G. Punte

Kinetic study of the disproportionation of tin monoxide

Abstract The disproportionation reaction kinetics of tin monoxide at 723 K was studied by Mossbauer spectroscopy. The kinetic parameters of the reaction were obtained by objective data processing of the Mossbauer spectra, treating the data matrix with the Single Value Decomposition procedure that, in addition, yields the spectrum of the intermediate oxide. The procedure was applied on the assumptions that the f-factors of Sn(II) and Sn(IV) atoms belonging to the intermediate oxide are equal to those of Sn(II) and Sn(IV) atoms of SnO and SnO2, respectively, that the stoichiometry of the intermediate oxide is Sn3O4, and that the disproportionation proceeds by a set of two successive first order reactions described by the sequence SnO→intermediate oxide→SnO2. The kinetic rate constants obtained for the first and second reactions were k1=2.47×10−4 s−1 and k2=1.13×10−5 s−1, respectively. The time-profile of the mole fraction of each component in partially reacted samples shows that at 723 K, the intermediate accumulates in the time bracket between ca. 100–1000 min.

Crystal data and vibrational spectra of the rare earth decavanadates

Abstract Crystallographic data for the full series of rare earth decavanadates of the type Ln2V10O28·nH2O have been obtained from monocrystals by precession and Weissenberg measurements. The substances belongs to four different structural groups and their characteristics are briefly discussed. The vibrational spectra of the compounds have also been recorded and interpreted.

Phase transformations in Fe-doped cupric oxide

Abstract This work is a study of 57 Fe-doped CuO samples intended to obtain a compound of nominal composition (Cu 1− x Fe x )O ( x = 0.005; 0.010) through the nitrate route and solid state reactions. Afterwards, the samples were mechanically ground for different times. The specimens were characterized by Mossbauer Spectroscopy and X-ray diffraction. For samples that were not mechanically ground, the iron phases were tetragonal and cubic CuFe 2 O 4 spinel, and CuFeO 2 , delafossite, independent of the preparation method with no evidence of Fe inclusion into the CuO lattice. For mechanically ground samples, a metastable paramagnetic phase has been found.

History-dependent magnetic properties in pure and Zn-doped cupric oxide

Abstract Magnetization curves taken in zero-field-cooling and field-cooling regimes on pure CuO and Zn-doped CuO samples demonstrate thermal irreversibility. For the Zn-doped sample, this is present above the Neel temperature ( T N ) and is reinforced below T N . Hysteresis is related to inherent frustration of the magnetic structure of CuO.

Experimental evidence for the amino-group non-planarity in nitroanilines: neutron diffraction study of 2-methyl-5-nitroaniline at 100 K

An appreciable degree of pyramidalization of the amine N atom is observed in the title compound. The existence of polar chains, induced by N-H.O synthons, is confirmed. C-H.O interactions, not noted in a previous X-ray study, were found to stabilize further the known head-to-tail assembling of the chains. The structure can be described as non-polar (101) layers, embodying chains interlinked by centrosymmetric dimers, connected by C(aryl)-H.pi interactions. The latter are not present in m-nitroaniline, 2-methyl-4-nitroaniline and other related compounds with chains built from similar N-H.O synthons and assembled head-to-head. This finding implies that an obvious relationship between molecular recognition patterns and crystal structures should not be assumed.

COORDINATION BINDING MODES FOR POLYMERIC CADMIUM DICARBOXYLATE HYDRATE COMPLEXES

Abstract Single crystal X-ray crystal diffraction, IR and TGA-DTA data and searches in the Cambridge Structural Database (CSD) have been used to analyze coordination binding modes of Cd(II) in dicarboxylate complexes with anions of different length. The results, discussed in this paper, show that Cd(II) presents a range of coordination geometries. Six, seven and eight coordination with different degrees of departure from regular polyhedra are observed. The length of the ions influences the availability of donor oxygens and induces bidentate, six or four member chelating rings, and monodentate binding, which produces polymerization of different dimensionality.

X-ray structural and spectroscopic investigation of 1-piperidine-2,4-dinitrobenzene

The crystal structure of the title compound (C11H13N3O4) has been determined by single-crystal X-ray diffraction. The compound is monoclinic, space group P21/n, witha=9.968(2),b=9.156(2),c=13.249(2)Å, β=102.05(2)°, andDx=1.563 gcm−3 forZ=4. The aromatic ring shows a slight boat deformation. Theo- andp-NO2 groups are twisted out of the plane of the phenyl ring by 39.0(2)° and 4.4(1)°, respectively. The piperidine ring exhibits a slightly deformed chair conformation. Short C−H...O intermolecular contacts stabilize the three dimensional structure. UV and NMR data indicate that the molecule in solution presents a conformation similar to that of the the solid state.

Conformational studies of trans-1,4-substituted cyclohexanes. I: Trans-1,4-cyclohexanedicarbonitrile

The molecules of the title compound (C 8 H 10 N 2 ), which each adopt a chair conformation with the CN substituents equatorially bonded, lie on crystallograpbic inversion centres and are linked by CN...CN intermolecular interactions to form (101) sheets. The sheets are additionally stabilized by short C-H...N contacts

Diytterbium decavanadate 24-hydrate, Yb2V10O28.24H2O

Mr= 1735.85, triclinic, P1, a = 9.287 (5), b=9.821(5), c=23.33(2)A, a=99.13(15), fl= 81.51(15), y=90.57(4) ° , V=2077(3)A 3, Z=2, D m = 2.7, D x = 2.77 Mg m -3, ,;l,(Mo K~t) = 0.7107/~, /t=6.3mm -~, F(000)=1668, T=298+2K, R= 4.4% for 4559 independent observed reflections. The unit cell contains two independent (V10028) 6- anions located on symmetry centers and four (Yb(H20)8) 3+ polyhedra. The V-O distances within the polyanions range between 1.578 (4) and 2.346 (5)/~,. The coor- dination geometry at Yb 3+ ions is a distorted square antiprism with Yb-water-O distances ranging between 2.255 (6) and 2.428 (7)/k. The 16 interstitial water molecules are inserted between layers parallel to (001) containing decavanadate groups and rare-earth poly- hedra which are not in direct contact. A net of hydrogen bonds stabilizes the structure. Introduction. Crystallographic studies on hydrated rare-earth decavanadates were undertaken as part of a more general research program on crystal chemistry and physicochemical properties of decavanadate salts (Rigotti, Punte, Rivero, Escobar & Baran, 1981). The structures of the 25-hydrate rare-earth salts (Rivero, Rigotti, Punte & Navaza, 1982, 1984) and that of the 24-hydrate compound presented here were solved in order to correlate structural changes with ionic-radius size and with the different number of water molecules of crystallization.

On the Electron Density Topology and Electrostatic Properties of Nitroanilines. A Theoretical Investigation on m-Nitroaniline and 2-Methyl-5-nitroaniline Crystals

On the basis of the AIM theory, intermolecular interactions have been characterized in the B3LYP/6-31G** periodic electron density of the title compounds. Although the set of bond paths identified in each system is not fully equivalent to its experimental counterpart, agreement is reasonable with regard to the nature and relative importance of the intermolecular interactions at play. Within the AIM partition scheme, the molecular dipole moment of the in-crystal molecule was determined for the title compounds and the two closely related crystals of 2-methyl-4-nitroaniline and p-nitroaniline. Using a method that relies only on molecular calculations and a mean electric field approximation, it was possible to reproduce within 6% the values of the molecular dipole moment modulus obtained directly from the periodic electron densities. This result reveals that, for this kind of molecular crystal, enhancement of the dipole moment in going from the isolated molecule to the in-crystal one is an almost exclusively inductive effect.