Influence of preparation conditions on thermal properties of lanthanide benzenepolycarboxylates

Properties of lanthanide 1,2,4-benzenetricarboxylates and lanthanide 1,2,4,5-benzenetetracarboxylates obtained by a classical synthesis method and under hydrothermal conditions were compared. Solid 1,2,4-benzenetricarboxylates and 1,2,4,5-benzenetetracarboxylates of cerium, neodymium and erbium were prepared by a classical precipitation method. The same lanthanide compounds were obtained also from hydrothermal reaction. All obtained products were examined by elemental analysis. General formulae of complexes were: Ln(1,2,4-btc)·xH₂O and Ln₄(1,2,4,5-btec)₃·yH₂O. The thermal analysis shows that hydrothermal conditions cause the coordination of less number of water molecules to complex molecule. Because lanthanide ions exhibit the most often the coordination number equal 8 or 9 one can conclude that the coordination ability of carboxylic groups under hydrothermal conditions is different from that under mild ones. Probably, in hydrothermal conditions the carboxylic groups of 1,2,4-benzenetricarboxylate ions are able to form more coordination bonds with lanthanide ions than under normal pressure.     

Multipeak distributions of first passage times in bistable dynamics in a model of a thermochemical system.

A master equation is used to study transitions between the stable limit cycle and stable focus in the two-variable bistable system. The distribution function of the mean first passage time between these attractors and the relative dispersion of the mean first return time from the stable focus to itself as a function of the intensity of fluctuations are calculated and discussed. A coherence resonance is observed for the return time from the focus to itself.     

Free-electron attachment to coronene and corannulene in the gas phase

Electron attachment to the polyaromatic hydrocarbons coronene and corannulene is studied in the electron energy range of about 0-14 eV using a high-resolution crossed electron-neutral beam setup. The major anions observed are the parent anions peaking at about 0 eV with cross sections of 3.8 x 10(-20) and 1 x 10(-19) m(2), respectively. The only fragment anions formed in coronene and corannulene are the dehydrogenated coronene and corannulene anions. Other anions observed in the negative mass spectra at about 0 eV can be ascribed to impurities of the sample. High-level quantum-mechanical studies are carried out for the determination of electron affinities, hydrogen binding energies, and structures of both molecules. The behavior of coronene and corannulene upon electron attachment is compared with that of other polyaromatic hydrocarbons studied previously.     

X‐ray investigations of bicyclic α‐methylene‐δ‐valerolactones. V. (4aS,7R,8aR)‐7‐Isopropenyl‐4a‐methyl‐3‐methyleneperhydrochromen‐2‐one

The title compound, C₁₄H₂₀O₂, adopts a conformation in which the δ‐valerolactone and cyclohexane rings are almost coplanar with one another. The γ‐methyl substituent occupies an axial position with respect to the cyclohexane ring. The δ‐valerolactone moiety adopts an envelope arrangement, while the cyclohexane ring exists in a chair conformation.     

Calorimetric studies of refractory corundum

Calorimetry has been used in the investigations of calcium aluminate materials produced as a binder for aluminate-corundum composites of high refractoriness. The kinetics and of hydration process was thus characterized and the optimum compositions of initial binders and cement-corundum refractory filler blends could be selected for further tests. The acceleration of heat evolution - the shortening of so-called induction period and relatively high heat output in the presence of corundum was observed. It means the acceleration of hydration process, that is early crystallisation of hydration products and subsequent further dissolution of initial anhydrous aluminate phases. In the presence of fine grained corundum particles these phenomena should be attributed to the nucleating effect of fine corundum particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural Study of C-undecylcalix[4]resorcinarene Solvate with Dioxane

The crystal structure of the molecular complex of C-undecylcalix[4]resorcinarene with dioxane has been determined by X-ray analysis. The asymmetric unit contains one host and four guest molecules. The calix[4]resorcinarene moiety adopts a bowl conformation with C_4v symmetry. Four undecyl chains are axially oriented. Calix molecules are packed in a bowl-to-bowl fashion with alternating hydrophilic and hydrophobic layers. One of the hydrophilic dioxane molecules is located at the rim of the calix moiety and is hydrogen bonded to the other one. There is no interaction to attract, or direct the dioxane molecule into the interior of the cavity. There is an exo complex formed. The dioxane molecules – located in the hydrophobic part – are highly disordered.     

Influence of Some Aggressive Media on Corrosion Resistance of Mortars With Spent Cracking Catalyst

The influence of spent catalyst from catalytic cracking in fluidized bed on the hydration process of cement and the properties of cement mortars were studied. The spent catalyst was used as an additive to cement in the mortars (10 and 20% of cement). The samples of mortars kept in water for28 days, then they were placed in sulfate and chloride media for 2 months (the control samples were kept in water for 3 months). After this time they were subjected to bending strength and compressive strength determinations. Thermogravimetric and infrared absorption studies were performed and capillary elevation, capability of binding heavy metals, and changes in mass and apparent density were determined too. The studies disclosed the pozzolana nature of spent catalyst and its influence on cement mortars being in contact with corrosive media. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reactions of nickel(II) 2,21-dimethyl-2-aza-21-carbaporphyrin with phenyl Grignard reagents, phenyllithium, and n-butyllithium

Addition of a phenyl Grignard reagent to a toluene solution of the nickel(II) chloride complex of a dimethylated inverted porphyrin, (2-NCH3-21-CH3CTPP)NiIICl (1), at 203 K results in the formation of a rare paramagnetic (sigma-phenyl)nickel(II) species, (2-NCH3-21-CH3CTPP)NiIIPh (2). The coordination of the sigma-phenyl in 2 is determined by a unique pattern of three sigma-phenyl resonances (ortho 375.0 ppm; meta 108.94 ppm; para 35.68 ppm (at 283 K)) in the 1H NMR and 2H NMR spectra. The (sigma-phenyl)nickel(II) compound 2 is in the high-spin ground electronic state (dxy)2(dxz)2(dyz)2(dz2)1(dx2-y2)1, as confirmed by similarity of the NMR spectra of the equatorial ligand in 1 and 2. Titration of 1 with phenyllithium produces (2-NCH3-21-CH3CTPP)NiIIPh (2). One-electron reduction with excess PhLi yields [(2-NCH3-21-CH3CTPP)NiIIPh]- (3), which can be also generated by independent routes, e.g., by reduction of (2-NCH3-21-CH3CTPP)NiIIPh using lithium triethylborohydride or tetrabutylammonium borohydride. The spectroscopic data indicate that (2-NCH3-21-CH3CTPP)NiIIPh (2) undergoes one-electron reduction without a substantial disruption of the molecular geometry. The presence of two paramagnetic centers in 3, i.e., the high-spin nickel(II) and the carbaporphyrin anion radical, produces remarkable variations in a spectral patterns, such as the upfield and downfield positions of pyrrole resonances (103.78, 96.66, -25.35, -50.97, -92.15, -114.83 ppm (at 253 K)) and sign alternations of the meso-phenyl resonances (ortho -77.81, -79.34 ppm; meta 48.77, 48.04 ppm; para -85.65, -86.46 ppm (at 253 K)). A single species, 4, is detected in the 1H NMR titration of 1 with n-butyllithium. The formation of one- or two-electron-reduced species, [(2-NCH3-21-CH3CTPP)NiBu]- or [(2-NCH3-21-CH3CTPP)NiBu]2-, respectively, is considered to account for the spectroscopic properties of 4 (pyrrole 17.33, 15.45, -5.79, -7.74, -14.62, -58.14 ppm; 21-CH3 3 ppm (at 203 K)). The temperature dependence of the hyperfine shifts of 4 demonstrates pronounced anti-Curie behavior, interpreted in terms of a temperature-dependent spin equilibrium between diamagnetic and paramagnetic states with diamagnetic properties approached as the temperature is lowered. Warming of 2-4 results in complete decomposition via homolytic/heterolytic cleavage of an axial nickel-apical carbon bond. In the case of 2 or 3, the process yields a mixture of two compounds, 5 and 6, which are detected by EPR spectroscopy, demonstrating the anisotropy of the g tensor (5, g1 = 2.237, g2 = 2.092, g3 = 2.090; 6, g1 = 2.115, g2 = 2.030, g3 = 1.940 (in frozen toluene solution at 77 K)).     

Cationic Heteroconjugation Constants in the OHN+ and NHO+ Systems in Propylene Carbonate: Dependence on Difference in Basicity

Cationic heteroconjugation equilibria of more than ninety systems consisting of substituted pyridines, their N-oxides, and trimethylamine N-oxide, i. e., in systems with mixed hydrogen bridges of type OHN⁺ (NHO⁺) were studied in propylene carbonate. Both experimental systems without proton transfer, BH⁺/B₁, and those with proton transfer, B₁H⁺/B, were explored. The stability of the mixed hydrogen bridges, OHN⁺ (NHO⁺), is compared with that of the OHC⁺-type bridges. The influence of the difference in basicity of the conjugate base of the proton donor and the proton acceptor on the presence of the proton transfer equilibria, and, consequently, the possibility of determination of the cationic heteroconjugation constant values is discussed.     

Artin algebras with only preprojective or preinjective modules are of finite type

This work was done while the second author visited Toru. This research was partially supported by the Polish Scientific Grant KBN No. 1222/2/91