compounds with N,N,N,N-tetrakis[(2-benzimidazolyl)methyl]-1,2-cyclohexanediamine (CDTB) have been prepared and characterized. The crystal structure of [Cu(CDTB)](ClO₄)₂ has been determined. The geometry around the Cu atom is highly irregular and can best be described as a cis-distorted octahedron, with four short CuN bond distances of 1.988(3) Å and 2.028(3) Å, and two very long CuN bond lengths of 2.543(4) A. The cis NCuN chelate angles in the complex range from 68.8(2) for N(1)CuN(1) to 141.03° for N(4)CuN(1). The cyclic voltammogram of the complex shows a fully reversible one-electron redox wave at E _1/2 = 0.162V versus standard calomel electrode, corresponding to the Cu^I/II redox couple. The structure of [Ni(CDTB)](NO₃)₂ ·EtOH has also been determined. The geometry around the Ni atom in this compound can be described as distorted octahedral, with N(4), N(4), N(1), N(1) as the ligating atoms in the basal plane, with cis chelate angles ranging from 79.37(10) to 120.9(2)° with the trans N(2)NiN(2) angle at 175.1(2)°. The structural differences in these two compounds are undoubtedly electronic rather than steric.     

Electrochemical studies of bimetallic rhenium(III) complexes possessing two accessible mixed-valence states

Summary Bimetallic complexes of the general formula [Cl₃(PPh₃)₂Re^III(NCArCN)Re^III(PPh₃)₂Cl₃] (where NCArCN represents an aromatic dinitrile) have been prepared and their solution phase electrochemistry examined. Each of these complexes undergoes two one-electron metal-centred oxidations. The potential difference between these oxidations gives a measure of the stability of the Re^III/Re^IV mixed-valence state toward disproportionation, and ranges from <0.050 V in the most weakly coupled system (4,4-biphenyldicarbonitrile bridge) to ca. 0.200 V for the most strongly interacting metal centres (9,10-dicyanoanthracene bridge). Likewise, all of the complexes show two one-electron transfers in either simultaneous or sequential fashion depending on the nature of the bridge.     

Influence of heme periphery on the electronic structure and Mössbauer parameters of hemoglobin

For the five-coordinated complexes of ferroprotoporphynynn with imidazole, a quantum-chemical analysis of the electronic structure and Mossbauer spectral parameters has been canied out. Peripheral substituents (CH3, Cf13, C₂H₄COOH) were introduced into the porphynin macrocycle to model the real chemical structure of protopo'phynynn in the heme group of desoxyhemoglobin. The calculations have shown that near the occupation border in the complaes there are MO which are due to the -systems of the CH= CM₂ and CH₂CH₂COOH substituents. The orientalion of the vinyl fragments has a considerable effect on the populations of the Fe d-orbitals and the quadrupole splitting E_Q for the⁵B₁ and⁵B₂ terns.Institute of Biophysics, Ministry of Health, Russian Federation. Translated fromZhurnal Strukturmoi Khimii, Vol. 34, No. 5, pp. 90–93, September–October, 1993.Translated by L. Smolina     

Comparison of methods of determining Arrhenius equation parameters by the least squares method

The parameters of the Arrhenius equation determined by the linear, weighted linear and non-linear least squares methods and by the simplex method are compared. Since the non-linear least squares method permits the consideration of statistical weights of both the dependent (k) and independent (T) variables and does not involve logarithmic transformation, it is advisable to calculate the parameters of the Arrhenius equation by means of the non-linear least squares method.

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Zusammenfassung Arrhenius-Parameter bestimmt nach der linearen, mit Gewichten operierenden linearen und nicht-linearen Methode der kleinsten Fehlerquadrate oder nach der Simplex-Methode werden miteinander verglichen. Da bei der nicht-linearen Methode der kleinsten Fehlerquadrate sowohl die abhÄngige (K) als auch die unabhÄngige (T) Variable mit statistischen Gewichten versehen werden kann und keine logarithmische Transformation vorgenommen wird, ist es zweckmÄ\ig, die Berechnung der Parameter der Arrhenius-Gleichung nach der nicht-linearen Methode der kleinsten Fehlerquadrate auszuführen.

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, , . , k, T, , .

     

Changes of acidity and catalytic properties of ammonium sulfate-titanium oxide on thermal treatment

In this paper changes of acidity and catalytic properties of ammonium sulfate-titanium oxide with the treatment temperature at 423–773 K have been investigated.

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- 423–773 .

     

Oxidizing properties of alumina towards alcohols. Possible reaction scheme

By chemical trapping, an acyl species has been evidenced in the oxidation of alcohols to carboxylate on an alumina surface. A possible reacton scheme is discussed.

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. .

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

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, - , , () . .

     

Catalytic activity of honeycomb catalysts, I. The benzene-cyclohexane (de)hydrogenation reaction

Monolithic supported platinum catalysts were investigated with respect to their hydrogenation and dehydrogenation activity towards benzene and cyclohexane, respectively, between 250° and 350°C. Conversion of benzene to cyclohexane is optimal for the volume ratio H₂/Bz=5 at lower temperatures. In the cyclohexane dehydrogenation reaction, high temperatures, associated with lower N₂/Cy ratios, are beneficial. No byproducts were observed in the two reactions.

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, , 250 °C 350 °C. H₂/=5. N₂/ . .

     

Investigation of surface phenomena on solid catalysts by simultaneous thermogravimetry and DTA

Thermogravimetry and simultaneous DTA were used to investigate the phenomena of adsorption, desorption and surface reactions on solid catalysts. The measurements were carried out with NaX and X-type ion-exchanged zeolites and silica-alumina gels (Ketjen) treated with sodium hydroxide in the presence of carbon dioxide. On the basis of the quantitative results it is possible to give an interpretation of the surface phenomena and to establish the existence of various active centres on the surfaces of the catalysts. In the case of the adsorption of carbon dioxide on X-type zeolites, the quantity of carbon dioxide adsorbed is much smaller on ion-exchanged zeolites than on NaX.

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Zusammenfassung Thermogravimetrie und simultane DTA wurden zur Untersuchung der Adsorptions-, Desorptions-Erscheinungen und Oberflächenreaktionen an festen Katalysatoren eingesetzt. Die Messungen wurden and NaX und Zeolithen des Typs X sowie an Silika-Aluminiumoxidgelen Ketjen durchgeführt, welche mit Natriumhydroxid in Gegenwart von Kohlendioxid behandelt worden waren. Aufgrund der quantitativen Ergebnisse ist es möglich eine Deutung der Oberfiächenerscheinungen zu geben und die Existenz verschiedener aktiver Zentren an der Katalysatorenoberfläche nachzuweisen. Im Falle der Adsorption von Kohlendioxid an Zeolithen des Typs X ist die Menge des adsorbierten Kohlendioxids am Ionenaustauscher viel niedriger als am NaX.

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Résumé Application de la TG et de l'ATD simultanées à l'étude des phénomènes d'adsorption, de désorption et de réactions de surface sur des catalyseurs solides. Les mesures ont été effectuées avec des zéolites échangeuses d'ions de type NaX et X ainsi qu'avec des gels Ketjen silice-alumine traités par NaOH en présence de CO₂. Les résultats quantitatifs permettent de donner une interprétation des phénomènes de surface et d'établir l'existence de divers centres actifs à la surface des catalyseurs. Dans le cas de l'adsorption de CO₂ sur les zéolites de type X, la quantité de CO₂ adsorbé est beaucoup plus faible que sur les zéolites de type NaX.

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DTA , . - NaX X - « », . . X, - , NaX.

     

GC-MS Investigation of Hexamethyldisiloxane-Oxygen Fed Plasmas

This paper deals with the determination of by-products formed in plasmas fed with hexamethyldisiloxane (HMDSO), oxygen, and Ar. The gas effluent has been sampled by means of a cold trap and analyzed using gas chromatography-mass spectrometry. The results indicate that under the experimental conditions utilized, HMDSO is not activated by reactions with oxygen but mainly by electron collisions. Oxygen controls the overall chemistry of the plasma since it influences the quali-quantitative distribution of by-products. Many linear and cyclic oligomers have been observed and most of them contained one or moreMe₂SiO groups. The concentration of detected by-products, except trimethylsilylformate, decreases with O₂ addition.     

An implicit heating programme to minimize the effect of the difference between the sample temperature and the programmed temperature

An implicit heating programme is suggested for minimization of the effect of the difference between the sample temperature and the programmed temperature in a thermoanalytical set-up.

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Zusammenfassung Es wird ein implizites Aufheizprogramm beschrieben, das den Einfluss des Unterschiedes zwischen Probentemperatur und programmierter Temperatur für die Probe minimalisiert.

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.

     

Polymeric membrane sodium-selective electrodes based on calix[4]arene ionophores

Six kinds of tetra alkylester type calix[4]arene derivatives, (R₁=R₂=CH₃1, C₂H₅2, C₃H₇3,n-C₄H₉4,t-C₄H₉5,n-C₁₀H₂₁6), a diethyl-didecyl mixed ester type (R₁=C₂H₅, R₂ =C₁₀H₂₁7), and three kinds of lower rim bridged types (R₁=C₂H₅, R₂–R₂=(CH₂)₁₀8, (CH₂)₁₂9, (CH₂)₂(OCH₂CH₂)₃10) were characterized by electrochemical measurement to elucidate the effect of the length of the alkyl group of alkoxycarbonyl substituents on Na⁺ selectivity. To obtain excellent Na⁺ selective ionophores, introduction of short chain alkyl groups rather than long chain ones, such as a decyl group, and maintenance of sufficient solubility of the calix[4]arene derivatives in the membrane solvent are required concurrently. Among the calix[4]arenes tested, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-tert-butylcalix[4]arene2, and the diethyl-didecyl mixed ester type derivative7 are the best ionophores for a Na⁺ selective electrode. On the other hand, sodium selectivity of the bridged type derivative9 is comparable or even superior to that of the known bis(12-crown-4).This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Rate constants for photochemically induced hydrogen abstraction calculated from spin trapping rates

ESR spin trapping method has been applied to calculate the rate constant for -hydrogen abstraction from ethylbenzene by triplet anthraquinone: k₁=1.1×10⁷ M^–1 s^–1 (error of estimation 25%).

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( ) -CH : k₁=1.1×10⁷ M^–1–1 ( 25%)

     

Calorimetric studies of alumosilicate catalysts I. Heat and entropy of cumene adsorption on Mg-metakaolinite at small surface coverages

Differential heats of cumene adsorption at 293 K on Mg-metakaolinite at surface coverages =0.005–0.10 have been measured on a Calvet microcalorimeter. The adsorption heat decreases drastically from 71 to 59 kJ/mol with changing the adsorption from 0.02 to 0.06 mol/m². The presence of two energetically different types of adsorption centers is predicted on the Mg-metakaolinite surface.

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293 Mg- =0,005–0,10. 71 59 / 0,02 0,06 /². Mg-.

     

Thermal decomposition kinetics of sodium metaperiodate

Aged and fresh samples of sodium metaperiodate are subjected to thermal decomposition studies in air by TG, DTG and DTA techniques. The kinetic parameters for their decomposition have been evaluated by weighted least squares method using equations of Coats-Redfern, Horowitz-Metzger and Freeman-Carroll. The results indicate that, within the limits of experimental error, ageing did not change the E^* values considerably.

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, . , -, - -. , , , E^*.

     

Platinum-palladium catalysts for hydrogen fuel cell electrodes

Five series of Pt–Pd/C catalysts were prepared with different total metal loading and different atomic composition in Pt and Pd. The activity in electrooxidation of hydrogen were measured for all these catalysts. Electrooxidation of hydrogen is a structure insensitive reaction on platinum and a structure sensitive reaction on palladium. For bimetallic catalysts, curves of activity as a function of the composition of the catalyst can exhibit a maximum. Yet, metal loading can alter the atomic composition at which activities are maxima.

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Pt–Pd/C Pt Pd. . - - . . , .

     

Influence of mechanical activation on decomposition of a chalcopyrite-pyrite mixture in an oxidizing atmosphere

The influence of the addition of pyrite and mechanical activation on an oxidative decomposition of chalcopyrite was studied. The course of the thermoanalytical curves and X-ray identification of the products showed that addition of pyrite affects mainly the endothermic processes taking place in region of low temperatures but does not significantly influence the temperature of CuSO₄ formation and its content in the products of decomposition. Changes in fine and superfine structure of chalcopyrite brought about by mechanical activation at grinding cause the complex of exothermic oxidative reactions to proceed at temperatures as much as 180 deg lower than for a non activated sample. The endothermic effect of these oxidation reactions become more marked and the proportion of CuSO₄ in the products of the oxidative decomposition increases significantly.

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Zusammenfassung Am oxidativen Zerfall von Chalkopyrit wurde der Einfluss der Zugabe von Pyrit sowie der mechanischen Aktivierung untersucht. Der Verlauf der thermoanalytischen Kurven und Röntgendiffraktionsanalyse der Produkte zeigten, dass die Zugabe von Pyrit hauptsächlich die sich bei niedrigeren Temperaturen abspielenden endothermen Prozesse beeinflusst, nicht aber die Bildungstemperatur von CuSO₄ sowie dessen Gehalt in den Zersetzungsprodukten. Durch mechanisches Aktivieren mittels Feinmahlen hervorgerufene Veränderungen in der Fein- und Superfeinstruktur lassen die Gesamtheit der exothermen oxidativen Reaktionen bei Temperaturen ablaufen, die etwa 180 Grad unterhalb derer für unaktivierte Proben liegen. Die endotherme Färbung dieser Oxidation wird eindeutiger und der Anteil von CuSO₄ in den Produkten des oxidativen Zerfalles nimmt eindeutig zu.

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. , . , , - , 180° , . - .

     

Synthesis of light alcohols from carbon monoxide and hydrogen over copper-iron catalysts

The activity and selectivity of copper-iron catalysts for the synthesis of light alcohols from carbon monoxide and hydrogen were studied. The suitable ratio of copper to iron and optimal chemical composition of the catalyst were determined.

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- . .

     

Estimation of kinetic parameters in oxidative dehydrogenation of n-butenes over SnO2?Sb2O4 catalysts

Kinetic curves measured in the oxidation of n-butenes over a SnSb=31 mixed oxide catalyst were fitted by the kinetic model put forward in a previous paper. The goodness of fitting shows that the kinetic behavior of this complex reaction system can be described by a mechanism involving acidic and redox sites on the catalyst surface.

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- SnSb=31 , . , , - .