Heat capacity study of double perovskite-like compounds BaTi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>x</Subscript>O<Subscript>3</Subscript>

The temperature dependence of the heat capacity of two compositions in the solid solution system BaTi_1?xZr_xO₃ (x = 0.25, 0.35) was measured using adiabatic calorimetry. In the T-x phase diagram, these compounds occupy positions near the crossover from conventional ferroelectric behavior to the relaxor state. Both compounds reveal diffuse heat capacity anomalies: two anomalies in the temperature ranges 250–350 and 150–200 K at x = 0.35 and one anomaly within the range ～150–320 K at x = 0.25. The results obtained are discussed together with structural and dielectric measurements.     

Crystal structure and thermal behavior of two new organic monosulfates NH3(CH2)5NH3SO4 1.5H2O and NH3(CH2)9NH3SO4 H2O

The chemical preparation, the calorimetric studies and the crystal structure are given for two new organic sulfates NH₃(CH₂)₅NH₃SO₄ 1.5H₂O (DAP-S) and NH₃(CH₂)₉NH₃SO₄·H₂O (DAN-S). DAP-S is monoclinic P2₁/n with unit cell dimensions: a=11.9330(2) Å; b=10.9290(2) Å; c=17.5260(2) Å; β=101.873(1)°; V=2236.77(6) Å³; and Z=8. Its atomic arrangement is described as inorganic layers of units and water molecules separated by organic chains. DAN-S is monoclinic P2₁/c with unit cell parameters: a=5.768(2) Å; b=25.890(10) Å; c=11.177(5) Å; β=115.70(4)°; V=1504.0(11) Å³ and Z=4. Its structure exhibits infinite chains, parallel to the [100] direction where the organic cations are interconnected. In both structures a network of strong and weak hydrogen bonds connects the different components in the building of the crystal.     

Volatile constituents of two Hypericum species from Tunisia

The chemical composition of the essential oils obtained by hydrodistillation from the aerial parts of the Tunisian Hypericum perforatum and H. ericoides ssp. roberti was elucidated by a combination of GC and GC-MS analyses. The main constituents of the oil of H. perforatum were alpha-pinene (11.8%), alpha-ylangene (10.4%), germacrene-D (9.5%), n-octane (6.5%) and alpha-selinene (5.9%). The oil of H. ericoides ssp. roberti exhibited a higher amount of aliphatic and branched hydrocarbons and the main constituents were n-octane (29.1%), alpha-pinene (10.9%), pulegone (7.7%) and acetophenone (7%). Both qualitative and quantitative differences were observed between the studied oils. This chemical variability seems likely to result from the genetic variability, since samples of both species were collected at the same location and processed under the same conditions.     

Global Stabilization of a Class of Bilinear Systems in $${\mathbb{R}^3}$$

In this paper, we consider a class of bilinear systems in dimension three which can be an extension of another one in \({\mathbbm{R}^{2}}\). We prove that there exists some homogeneous feedback of degree zero stabilizing the considered class if and only if these feedbacks are constants.     

One‐Pot Synthesis of 3,5‐Disubstituted Pyridin‐2‐ones by Annulation of β‐Keto‐amides with 2‐Dimethylaminomethylene‐1,3‐bis(dimethylimonio)propane Diperchlorate

β‐Keto‐amides react with 2‐dimethylaminomethylene‐1,3‐bis(dimethylimonio)propane diperchlorate salt to give the corresponding 3‐acetyl‐5‐formylpyridin‐2‐ones. The annulation reactions proceed with excellent yields.     

Solid-state single and triple-quantum 93Nb MAS NMR studies of ferroelectric Pb(Mg1/3Nb2/3)O3 and a related pyrochlore

Pb(Mg1/3Nb2/3)O3 (PMN), a well-known relaxor ferroelectric material, and a related pyrochlore phase have been studied by single- and triple-quantum 93Nb MAS NMR spectroscopy. The assignment of the NMR resonances has been attempted.     

Une extension de la méthode CNDO/2 á l'étude des complexes d'éléments de transition

An extension of the CNDO/2 formalism, similar to the method of Clack, Hush and Yandle but with a different parametrisation, is proposed for investigating the electronic structure of transition metal complexes. The results for Ni(CO)₄ and Ni(PF₃)₄ agree well with those ofab initio calculations and with some experimental data. Such a semi-empirical approach may be performed, usingab initio results as reference data, in order to interpret the physical and chemical behaviour of largeseries of complexes in their ground state.