Graciela Rigotti

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.

The crystal chemistry of copper(II) dipicolinates

Abstract The molecular structure of a new copper dipicolinate, Cu(dipic)(H2dipic)·H2O, and a refinement of the previously reported Cu(dipic)(H2dipic)·3H2O are presented. The Jahn-Teller effect, as operative in six-coordinated CuII surrounded by two planar tridentate ligands, is responsible for the presence of a dianion and a neutral acid molecule in the structure. As opposed to previously reported copper dipicolinates, water molecules do not coordinate and in the trihydrate dehydration is facile because interstital water finds easy dehydration pathways; the mechanism involves nucleation and fast bidimensional growth. The monohydrate, however, presents tightly bound (through hydrogen bonds) water and no easy dehydration pathways are available; the dehydration mechanism involves fluid-flux nucleation, mediated by fusion. Five different copper(II) dipicolinates are known; because of the strong tendency of this ligand to form tridentate mononuclear complexes, all of them, except monoclinic Cu(dipic)·2H2O, belong to the class of molecular solids. In the monoclinic dihydrate, carbonyl O atoms are involved in defining chains that run parallel to [001] planes.

The crystal and molecular structure of sodium hexacyanoosmate(II) decahydrate and related hexacyanometalate complexes

The crystal structures of sodium hexacyanoosmate, ruthenate and ferrate decahydrates, Na4M(CN)6·10H2O(M=Os, Ru, Fe), have been determined from X-ray diffraction data and refined by full matrix least-squares to final agreement values: R = 0.038, Rw = 0.039; R = 0.026, Rw = 0.041; R = 0.060, Rw = 0.043 for Os, Ru and Fe compounds, respectively. The compounds are isostructural and crystallize in the monoclinic space group P21/n, Z = 2, with a = 9.154, b = 11.506, c = 9.876 A, β = 97.95°; a = 9.146, b = 11.486, c = 9.867 A, β = 98.00°; a = 9.038, b = 11.450, c = 9.782 A, β = 97.57°, for Os, Ru and Fe compounds, respectively. The structure can be described as layers of hexacyanometallate anions, intercalated with layers of sodium polyhedra containing hydration water molecules and N atoms, perpendicular to the crystallographic ac plane. MetalC and CN distances for the hexacyanide anions are correlated with those from other structurally related moieties. The infrared spectra of the compounds are complementary with previous results for potassium salts.

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.

Structure and reactivity of copper (II) carboxylates I. Copper (II) dipicolinates

Abstract The crystal and molecular structures of a series of salts formed by copper (II) with dipicolinic acid were used to interpret the dehydration behavior. The morphology of single crystals dehydration of Cu(dipic)·2H 2 O (monoclinic and triclinic symmetry), Cu(dipic)·3H 2 O and Cu(dipic) (H 2 dipic)· x H 2 O was shown to be governed by the arrangement of water molecules along specific orientations.

Structure and reactivity of copper (II) carboxylates II. Copper (II) bis(hydrogen o-phthalate) dihydrate

Abstract The dehydration behavior of copper(ii) bis (hydrogen o-phthalate)dihydrate is interpreted in terms of its crystal structure. Single crystal XRD data were used to derive important structural parameters. The TD of the anhydrous salt is also discussed in terms of proton transfer between adjacent anions.

Surface nucleation and anisotropic growth model for solid state reactions

Abstract Mathematical equations are derived that relate the extent of reaction α to time for the case of a reaction starting through surface nucleation and proceeding inwards and laterally through two growth-rate constants. The model is based in Avramis theorem, and may therefore be considered as a modified Avrami model. The relation between −In(1−α) and time involves first-order Bessel functions Y 1 [2 ωμ ( t )] and J 1 [2 ωμ ( t )], where μ(t)=exp(−k n t 2 ) and ω 2,= σδ 0 k 1 k n −1 , ω is one of the model basic parameters. The final equations may be solved analytically under certain conditions, and numerically in the more general cases.

Surface nucleation and anisotropic growth model for the dehydration of 11-aminoundecanoic acid dihydrate

The experimental results of the title reaction were modeled as a nucleation and growth process. Nucleation is restricted to the lateral faces of the platelets of the parent hydrate (space group Cc), and growth is anisotropic, two rate constants (for lateral and normal growth) being introduced. The results are compared with the empirical description given by Avramis equation, and shown to rationalize the data adequately. In particular, the influence of water vapor pressure is discussed.

Crystal data for magnesium decavanadate. Mg3V10O2828.H2O

Crystal data for Mg3V10O28.28H2O were determined from oscillation, Weissenberg and precession photographs using Cu Kα radiation (λ = 1.54178 A). The substance is triclinic, space group P{\bar 1}, Z = 2, and lattice constants a = 10.53 (5), b = 10.73 (6), c = 21.28 (9) A, α = 90.2(1), β = 97.5(2) and γ = 104.1(3)°, V = 2310 (25) A3 and the measured and calculated densities are 2.17(10) and 2.20 Mg m−3, respectively. The crystals were also characterized by TG/DTA measurements and vibrational spectroscopy.