Octahedral ruthenium(II) alkenyl complexes containing {\text{N}}{\text{S}} coordinated heterocyclic ligands

Summary Hexacoordinated ruthenium(II) alkenyl complexes of the type Ru(CO)(CR=CHPh)( )(PPh₃)₂ have been prepared from coordinately unsaturated -vinyl complexes [Ru(CO)Cl(CR=CHPh)(PPh₃)₂] (R = H or Ph) and the sodio-derivative of the containing heterocyclic ligands [ = 3,4-substituted 1,2,4-triazole-5-thione and 5-alkylthio-1,3,4-thiadiazole-2-thione] in a CH₂Cl₂/MeOH mixture at ambient temperature. The complexes were characterized by their elemental analysis, i.r., ¹H and ³¹P n.m.r. spectra. An octahedral structure with transphosphorus ligands has been assigned on the basis of the spectral data.     

Effect of solvent on the partial molal volumes and heat capacities of nonelectrolytes

Group contributions to in seven solvents and to in three solvents have been tabulated. The variation of group parameters is discussed in terms of the solvent compressibility coefficient, _T. The scaled particle theory (SPT) is used to calculate cavity contributions to and C _p2 ^o . Interaction contributions are obtained from the cavity terms and and values estimated through the additivity schemes. values are more sensitive to solute-solvent interactions than in water and less sensitive in methanol. The SPT results for heat capacities support the concept of structural promotion by hydrophobic solutes in water.     

A method for experimental determination of effective resonance energies related to (n, γ) reactions

When making use of some single comparator or absolute standardization methods in reactor neutron and in epicadmium neutron activation analysis, the knowledge of the effective resonance energy ( ) is essential to correct for the effect of the nonideal epithermal flux distribution on the analysis result. can be calculated from neutron resonance data, but when these are incomplete, not accurate or even not known at all, experimental determination should be considered. Such a method, providing both and the resonance integral to 2200 ms^–1 cross-section ratio (Q_O), is described in this paper. Results are given for 11 isotopes.     

Some analytical results forABC,ABCD, andXBCD coupled spin 1/2 systems. II

In the preceding paper, it was shown that the calculation of the density matrix(t) for multiply connectedABC, etc., spin 1/2 spin systems can be greatly simplified by subdividing the Hamiltonian into , where is a suitable linear combination of the constants of the motion. In this paper, a framework for the determination of the time evolution of high-order multipolar quantum states is presented and discussed. It is shown that the necessary mathematical labour is reduced to a minimum by (i) exploiting the fact that is a good quantum number, and (ii) using the theory of partitioned matrices. For example, it is shown that for a generaln-coupled spin 1/2 system, the spin dynamics of the multipolar states, whereK _max is the maximum tensorial rank, can be determined without the need to diagonalize the full 2 ⁿ × 2 ⁿ Hamiltonian matrix, wheren is the number of spins. In fact, to describe the time evolution of the multipolar states it is only necessary to diagonalize twon ×n matrices at most. Finally, some cautionary remarks are made concerning the use of the weak-coupling approximation.     

Glass transitions in crosslinked epoxy networks

Epoxy resins of DGEBA type were thermally cured with diaminodiphenylmethane as crosslinking agent, and then analysed by Differential Scanning calorimetry (DSC) at various heating rates in order to determine the glass transition temperatureT _g of the final networks. First it was shown that during cyclingT _g is shifted towards higher values up to a maximum or . Such a change is attributed to an increasing extent of cure which develops during the thermal analysis, and also to relaxation processes thermally activated inside the polymeric matrix. Then the dependence of on the heating rateq imposed by the DSC apparatus was presented forq changing from 0.1 to10C min^–1. At heating rates exceeding 3C min^–1 only the classical temperatureT _g was detected, but at smallerq values, an additional endothermic transition was revealed, located at higher temperature and linked to a physical aging-like phenomenon, which takes place at low heating rates. The plot of against logq is divided into two quasi-linear parts on each side ofq=3C min^–1. In conclusions, an equation was given to describe the vs. logq function.     

Formamidines and triazenes as precursors for the preparation of rhenium imido-complexes

Summary The rhenium(V) imido-complexes [Re(NR)Cl₃(PPh₃)₂] have been obtained by heating the rhenium(V) derivative [ReOCl₃(PPh₃)₂] with RNHCHNR R = Ph (1a), p-MeC₆H₄ (1b), p-ClC₆H₄ (1c) andp-FC₆H₄ (1d) in THF under reflux. [Re(NR)Cl₃(PPh₃)₂] (R =p-MeQ₆H₄) has also been obtained by heating the rhenium(III)-triazenido complex [ReCl₂(RN N NR)(PPh₃)₂] in CCl₄ under reflux.     

Reaction graphs and a construction of reaction networks

Summary A general definition of reaction graphs is presented. For a pair of isomeric molecular graphs and , related by a chemical transformation , the reaction graph is determined using a maximal common subgraph defined for vertex mapping . A binary operation defined for graphs constructed over the same vertex set enables us to decompose the reaction graph into the sum of prototype reaction graphs. A decomposition of an overall reaction graph can be advantageously used for the construction of a reaction network. An oriented path in this network beginning at and ending at corresponds to a breakdown of the transformation into a sequence of intermediates.     

1H and 13C NMR spectra,isomers, and imine-enamine tautomers of N-(1,2,5-trimethyl-4-piperidylidene)aniline

The product of condensing 1,2,5-trimethylpiperidin-4-one with aniline has been investigated by NMR spectroscopy. Three isomers of N-(1,2,5-trimethyl-4-piperidylidene)aniline have been identified differing in the configuration of the methyl groups at C₂ and C₅ of the piperidine ring and the Z,E isomerism about the C=N bond. Traces of the enamine tautomeric form of the imine were also detected. , , and spin-spin couplings were used to determine the structural configuration of the isomers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1405–1408, October, 1989.     

On chemical bonding between molecular fragments. Closed-shell fragments

The chemical bonding between two closed-shell molecular fragments has been analyzed in terms of comparison of the antisymmetrized product of wave functions of the fragments with the wave function of a molecule composed of these fragments ^M . As a measure of the fragments' electronic structure variation upon molecule formation we took the cosine of the angles between ^M and in Hilbert space, as well as between the corresponding first-order density matrices ^M and . As an example, compounds of the type BH₃L (L=CO, NH₃, PH₃, H₂O, PF₃) have been considered. It is stressed that a necessary condition of chemical bonding between closed-shell fragments is the contribution of vacant orbitals of fragments into the bond.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 34, No. 3, pp. 3–8, May–June, 1993.Translated by L. Smolina     

Observedtrans influence of donor atoms in monocharged bidentate ligands: Crystal structure of the acetone solvate of 2-carboxyquinolinatocarbonyltriphenylphosphinerhodium(I)

Summary 2-Carboxyquinolinatocarbonyltriphenylphosphinerhodium(I), [Rh(Quin)(CO)(PPh₃)], was prepared by replacement of CO by PPh₃ in the corresponding dicarbonyl. The compound crystallizes in the triclinic space group Åb=17.168(6) Å,c=9.254(5) Å, =101.49(5)°, =95.74(4)°, =98.41(4)°, d_cxp=1.45g cm^–3 and Z=2. The crystal structure was dermined from 3496 observed reflections. The final R value was 0.061. This structure determination indicates that the nitrogen atom of the chelate ring has the largesttrans influence since the carbonyl grouptrans to this atom was substituted by the PPh₃ ligand. The effects of different donor atoms in bidentate ligands, as well as the ring size of the chelate ring, on the relativetrans influence of the donor atoms are discussed.     

The partial molal volume and compressibility change for the formation of the calcium sulfate ion pair at 25°C

The apparent molal volumes (_v) and compressibilities (_K) of CaSO₄ solutions have been determined at 25°C from precise density and sound-speed measurements. The large deviations of the values of _v and _K from the limiting law and various additivity estimates for the free ions (Ca²⁺, SO ₄ ^2– ) have been used to estimate the partial molal volume ( ) and compressibility ( ) for the formation of the CaSO ₄ ⁰ ion pair. Values of = 25 ± 3 cm³-mole^–1 and = (54±21)×10^–4 cm³-mole^–1-bar^–1 were found. Since these values are larger than the value for the formation of MgSO ₄ ⁰ , the results indicate that more inner-sphere ion pairs are formed when SO ₄ ^2– complexes with Ca²⁺ than with Mg²⁺. Using a simple model for ion-water interactions, the percent of inner-sphere or contact ion pairs in CaSO₄ solutions is estimated to be 36 to 37%.     

First and second thermodynamic mixing functions of ethylbenzene+n-nonane, +n-decane,and+n-dodecane at 25 and 45°C

Isothermal compressibilities _T and isobaric thermal expansion coefficients _p have been determined for mixtures of ethylbenzene+n-nonane, +n-decane, and +n-dodecane at 25 and 45°C in the whole range of composition. The excess functions and have been obtained at each measured mole fraction. The first one is zero for ethylbenzene +n-nonane, positive for ethylbenzene +n-decane, and +n-dodecane and increases with chain length n of the n-alkane. The function is positive for the three studied systems and nearly constant with n. Both mixing functions increase slightly with temperature. From this measurement and supplementary literature data of molar heat capacities at constant pressure C _P , the isentropic compressibilities _S, the molar heat capacities at constant volume C _V and the corresponding mixing functions have been calculated at 25°C. Furthermore, the pressure dependence of excess enthalpy H ^B , at zero pressure and at 25°C has been obtained from our experimental results of and experimental literature values for excess volume V ^E .     

Preferential solvation in three component systems: Evaluation of Kirkwood-Buff parameters

The extent of local excess or deficiency of a component solvent near the solute in a mixed binary solvent has been calculated using the Hall formalism for the Kirkwood-Buff equation. The possibility of calculation of the two solute-solvent Kirkwood-Buff parameters using the values is discussed. A model calculation using literature data for preferential solvation in mixed binary solvents is presented. The solute-solvent and solvent-solvent interactions and the relative size of the solvents are also shown to be relevant factors in determining the values.     

Mass transfer in shell-core inorganic TIP1 ion exchanger

The ion exchange processes of (OAc^–) and (OAc^–) proceeding in shell-core inorganic ion exchanger Ti (HPO₄)₂·1/2H₂O has been studied and the diffusion equation whose boundary conditions are satisfied by a shell-core model was solved. Based on the equation solved and experimental data, the diffusion coefficients corresponding to the exchange process (OAc^–) and Li⁺–H⁺ (OAc^–) at 17°C are found to be 7.7×10^–9 and 6.2×10^–8 cm² s^–1 and the activation energies 3.4×10⁴ and 5.0×10³ J mol^–1, respectively. Compared to the gel type of styrene-divinylbenzene strong acid exchanger with 20% cross linking, it can be concluded that the rate of or exchange is 3.5 times faster than that in the organic exchanger.TIP was obtained from the Salt Lake Institute of the Academy of Science of China.     

Electronic spectrum of dibiphenylene-ethene radical anion

The electronic absorption spectrum for the dibiphenylene-ethene radical anion ( ), generated electrochemically in dimethylsulfoxide solutions, is reported. Based on calculations by the LCAO-MO method in theHückel approximation and on the analysis of the band positions it is suggested that in the molecule two planar fluorenylidene fragments are twisted (60°) about the central C=C bond.

---

Das Elektronenabsorptionsspektrum des Dibiphenylen-Radikalanions (Kurze Mitteilung)

Zusammenfassung Das Dibiphenylenethen-Radikalanion ( ) wurde elektrochemisch hergestellt und das Elektronenabsorptionsspektrum aufgenommen. Auf Grund von LCAO-MO Berechnungen in derHückel-Annäherung und der Analyse der Bandenlagen wird nahegelegt, daß im -Molekül zwei planare Fluorenyliden-Fragmente ca. 60° um die zentrale C=C-Bindung verdrillt angeordnet sind.

     

Nouvelle méthode de linéarisation de la relationT_{Fi} = f(1/Fi) en microcalorimétrie différentielle

Résumé Après une revue des méthodes utilisées pour linéariser la relation lors des déterminations de pureté par micro-calorimétrie différentielle, une nouvelle méthode, non itérative est décrite et discutée.

---

A new method of linearization of the plot for the differential scanning calorimetry

Summary A critical review of the plot linearization methods in purity determinations by differential scanning calorimetry is presented. A new, non iterative, linearization method is described and discussed.

---

Zusammenfassung Nach einer Übersicht der üblichen Methoden der Linearisierung der Beziehung für die Reinheitsbestimmung mittels Differentialmikrocalorimetrie wird eine neue, nicht iterative Methode beschrieben und diskutiert.

     

Thermodynamic data for nonmesomorphic solutes at infinite dilution in the nematic and isotropic phases of hexylcyanobiphenyl

Infinite dilution solute activity coefficients _o ² , partial molar excess enthalpies and entropies , and partial molar enthalpies ( ) and entropies ( ) of solution, obtained using gas-liquid chromatography (GLC), are reported for thirty nonmesomorphic solutes in the nematic and isotropic phases of p-n-hexyl-p-cyanobiphenyl (6CB). The solutes studied include normal and branched alkanes, alkenes and hexadienes (with some cis and trans isomers), and benzene. The results corroborate earlier studies on other members of the p-n-alkyl-p-cyanobiphenyl homologous series of liquid crystals. The results demonstrate the effect that solute structure (size, shape, flexibility, polarizability and polarity) has on the solution process. Thermodynamic data for the cis and trans isomers of 2-pentene and 2-hexene are examined. A method for the simultaneous examination of the effects of both solute and solvent structures on the solution process is suggested.     

Phase behavior of ethylene oxide-dimethylsiloxane PEO-PDMS-PEO triblock copolymers with water

Linear ethylene oxide-dimethylsiloxane PEO-PDMS-PEO triblock copolymers have been synthesized by hydrosilation of ,-dihydropoly(dimethylsiloxane) ) and -methyl--propargylpoly(ethylene oxide) . Studies by optical microscopy, complementary small-angle x-ray scattering (SAXS), and differential scanning calorimetry (DSC) have shown that the copolymers mixed with water are characterized by lyotropic liquid crystalline phases according to composition and temperature. The binary phase diagrams with varying copolymer composition are reported.     

A generalized separation reaction scheme for assessment of the radioanalytical method of concentration dependent distribution

For the assessment of the analytical error of concentration dependent distribution (CDD), complex-forming separation reaction was proposed in a generalized form of equilibrium , where n is the effective stoichiometric coefficient, i.e. the difference of mean ligand numbers and <n> of a mixture of complexes of analyte M with reagent L in the respective groups (distinguished by bars above the symbols) of the separation system. Calibration curve is derived from measurement of gross activity of complexes, A=A(ML_<n>) and . Theoretical relative error is expressed as a product of three terms, x/x=f₁f₂f₃. The first term f₁ depends on the degree of isotopic dilution, and the recommended ratio of amounts of nonradioactive (x) and radioactive (y) substance M is x/y(1;4). The second term f₂ depends first of all on the slope of distribution ratio (yield of separation ) vs. the analyte; reagent ratio, n(Z+1)/T. The form of slope is analyzed on the basis of the generalized separation reaction. Optimal conditions were discussed from this point of view and the ideal case is at f₂=1. The third term f₃ depends on the activities A and , i.e. on the distribution ratio, sample volumes, and the manner of counting. The ideal ratio of sample activities is A= and the optimal interval (0.2;0.8) is suggested     

Oscillatory variation in yields of I2 and the reactivity of γ-irradiated TiO2 in KI solution

The reactivity of preheated and -irradiated TiO₂ was observed in KI solution by studying the kinetics of liberation of I₂. The rate of the reaction was found to be low. species proposed on the surface of oxide probably dissociate into . surface sites which oxidize I^– ions to produce free I₂. During irradiation and are produced which are reducing in nature and therefore very low yields of I₂ are observed for low -doses. In further irradiation the reformation of –O–O–, peroxy linkages is proposed hence the observed higher yields. All the processes ultimately lead to an oscillatory variation in yields of I₂ with -doses.