Structural features of dibromobis(nicotinamide)zinc(II) complex

A novel ligand complex of Zn(II) with nicotinamide (one form of niacine) and two bromine ions were synthesised and characterised on the basis of elemental analysis, FT-IR spectroscopy and X-ray crystallography. Crystal system is monoclinic, space group C2/c (no: 15), cell parameters are a=13.3535(9) Å, b=6.3859(7) Å, c=19.1940(19) Å, β=101.75(3)°, V=1602.5(3) Å³ and Z=4. It has been proven that the nicotinamide ligands in the structure of the Zn(II) complex are coordinated to the metal ion with N atoms ([ZnBr₂(na)₂] where na: nicotinamide).     

Synthesis and structural characterization of cobalt(II) and zinc(II) complexes with 2-(indazol-1-yl)-2-thiazoline (TnInA). X-ray characterization of [CoCl2(TnInA)2] · C2H6O and [(M)(TnInA)2(H2O)2](NO3)2 (M = Co, Zn)

Several complexes of 2-(indazol-1-yl)-2-thiazoline (TnInA) with the divalent ions Co and Zn have been synthesized by the direct combination of the ligand and the metal chloride or nitrate hydrated salts in ethanol. These complexes have been characterized by a variety of physical–chemical techniques. Moreover, the structures of [CoCl₂(TnInA)₂] · C₂H₆O (1) and [(M)(TnInA)₂(H₂O)₂](NO₃)₂ (M = Co, 3; Zn, 4) were determined by single-crystal X-ray diffraction. In all the complexes, the ligand TnInA bonds to the metal ion through the indazole and thiazoline nitrogen atoms. In complex 1 the environment around the cobalt ion may be described as a distorted octahedron with two TnInA ligands and two chlorine ligands. Compounds 3 and 4 are isostructural with a distorted octahedral geometry around the metal center, being linked to two water molecules and two TnInA ligands. However, in complex [ZnCl₂(TnInA)] (2) the zinc atom is four-coordinated with a probable tetrahedral environment with two chloro ligands and one TnInA ligand bonded to the metal ion.     

Pure and doped lanthanum cobaltites obtained by combustion method

We report the synthesis of La_1−xSr_xCoO₃ nanopowders by solution combustion method using metal nitrates and -alanine (alanine method) or urea (urea method) as fuel. The influence of metal nitrates/organic substance molar ratio and the type of fuel was investigated. The isolated complex precursors were characterized by atomic absorption spectroscopy (AAS), FT-IR spectra and DTA–TG analysis. The La_1−xSr_xCoO₃ (x = 0–0.3) powders were characterized by X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive X-ray analysis (SEM–EDX), as well as by specific surface area measurements. XRD patterns indicate the formation of single-phase LaCoO₃ (rhombohedral) when as-synthesized powders were calcined at 873 K, 3 h in the case of the alanine method and at 1073 K, 3 h for urea-based system. Also, strontium doped lanthanum cobaltites obtained by both methods at 1273 K are single phase with rhombohedral perovskite-like structure as XRD data have proved. SEM investigation of pure and doped lanthanum cobaltites reveal that the samples prepared by both methods have fine particles with tendency of agglomerates formation with different shapes, spongy aspect and high porosity. La_1−xSr_xCoO₃ nanopowders obtained by alanine method have larger specific surface area values than those prepared by urea method.     

Spectroscopic properties of K5Li2UF10

A new uranium (III) fluoro-complex of the formula K₅Li₂UF₁₀ has been synthesised and characterised by X-ray powder diffraction and electronic absorption spectra measurements. The compound crystallises in the orthorhombic system, space group Pnma, with a = 20.723, b = 7.809, c = 6.932 Å, V = 1121.89 ų, Z = 4 and is isostructural with its K₅Li₂NdF₁₀ and K₅Li₂LaF₁₀ analogous. The absorption spectrum of a polycrystalline sample of K₅Li₂UF₁₀ was recorded at 4.2 K in the 3500–45,000 cm⁻¹ range and is discussed. The observed crystal-field levels were assigned and fitted to parameters of the simplified angular overlap model (AOM) and next to those of a semi-empirical Hamiltonian, which was representing the combined atomic and one-electron crystal-field interactions. The starting values of the AOM parameters were obtained from ab initio calculations. The analysis of the spectra enabled the assignment of 71 crystal-field levels of U³⁺ with a relatively small r.m.s. deviation of 37 cm⁻¹. The total splitting of 714 cm⁻¹ was calculated for the ⁴I_9/2 ground multiplet.     

An investigation on the solid state pyrolytic decomposition of bimetallic oxalate precursors of Ca, Sr and Ba with cobalt: A mechanistic approach

The mixed metal oxalate precursors, calcium(II)bis(oxalato)cobaltate(II)hydrate (COC), strontium(II)bis(oxalato)cobaltate(II)pentahydrate (SOC) and barium(II)bis(oxalato)cobaltate(II)octahydrate (BOC) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR spectral and X-ray powder diffraction studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound COC decomposed mainly to CaC₂O₄ and Co₃O₄ at 340 °C, and a mixture of CaCO₃ and Co₃O₄ identified at 510 °C. A mixture of CaCO₃ and Ca₃Co₂O₆ along with the oxides and carbides of both the cobalt and calcium were attributed at 1000 °C as end products. DSC study in nitrogen ascertained the formation of a mixture of CaO and CoO along with a trace of carbon at 550 °C. The mixture species, SrC₂O₄, CoC₂O₄ and Co₃O₄ were generated at 255 °C in case of SOC in air, which ultimately changed to CoSrO₃, SrCO₃ and oxides of strontium and cobalt at 1000 °C. The several mixture species also generated as intermediate at 332 and 532 °C. The DSC study in nitrogen indicated the formation of CoSrO_x (0.5 < x < 1) as end product. In case of BOC in air, a mixture of BaCoO₂, BaO, CoO and carbides are identified as end product at 1000 °C through the generation of several intermediate species at 350 and 530 °C. A mixture of BaO and CoO is identified as end product in DSC study in nitrogen. The kinetic parameters have been evaluated for all the dehydration and decomposition steps of all the three compounds using four non-mechanistic equations. Using seven mechanistic equations, the kind of dominance of kinetic control mechanism of the dehydration and decomposition steps are also inferred. The kinetic parameters, ΔH and ΔS of all the steps are explored from the DSC studies. Some of the decomposition products are identified by IR and X-ray powder diffraction studies.     

Tautomeric properties, conformations and structure of N-(2-hydroxyphenyl)-4-amino-3-penten-2-on

N-(2-hydroxyphenyl)-4-amino-3-penten-2-on (C₁₁H₁₃NO₂) has been studied by X-ray analysis. It crystallizes the orthorhombic space group P2₁2₁2₁ with a=8.834(1), b=10.508(2), c=11.212(2) Å, V=1040.8(3) Å³, Z=4, D_c=1.22 g cm⁻³ and μ(MoK)=0.084 mm⁻¹. The structure was solved by direct methods and refined to R=0.038 for 1373 reflections (I>2σ(I)). The title compound is photochromic and the molecule is not planar. Intramolecular hydrogen bonds occur between the pairs of atoms N(1) and O(1) [2.631(2) Å], and N(1) and O(2) [2.641(2) Å], the H atom essentially being bonded to the N atom. There is also a strong intermolecular O–HO hydrogen bonding [2.647(2) Å] between neighbouring molecules. Tautomeric properties and conformations of the title compound were investigated by semi-empirical quantum mechanical AM1 calculations and the results are compared with the X-ray results.     

Plasma chemical preparation and characterization of perovskite-type mixed oxides

The microwave plasma enhanced chemical vapour deposition (MPECVD) was applied for the preparation of perovskite-like mixed oxides, using either the metal acetylacetonates or metal nitrates as precursors. The same materials were prepared by the citrate method as reference substances. The obtained mixed oxides were calcined at 1100 °C, tested in the methane oxidation up to 1000 °C and characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma–optical emissions spectroscopy (ICP–OES) and specific surface area (BET) determination. These studies revealed that LaMnO₃ with La³⁺ cation partly substituted by Sr, Ce and Ba cations and La_0.9Sr_0.1Co_0.9Fe_0.1O₃ calcined at 1100 °C seem to be highly active and stable catalysts in methane oxidation. In the case of LaMnO₃ and La_0.9Ce_0.1MnO₃ lowest light-off temperatures were reached with the catalysts prepared by the plasma method.     

Soft chemistry synthesis of the perovskite CaCu3Ti4O12

The perovskite CaCu₃Ti₄O₁₂ (CCT) has been obtained after calcination of oxalate precursors at 900–1000 °C in air. Those precursors are prepared using a soft chemistry method, the coprecipitation. The oxalate powders consist of disk-like particles of 2–3 μm diameter and 300–400 nm thickness. By varying the ratio of the initial amounts of metal chlorides, additional phases (CaTiO₃, TiO₂ and CuO) could be obtained besides CCT. The corresponding multiphased ceramics present improved dielectric properties.     

Synthesis and characterisation of Hf(thd)2X2 derivatives [X = N(SiMe3)2, OSiMe3 and OSiBuMe2] as precursors for MOCVD of hafnium silicate films

Hafnium β-diketonatochlorides HfCl₂(thd)₂ (1), HfCl(thd)₃ (2) as well as β-diketonato-silylamide and/or siloxide derivatives of 1 namely Hf(thd)₂[N(SiMe₃)₂]₂ (3), Hf(thd)₂(OSiMe₃)₂ (4) and Hf(thd)₂(OSi^tBuMe₂)₂ (5) (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) were synthesized and characterized by elemental analysis, FT-IR, ¹H NMR and TGA. 2 and 5 were also characterized by single-crystal X-ray diffraction. The siloxide ligands are in cis position for 5 and exert a strong trans effect. The new volatile compounds were tested as single-source precursors for the deposition of HfSi_xO_y films by pulsed liquid injection MOCVD on Si(1 0 0) and R plane sapphire. The as-deposited at 600–800 °C films were essentially amorphous, Hf-rich (Hf/Hf + Si = 0.7–0.85) and smooth.     

Sintering behavior and apatite formation of diopside prepared by coprecipitation process

Sintering behavior and bioactivity of diopside, CaMgSi₂O₆, prepared by a coprecipitation process were examined for its biomedical applicability. As-prepared powder was synthesized by adding aqueous ammonia to an ethanol solution containing Ca(NO₃)₂·4H₂O, Mg(NO₃)₂·6H₂O, and Si(OC₂H₅)₄ and characterized by means of TG–DTA, XRD, and TG–MS. The dried powder was X-ray amorphous and crystallized into diopside at 845.5 °C. The glass network formation by SiO₄ tetrahedra was almost completed below 800 °C. The bioactivity of the diopside prepared by sintering the compressed powder at 1100 °C for 2 h was evaluated by immersion of the sintered body in a simulated body fluid (SBF) at 36.5 °C. Leaf-like apatite particles were found to be formed on the surface of the sintered body and grew with passage of soaking time. This apatite-forming behavior in the SBF is related to the dissolution of Ca(II) ions from the sintered body in the early stage of immersion. Thus, diopside prepared by the coprecipitation process using the metal alkoxide and the metal salts was found to have an apatite-forming ability.     

Aqueous guanidinium salts: Part II. Isopiestic osmotic coefficients of guanidinium sulphate and viscosity and surface tension of guanidinium chloride, bromide, acetate, perchlorate and sulphate solutions at 298.15 K

The molality dependence of isopiestic osmotic coefficients of aqueous guanidinium sulphate, Gn₂SO₄ has been reported at 298.15 and analysed by the Pitzer equations. The Pitzer coefficients obtained from the analysis of osmotic coefficients are employed to calculate the activity coefficients. The viscosity and surface tension of aqueous guanidinium chloride (GnCl), bromide (GnBr), acetate (CH₃COOGn), perchlorate (GnClO₄) and sulphate (Gn₂SO₄) have also been measured at 298.15 K. The order in which these salts increase the viscosity and surface tension of water is: Gn₂SO₄>CH₃COOGn>GnCl>GnBr>GnClO₄. The effect of Gn₂SO₄ and CH₃COOGn on the viscosity and surface tension is stronger than that of other guanidinium salts.     

Dilatometric and high temperature X-ray diffractometric studies of La1−xMxCrO3 (M=Sr, Nd, x=0.0, 0.05, 0.10, 0.20 and 0.25) compounds

The phase transition, bulk and lattice thermal expansion behaviour of the strontium and neodymium substituted lanthanum chromites have been studied by dilatometry and high temperature X-ray powder diffractometry from room temperature to 1123 and 1073 K, respectively, in static air. The studies revealed that the temperature of the orthorhombic to rhombohedral phase transition, which occurred at 550 K in undoped LaCrO₃, decreased on substitution of Sr²⁺ ions and increased on substitution of Nd³⁺ ions, systematically. However, the coefficients of average linear and volume thermal expansion (_l and _v) of LaCrO₃ showed a marginal increase on Sr²⁺ substitution to different extent, whereas a reverse trend was observed with Nd³⁺ substitution. The phase transition temperatures and _l and _v of the compounds as determined by dilatometric and high temperature X-ray diffractometric methods are reported.     

Phosphomolybdic acid supported on silica gel and promoted with alkali metal ions as catalysts for the esterification of acetic acid by ethanol

Different ratios of phosphomolybdic acid PMA supported on silica gel (1–30 wt%) and promoted with alkali metal hydroxide have been prepared by an impregnation method and calcinated at 350 °C for 4 h. The catalysts were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction, FT-IR spectroscopy and N₂ adsorption measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration–dehydrogenation of 2-propanol. The gas-phase esterification of acetic acid by ethanol was carried out in a conventional flow bed reactor. The results clearly revealed that among the PMA loading, the use of 10 wt% catalyst showed maximum yield of ethyl acetate. This catalyst also improved on addition of Na or K-hydroxide. These results were correlated with the structure and the acid–base properties of the prepared catalysts.     

Synthesis, structure and theoretical study of two rhodium(I) complexes [Rh(TropNMe)(CO)(PPh3)] and [Rh(Trop)(CO)(PPh3)] · Acetone

Rhodium(I) complexes [Rh(TropNMe)(CO)(PPh₃)] (TropNMe = 2-(N-methylamino)tropone, ONC₈H₉) (1) and [Rh(Trop)(CO)(PPh₃)] · Acetone (Trop = Tropolone, O₂C₇H₆) (2) have been synthesized and characterized by single-crystal X-ray diffraction analysis. A distorted square planar geometry about the rhodium(I) metal centre is observed in both compounds 1 and 2. Substitution of an oxygen atom with a methyl functionalized nitrogen atom does not significantly alter the bond distances and angles in the rhodium(I) complex. A theoretical study at B3LYP/6-31G(d) (main group) and LANL2DZ (Rh) level is presented to clarify the solid state behaviour of these complexes.     

Structures of 3,3′-dicarbometoxy-2,2′-bipyridine complexes with silver(I) and copper(II) cations

The structures of 3,3′-dicarbometoxy-2,2′-bipyridine (dcmbpy) complexes with copper(II) and silver(I) cations have been determined using single crystal X-ray-diffraction. The crystals of Cu(dcmbpy)Cl₂ are monoclinic, C2/c, a = 16.966(3), b = 18.373(3), c = 13.154(2) Å, β = 126.543(3)°. The crystals of Ag(dcmbpy)NO₃ · H₂O are also monoclinic, C2/c, a = 16.7547(13), b = 11.0922(9), c = 18.7789(18) Å, β = 100.228(7)°. The results have been compared with the literature data on the complexes of dcmbpy and its precursors: 2,2′-bipyridine (bpy) and 3,3′-dicarboxy-2,2′-bipyridine (dcbpy). Two types of complexes of 3,3′-carboxy derivatives of bpy are distinguished: (1) with metal atom bonded to two N atoms of the same molecule and (2) with metal atom bonded to two N atoms of two different molecules. The Cu(dcmbpy)Cl₂ complex belongs to the first type, whereas Ag(dcmbpy)NO₃ · H₂O belongs to the second type.     

Synthesis and characterization of uranium(III) compounds supported by the hydrotris(3,5-dimethyl-pyrazolyl)borate ligand: Crystal structures of [U(Tp)2(X)] complexes (X = OC6H2-2,4,6-Me3, dmpz, Cl)

Reaction of [U(Tp^Me2)₂(NR₂)] (R = Ph, SiMe₃) with protic substrates such as 2,4,6-trimethylphenol (HOC₆H₂-2,4,6-Me₃), 3,5-dimethylpyrazole (Hdmpz), 2-mercaptopyridine (HSC₅H₄N) and phenylacetylene (HCCPh) afforded the corresponding [U(Tp^Me2)₂(OAr)] (Ar = C₆H₂-2,4,6-Me₃) (1), [U(Tp^Me2)₂(dmpz)] (2), [U(Tp^Me2)₂(η²-SC₅H₄N)] (3), and [U(Tp^Me2)₂(CCPh)] (4) compounds. Reaction of [U(Tp^Me2)₂(NR₂)] with Me₃SnCl or Me₃SiBr gave [U(Tp^Me2)₂Cl] (5) and [U(Tp^Me2)₂Br] (6), respectively, in high yield. The amido precursors failed to react with cyclopentadiene, but metathesis of [U(Tp^Me2)₂I] with NaCp yielded [U(κ³-Tp^Me2)(κ²-Tp^Me2)(η⁵-Cp)] (7). Thermolysis of 7 resulted in oxidation of the metal centre and redistribution of the ligands, giving [UCp₃(dmpz)] (8), pyrazabole (9) and [U(Tp^Me2)(dmpz)₃] (10). The complexes have been fully characterized by spectroscopic methods and the structures of 1, 2, and 5 were confirmed by X-ray crystallographic studies. In the solid state the complexes exhibit distorted pentagonal bipyramidal geometries.     

Neutral pyridylmethylamide ligands and their mononuclear copper(II) complexes

Mononuclear copper(II) complexes of a family of pyridylmethylamide ligands HL, HL^Me, HL^Ph, HL^Me3 and HL^Ph3, [HL = N-(2-pyridylmethyl)acetamide; HL^Me = N-(2-pyridylmethyl)propionamide; HL^Ph = 2-phenyl-N-(2-pyridylmethyl)acetamide; HL^Me3 = 2,2-dimethyl-N-(2-pyridylmethyl)propionamide; HL^Ph3 = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide], were synthesized and characterized. The reaction of copper(II) salts with the pyridylmethylamide ligands yields complexes [Cu(HL)₂(OTf)₂] (1), [Cu(HL^Me)₂](ClO₄)₂ (2), [Cu(HL)₂Cl]₂[CuCl₄] (3), [Cu(HL^Me3)₂(THF)](OTf)₂ (4), [Cu(HL^Me3)₂(H₂O)](ClO₄)₂ (5a and 5b), [Cu(HL^Ph3)₂(H₂O)](ClO₄)₂ (6), [Cu(HL)(2,2′-bipy)(H₂O)](ClO₄)₂ (7), and [Cu(HL^Ph)(2,2′-bipy)(H₂O)](ClO₄)₂ (8). All complexes were fully characterized, and the X-ray structures vary from four-coordinate square-planar, to five-coordinate square-pyramidal or trigonal-bipyramidal. The neutral ligands coordinate via the pyridyl N atom and carbonyl O atom in a bidentate fashion. The spectroscopic properties are typical of mononuclear copper(II) species with similar ligand sets, and are consistent their X-ray structures.     

Synthesis of spherical nanoparticles of Cu2L2O5 (L=Ho, Er) from W/O microemulsions

Nanoparticles of Cu₂L₂O₅ (L=Ho, Er) (15–25 nm in size) were synthesised by the intermediate use of W/O microemulsions. In this process the aqueous cores of water/cetyltrimethylammonium bromide/n-octane/1-butanol microemulsions were used as microreactors for the precipitation of Cu₂Ho₂(CO₃)₄(OH)₂ (25–30 nm) and Cu₂Er₂(CO₃)₄(OH)₂ (10–40 nm) as precursors. These mixed salts were separated and further decomposed to the corresponding mixed oxides at 900°C for 16 h. All solids were characterised by scanning and transmission electron microscopy, IR, XRPD, ICP-OES, TGA, XPS measurements and elemental analyses.     

Tautomeric properties, conformations and structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine

The crystal structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine (C₁₃H₁₀NO₂Cl) was determined by X-ray analysis. It crystallizes orthorhombic space group P2₁2₁2₁ with a=12.967(2) Å, b=14.438(3) Å, c=6.231(3) Å, V=1166.5(6) Å³, Z=4, D_c=1.41 g cm⁻³ and μ(MoK)=0.315 mm⁻¹. The title compound is thermochromic and the molecule is nearly planar. Both tautomeric forms (keto and enol forms in 68(3) and 32(3)%, respectively) are present in the solid state. The molecules contain strong intramolecular hydrogen bonds, N1–H1O1/O2 (2.515(1) and 2.581(2) Å) for the keto form and O1–H01N1 for the enol one. There is also strong intermolecular O2–HO1 hydrogen bonding (2.599(2) Å) between neighbouring molecules. Minimum energy conformations AM1 were calculated as a function of the three torsion angles, θ₁(N1–C7–C6–C5), θ₂(C8–N1–C7–C6) and θ₃(C9–C8–N1–C7), varied every 10°. Although the molecule is nearly planar, the AM1 optimized geometry of the title compound is not planar. The non-planar conformation of the title compound corresponding to the optimized X-ray structure is the most stable conformation in all calculations.     

Performance of Pt/SnO2 catalyst in the gas phase hydrogenation of crotonaldehyde

Selective hydrogenation of crotonaldehyde was performed on 5% Pt/SnO₂ catalysts, in gaseous phase, at atmospheric pressure, at 353 K. Two types of catalyst were prepared using H₂PtCl₆ and Pt(NH₃)₄(NO₃)₂ as metallic precursors. Their performances were compared as a function of the reduction temperature and both catalysts were characterised by X-ray diffraction after different reduction treatments. Using the ex-chloride catalyst, the selectivity values to the unsaturated alcohol (UOL) resulted into a maximum of 45% while a selectivity as high as 70–77%, in 0–25% conversion range, was achieved by using ex-nitrate catalyst reduced at 443 K. The formation of Pt–Sn alloy on the metal particles of platinum was thought to be necessary to improve the activity and the selectivity on these catalysts. In the contrast, a presence of PtSn₂ formed at a reduction temperature higher than 473 K led to a decrease of activity and selectivity.