Mixed pseudohalide complexes of copper(II). Crystal and molecular structure of [Cu(N3)(NCS)(tmen)] n and of [Cu(N3)(NCO)(tmen)]2 (tmen = N,N,N′,N′-tetramethylethylenediamine)

The compounds [Cu(N₃)(NSC)(tmen)]_n (1), [Cu(N₃)(NCO)(tmen)]_n (2) and [Cu(N₃)(NCO)(tmen)]₂ (3) (tmen=N,N,N′,N′-tetramethylethylenediamine) were synthesized and studied by i.r. spectroscopy. Single crystals of compounds (1) and (3) were obtained and characterized by X-ray diffraction. The structure of compound (1) consists of neutral chains of copper(II) ions bridged by a single azido ligand showing the asymmetric end-to-end coordination fashion. Each copper ion is also surrounded by the other three nitrogen atoms; two from one N,N,N′,N′-tetramethylethylenediamine and one from a terminal bonded thiocyanate group. Compound (2) decomposes slowly in acetone and the product formed [Cu(N₃)(NCO)(tmen)]₂ (3) crystallizes in the monoclinic system (P2₁). The structure of (3) consists of dimeric units in which the Cu atoms are penta-coordinated and connected by μ(1,3) bridging azido and cyanate ligands. In both cases the five coordinated atoms give rise to a slightly distorted square-based pyramid coordination geometry at each copper ion. The thermal behavior of [Cu(N₃)(NSC)(tmen)]_n (1) and [Cu(N₃)(NCO)(tmen)]_n (2) were investigated and the final decomposition products were identified by X-ray powder diagrams.     

Synthesis,spectral and thermal studies on pyrazolatebridged palladium(II) coordination polymers

Synthesis, spectroscopic characterization and thermal behavior of pyrazolate-bridged palladium complexes [Pd(μ-Pz)₂]_n (1), [Pd(μ-mPz)₂]_n (2), [Pd(μ-dmPz)₂]_n (3), [Pd(μ-IPz)₂]_n (4) {pyrazolate (Pz^–), 4-methylpyrazolate (mPz^–), 3,5-dimethylpyrazolate (dmPz^–), 4-iodopyrazolate (IPz^–)} have been described in this work. The exobidentate coordination mode of pyrazolato ligands in 1–4 was inferred on basis of IR spectroscopic evidences. TG investigations indicated that the introduction of substituents at the 4 position in the pyrazolyl moiety into coordination polymers do not affect significantly their thermal stability, whereas at the 3 and 5 position reduced the stability of the main chain. Metal palladium was the final product of the thermal decompositions, which was identified by X-ray powder diffraction.     

Thermal and Spectroscopy Investigation of Cyclopalladated Compounds of the Type [Pd(C13H10N)(μ-X)]2, (X=H3CCOO,NCO, SCN,CN)

The dimeric compound [Pd(bzan)(μ-OOCCH₃)]₂ (1) (bzan=N-benzylideneaniline) reacts with KX, in methanol/acetone (2:1), affording the analogous dimeric pseudohalogen-bridged species [Pd(bzan)(μ-X)]₂ [X=NCO(2),SCN(3), CN(4)]. The compounds were characterized by elemental analysis, infrared spectroscopy, NMR and thermogravimetric analysis. IR data for 2–4 showed bands typical of coordinated pseudohalogen ligands clearly indicating the occurrence of the exchange reaction. Their thermal behaviour was investigated and suggested that their stability is influenced by the bridging ligand. The thermal stability decreased in the order[Pd(bzan)(μ-CN)]₂>[Pd(bzan)(μ-SCN)]₂>[Pd(bzan)(μ-OOCCH₃)]₂>[Pd(bzan)(μ-NCO)]₂. X-ray results showed the formation of Pd° as final decomposition product. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal BEHAVIOR of the Ti(IV), Zr(IV) and Pb(II) Complexes with 5-nitro-8-hydroxyquinoline

Ti(IV), Zr(IV) and Pb(II) complexes with 5-nitro-8-hydroxyquinoline (5-NQ) were obtained by precipitation in acetone/ammonium solution medium. The compounds TiO(C₉H₅N₂O₃)2·;0.5H₂O, ZrO(C₉H₅N₂O₃)₂·₂H₂O and Pb(C₉H₅N₂O₃)₂ were characterized by Elemental Analysis, X-ray Diffratometry and Infrared Absorption Spectrometry and their thermal behavior followed by TG/DTA. This present study intends to show the variations in the thermal behavior of the compounds and in the composition and/or structure of final oxide residues, in different atmospheres and heating rates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal and Crystalographic Studies of Mixture La2O3-SrO Prepared Via Reaction in the Solid State

The compound obtained via state solid reaction of the La₂O₃ and SrO oxides and expose the room atmosphere shows the crystallographic data of the compound reported as La₂SrO_x. However, thermogravimetric, differential thermal analysis and XRD with controlled temperature indicated that the stoichiometry of the compound is 2La(OH)₃-SrCO₃, which structural parameters were determined by using the Rietveld method. It was verified that when the compound exposed at room atmosphere, the mixture oxide absorbs H₂O and CO₂ producing hydroxide and carbonate of lanthanum and strontium, respectively, which thermal decomposition occurs by the same steps, producing the La₂O₃-SrO. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Behaviour of Tin(II) Complex With 8-hydroxyquinolinate in the Solid State

Tin(II) complexes with 8-hydroxyquinolinate in solid state have been obtained by adding aqueous ammonium to a solution containing stannous chloride and 8-hydroxiquinoline in medium of HCl and acetone up to pH 5 and 9, respectively. The products obtained show the same composition, Sn(C₉H₆ON)₂; however there are some differences regarding both the thermal behaviour in an oxidant atmosphere and morphology. These products were characterised by elemental and complexometric analysis, TG and DTA curves, infrared and X-ray diffractometry. TG curves show, above 448 K, the partial oxidation on air atmosphere of Sn(II) complexes to Sn(IV) complexes, SnO(C₉H₆ON)₂. This behaviour does not depend only on pH in which the compounds were obtained but also on the heating rate in TG curves. Sn(II) complexes volatilise almost completely on nitrogen atmosphere and partially on air atmosphere depending on the oxidation degree of the compound. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sublimation/Volatilisation Kinetics of 8-hydroxyquinolines and Their Nitro-derivatives

5-Nitro-8-hydroxyquinoline (B) and 5,7-dinitro-8-hydroxyquinoline (C) were obtained from nitration of 8-hydroxyquinoline (A) and purified in acetone medium and under heating in which the formation of (B) or (C) depends on the amount of HNO₃ added. TG curves present mass loss in only one step before and after the melting point (T _m =76°C (A) and 180°C (B)) in different proportions as a function of the heating rate, characterising the sublimation and the volatilisation processes, respectively. The thermal stability of the compounds follow the order: A (77°C)<B (121°C)<C (222°C). Kinetic parameters through TG curves, dynamic process, using heating rates of 1, 2.5, 5, 10 and 20°C min^ȡ1 , enabled to obtain the following increasing order to the activation energy values of the compounds: 80.4 (A), 102.0 (B) and 153.9 kJ mol⁻¹ (C). Other kinetic parameters as pre-exponential and half-lifetime were also estimated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Attainment of lead titanate

Crystalline PbTiO₃ was obtained through the thermal decomposition of 8-hydroxyquinolinate of lead(II) and that of titanium(IV), which was monitored by TG/DTG/DTA under different atmospheric conditions and with varying heating rates. The compound was prepared from adding 8-hydroxyquinoline solution in the solution of metallic ions Pb(II):Ti(IV) (1:1) under constant stirring at 3°C, having the pH adjusted to 10. The results of these investigations show that different thermal behavior related to the precursor occurred and also the consequent formation of residues which have different crystallinities. No carbonate residues from the thermal decomposition could be determined by XRD and IR. Only PbTiO₃ was observed and confirmed by DSC at 470°C, temperature lower than the tetragonal-cubic transition. This revised version was published online in August 2006 with corrections to the Cover Date.