X-ray diffraction and solid-state NMR studies of a germanium binuclear complex

A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2] x 4 H2O (where pmida(4-) = N-(phosphonomethyl)iminodiacetate and C4H12N2(2+) = piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2- complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H-X(13C,31P) heteronuclear correlation (HETCOR) and 1H-1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee-Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic-organic hybrids. We assigned the NMR resonances with the help of C...H and P...H internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X-ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry).     

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.     

Application of modified Neumann expansion for analytical evaluation of two-center,two-electron integrals over slater-type orbitals

A modified form of the Neumann expansion in terms of products of orthogonal polynomials for the inverse interelectronic distance r¹₁₂ is proposed. This expansion has been applied in order to derive a unified analytical formula for two-center and two-electron integrals over Slater-type orbitals. The results are equivalent to those given recently by Yasui and Saika, but the expansion itself can be used for building up a realistic algorithm for evaluation of three- and four-electron integrals determined by using correlated variational wave functions.     

Magneto-optics of Ferritin

Measurements of Rayleigh light scattering, nonlinear light scattering in DC magnetic fields, and the Cotton-Mouton effect were carried out for 15 mM NaCl and water solutions of ferritin at room temperature. The spherical geometry of the molecule implies that it is optically isotropic. Such a macromolecule should not manifest magnetic anisotropy; however, in solution it shows induced magnetic birefringence (Cotton-Mouton effect) and changes in the intensity of the scattered light components. The analysis of the obtained results indicates the deformation of linear optical polarizability induced in the ferritin by a magnetic field as the main source of the magneto-optical phenomena observed. Light scattering and the CM effects theoretically depend on the linear magneto-optical polarizability, chi, and the nonlinear magneto-optical polarizability, eta. Using the theory describing the phenomena as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizability components, chi(parallel) - chi(perpendicular) = -(1.3 +/- 0.7) x 10(-22) [cm3] (in SI units chi(parallel) - chi(perpendicular) = -(2.0 +/- 1.2) x 10(-33) [m3]), the linear optical polarizability, alpha = (alpha(parallel) + 2alpha(perpendicular))/3 = (3.9 +/- 1.0) x 10(-20) [cm3] (in SI units alpha = (3.52 +/- 0.09)x10(-4) [Cm2 V(-1)]), and its anisotropy, kappa(alpha) = (alpha(parallel) - alpha(perpendicular))/3alpha = -(0.06+/-0.03), nonlinear magneto-optical polarizability, eta = (eta(parallel) + 2eta(perpendicular))/3 = -(4.7 +/- 0.9) x 10(-30) [cm3 Oe(-2)] (in SI units eta = -(6.7 +/- 1.3) x 10(-18) [Cm4 V(-1) A(-2)]) and its anisotropy, kappa(eta) = (eta[parallel) - eta(perpendicular))/3eta = -(0.15 +/- 0.10), were deduced. Here alpha(parallel), eta(parallel), alpha(perpendicular), eta(perpendicular) are the optical and magneto-optical polarizability components along the parallel and the perpendicular axes of the axially symmetric molecule, respectively.     

Thermal Analysis of Hexachloroplumbate and Chlorides Containing Complex Divalent Lead 2,2'-bipyridine Cations

Lead(II) 2,2'-bipyridine hexachloroplumba tetetrahydrate was synthesized and investigated by DTA, TG and DTG. IR spectroscopy and other methods enabled the identification of some of the decomposition products. Comparative studies on the corresponding chlorides: [Pb(bipy)]Cl₂ and [Pb(bipy)₃]Cl₂, which can be considered as precursors of the hexachloroplumbate, were also undertaken. X-ray measurements enabled the tentative determination of the crystal structure of [Pb(bipy)]Cl₂. Hexachloroplumbate decomposes with the liberation of chlorine, water and organic ligands, and the process is accompanied by the simultaneous transition of Pb(IV)→Pb(II). Chlorides release only ligands upon heating. Residues comprised always PbCl₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

New insights into the reaction of zinc alkyls with dioxygen

Studies on the reaction of zinc alkyls with O2 are reported which demonstrate that the selective oxygenation of organozinc compound is viable. The reaction of [EtZn(azol)]n (azol = deprotonated 1-aziridineethanol) with an excess of dry O2 in toluene affords the zinc ethylperoxide [EtOOZn(azol)]2[EtZn(azol)]2, while the analogous reaction between Me2Zn and O2 results in the isolation of the Me6Zn7(OMe)8 cluster in high yield.     

Determination of sulphur by electrolytic hydrogenation

Certain sulphur compounds such as thiosulphuric acid, polythionic acids, thiocyanic acid, thioureas, thioamides and 2-mercapto-acids are readily electrolytically hydrogenated in 1N sulphuric acid to form hydrogen sulphide which is absorbed in potassium hydroxide solution and titrated with o-hydroxymercuribenzoic acid in the presence of dithizone as indicator. The electrolytic cell consists of a lead anode in 5N sulphuric acid, a porous ceramic tube as diaphragm, and a cathode made of soft iron. The first-order rate-constants of hydrogenation and the results of determination of sulphur in some sulphur compounds are presented. The limit of determination is 0.1 ppm.     

Primary and secondary relaxations in bis-5-hydroxypentylphthalate revisited

The molecular structure of bis-5-hydroxypentylphthalate (BHPP) is like dihexyl phthalate but having appended to it two hydroxyl end groups, which contribute additional dipole moments and capacity for hydrogen-bond formation. In a previously published dielectric study of the primary and secondary relaxations of BHPP, it was found that all the dynamic properties are normal except for the anomalously large width of the primary relaxation loss peak. There are two secondary relaxations, the relaxation time of the slower one increases with increasing pressure, whereas that of the faster one is practically insensitive to pressure. Hence, the slower secondary relaxation is the "universal" Johari-Goldstein (JG) [J. Chem. Phys. 53, 2372 (1970); 55, 4245 (1971)] relaxation in BHPP. All is well except if the observed large width of the primary relaxation were an indication of a corresponding large coupling parameter n=0.45 in the coupling model. Then the predicted relations between the primary relaxation time tau(alpha) and the JG relaxation time tau(JG) found previously to hold in many glass formers would be violated. It was recognized that this singular behavior of BHPP is likely due to broadening of the primary loss peak by the overlapping contributions of two independent dipole moments present in BHPP, and the actual coupling parameter is smaller. However, at the time of publication of the previous work there were not enough data to support this explanation. By making broadband dielectric measurements of dibutyl phthalate (DBP) and dioctyl phthalate (DOP) that have chemical structures closely related to BHPP but with only one dipole moment, we show that all their dynamic properties are almost the same as BHPP but the widths of their primary relaxation loss peaks are significantly narrower corresponding to a smaller coupling parameter n=0.34. The new data presented here indicate that the coupling parameter of BHPP is about the same as DBP and DOP, and the predicted relations between tau(alpha) and tau(JG) of BHPP are brought back in agreement with the experimental data.     

Apparent molar volumes,heat capacities,and molecular excluded volumes of methylated,hydroxy and methoxy derivatives of 1-methylcytosine in aqueous solutions at 25°C

Densities and specific heat capacities of aqueous solutions: 1-methylcytosine; 1-methyl-N⁴-hydroxycytosine; 1,5-dimethylcytosine; I,N⁴-dimethylcytosine; 1,5-dimethyl-N⁴-hydroxycytosine; 1-methyl-N⁴-methoxycytosine; 1,N⁴,N⁴-trimethylcytosine, 1,5-dimethyl-N⁴-methoxycytosine were determined using flow calorimetry and flow densimetry at 25°C. Apparent molar volumes and heat capacities were then determined. Molecular excluded volumes were evaluated. A relationship was found between the values of the increments in partial molar values and the kind of groups substituted. Four types of contributions were distinguished: substitution of hydrogen on C, N, and O (in OH group on N4) atoms by CH₃ group and replacement of hydrogen on N4 atom by OH group. The correlation between the experimental partial molar volumes and calculated molecular excluded volumes was also elaborated.     

Optimized conditions for hydrocarbon group type analysis of base oils by thin-layer chromatography-flame ionisation detection

The results of research on the optimization of the thin-layer chromatography-flame ionisation detection for the determination of group composition of natural base oils, including separation of the aromatics into subgroups, are presented. Neutral base oils obtained in several steps of refining from vacuum distillation petroleum fractions are the most difficult to analyze by hydrocarbon group type analysis (HGTA) because of the high content of aliphatic fragments in their molecules. Factors affecting the accuracy and precision of the results were identified. The paper presents the analytical procedure, including two different calibration methods, as well as the results of studies on the reproducibility of HGTA of typical base oils of different viscosity classes under the optimized conditions. The same conditions were found suitable for HGTA of other high-boiling petroleum fractions by TLC with flame ionisation detection. The paper also introduces a new procedure for reproducible determination of polar fractions in base oils utilizing solid-phase extraction columns, and presents a corrected procedure for the determination of saturated compounds and aromatics (mono-, bi- and polycyclic) in base oils by column liquid chromatography.