Thermal decomposition kinetics of lanthanum and neodymium bromide complexes with glycine or alanine

Four complexes of rare earth bromides with amino acids, REBr₃·3L·3H₂O (RE=La, Nd;L=glycine or alanine) were prepared and characterized by means of chemical analysis, elemental analysis, molar conductivity, thermogravimetry, IR spectra and X-ray diffraction. Their thermal decomposition kinetics from ambient temperature to 500°C were studied by means of TG-DTG techniques under non-isothermal conditions. The kinetic parameters (activation energyE and pre-exponential constantA) and the most probable mechanisms of thermal decomposition were obtained by using combined differential and integral methods. The thermal decomposition processes of these complexes are distinguished as being of two different types, depending mainly on the nature of the amino acid.     

Solid–liquid equilibria of the ternary system m-nitrobenzoic acid + p-nitrobenzoic acid + acetone

Solubility data and the density of equilibrium liquid phase for the ternary system m-nitrobenzoic acid + p-nitrobenzoic acid + acetone were determined at 283.1 K and 313.1 K, and the phase diagrams of the system were constructed. Two solid phases, pure solid m-nitrobenzoic acid and p-nitrobenzoic acid are confirmed by the Schreinemaker's wet residue method. The crystallization regions of m-nitrobenzoic acid and p-nitrobenzoic acid increase as the temperature decreases. At the same temperature, the crystallization region of p-nitrobenzoic acid is larger than that of m-nitrobenzoic acid.     

Eyring parameters of dehydration processes

Thermogravimetry was used in the study of the kinetics of dehydration of MnSO₄·5H₂O, CuSO₄·5H₂O and 3CdSO₄·8H₂O under static air atmosphere. The values of the kinetic and thermodynamic parameters for each stage of thermal dehydration were calculated from α(T) data by using the integral method, applying the Coats-Redfern approximation. The best model for all stages of dehydration is random nucleation model F1. The dependencies of enthalpy on entropy of activated complexes for different kinetic models were described. The linear relation was calculated between the Gibbs energy of activated complexes and the maximum dehydration rate temperature for analysed dehydration processes.     

Oxalate-2-ethanolamine complexes of some bivalent cations (Mn,Co, Ni,Cu, Zn and Cd)

On the refluxing ofM(II) oxalate (M=Mn, Co, Ni, Cu, Zn or Cd) and 2-ethanolamine in chloroform, the following complexes were obtained: MnC₂O₄·HOCH₂CH₂NH₂·H₂O, CoC₂O₄·2HOCH₂CH₂NH₂, Ni₂(C₂O₄)₂·5HOCH₂CH₂NH₂·3H₂O, Cu₂(C₂O₄)₂·5HOCH₂CH₂NH₂, Zn₂(C₂O₄)₂·5HOCH₂CH₂NH₂·2H₂O and Cd₂(C₂O₄)₂·HOCH₂CH₂NH₂·2H₂O. Following the reaction ofM(II) oxalate with 2-ethanolamine in the presence of ethanolammonium oxalate, a compound with the empirical formula ZnC₂O₄·HOCH₂CH₂NH₂·2H₂O¹ was isolated. The complexes were identified by using elemental analysis, X-ray powder diffraction patterns, IR spectra, and thermogravimetric and differential thermal analysis. The IR spectra and X-ray powder diffraction patterns showed that the complexes obtained were not isostructural. Their thermal decompositions, in the temperature interval between 20 and about 900°C, also take place in different ways, mainly through the formation of different amine complexes. The DTA curves exhibit a number of thermal effects.     

Preparation et caracterisation de complexes [cis-4,4′-dinitrodibenzo-18-couronne-6, LnCl3, 3CH3CN]

Some new complexes between thecis-4,4′-dinitrodibenzo-18-crown-6 and rare earth chlorides LnCl₃ (Ln=Nd, Gd, Yb) were synthesized in acetonitrile. Ligandcis-4,4′-dinitrodibenzo-18-crown-6 and its complexes were identified by infrared spectroscopy, X-ray diffraction and thermal analysis (TG and DTA). Acis-trans isomerisation of the complexed ligand is observed about 148°C when heating the rare earth complex.

     

On the relationship between the structures of Cu(II) complexes and their chemical transformations

The thermal dehydration of pentacoordinate complexes [Cu(maleinate)(H₂O)] (I), [Cu₂(citrate) (H₂O)₂] (II) and [Cu(phenoxyacetate)₂(H₂O₃] (III) was investigated and correlated with the structural changes occurring during the dehydration. It was found that the activation parameters of the reactions do not follow the lengths of the split Cu?OH₂ bonds. The lowestE _a and lgA values were found for compound I, the highest ones for compound III. The most expressive changes of the anionic ligand binding mode take place during the dehydration of this compound.     

Design and synthesis of coordination networks containing amide,pyridine and carboxylate functionalities

The reactions of bis(pyridinecarboxamido)alkane with copper(II) in the presence of mono or dicarboxylic acids resulted in discrete species, one-dimensional and two-dimensional networks. The carboxylates considered for this study include m-nitrobenzoic acid, isophthalic acid and succinic acid. In the presence of m-nitrobenzoic acid the ligands with Cu(II) form 1D coordination networks which include m-nitrobenzoic acid and water molecules as guests. The use of isophthalic acid resulted in discrete species while the use of succinic acid resulted in a two-dimensional layer containing rectangular grids of dimension 9.7 × 16.5 Å². The 2D layers in this complex exhibit inclined 2-fold interpenetration. Further, all these coordination networks are assembled via hydrogen bonding interactions between the amides and water molecules. The Cu(II) centre exhibits a unique octahedral coordination geometry, for the complexes reported here, as it coordinates with two each of pyridine moieties, water molecules and carboxylates.     

Rare earth phosphate powders RePO4·nH2O (Re=La,Ce or Y) II. Thermal behavior

The thermal behavior, thermostructural and morphological changes, of rare earth phosphate powders RePO₄·nH₂O (Re=La, Ce or Y) was investigated up to 1500°C using high temperature X-ray diffraction, FT-infrared and Raman spectroscopies and thermogravimetry coupled with differential thermal analysis. The hydration water of the compounds was zeolitic (for Re=La or Ce) or coordinated (for Re=Y) and was associated with a divariant or a monovariant equilibrium of dehydration, respectively. The high temperature anhydrous monoclinic phase LaPO₄ or CePO₄ formed irreversibly at about 750°C after the total dehydration of the hexagonal hydrated structure while the dehydration of the monoclinic YPO₄·2H₂O phase began from about 190°C with its simultaneous decomposition into tetragonal YPO₄. A polytrioxophosphate secondary minor phase Re(PO₃)₃ resulting from adsorbed H₃PO₄ was formed at 950°C and decomposed at 1350°C. The particle morphology did not change with the temperature but grain coalescence occurred below 1000°C.     

Synthesis and characterisation of Co(II), Ni(II), Zn(II) and Cd(II) complexes with 5-bromo-N,N′-bis-(salicylidene)-o-tolidine

New complexes of type [M(HL)(CH₃COO)(OH₂)_m]·nH₂O (where M:Co, m = 2, n = 2; M:Ni, m = 2, n = 1.5; M:Zn, m = 0, n = 2.5 and M:Cd, m = 0, n = 0; H₂L:5-bromo-N,N′-bis-(salicylidene)-o-tolidine) have been synthesized and characterized by microanalytical, IR, UV–Vis-NIR and magnetic data. Electronic spectra of Co(II) and Ni(II) complexes are characteristic for an octahedral stereochemistry. The IR spectra indicate a chelate coordination mode for mono-deprotonated Schiff base and a bidentate one for acetate ion. The thermal transformations are complex according to TG and DTA curves including dehydration, acetate decomposition and oxidative degradation of the Schiff base. The final product of decomposition is the most stable metallic oxide.     

Heat capacity and thermodynamical properties of the crystal of [RE2(Glu)2(H2O)8](ClO4)4·H2O (RE = Nd, Eu, Dy)

Thermodynamical data of rare earth complexes with amino acid are important for engineering chemistry and fundamental chemistry. However, they have rarely been reported. In this work, a series of crystalline complexes of rare earth perchlorate coordinated with glutamic acid have been synthesized in water medium, and their thermodynamical data, including the heat capacity in low temperature range and the standard enthalpy of formation, were determined. These complexes were identified to be [RE₂(Glu)₂(H₂O)₈](ClO₄)₄·H₂O (RE = Nd, Eu, Dy) by using thermogravimetric analysis (TG), differential thermal analysis (DTA), and chemical and elementary analyses. Their purity has been determined. No melting points were observed for all the three complexes. The heat capacity of the complexes was measured by an adiabatic calorimeter from 79 to 370 K. Abnormal heat capacity values were detected for two of the complexes and the decomposition range of one complex was found. The temperature, enthalpy change and entropy change of the decomposition processes of the three complexes were calculated. The polynomial equations of heat capacity in the experimental temperature range have been obtained by least squares fitting. The standard enthalpy of formation was determined by an isoperibol reaction calorimeter at 298.15 K. Supported by the Research Fund of Beijing Institute of Petro-Chemical Technology (N06-06)     

Thermal decomposition reaction kinetics of complexes of [Sm(o-MOBA)3bipy]2·H2O and [Sm(m-MOBA)3bipy]2·H2O

The complexes of [Sm(o-MOBA)₃bipy]₂·H₂O and [Sm(m-MOBA)₃bipy]₂·H₂O (o(m)-MOBA = o(m)-methoxybenzoic acid, bipy-2,2′-bipyridine) have been synthesized and characterized by elemental analysis, IR, UV, XRD and molar conductance, respectively. The thermal decomposition processes of the two complexes were studied by means of TG–DTG and IR techniques. The thermal decomposition kinetics of them were investigated from analysis of the TG and DTG curves by jointly using advanced double equal-double steps method and Starink method. The kinetic parameters (activation energy E and pre-exponential factor A) and thermodynamic parameters (ΔH ^≠ , ΔG ^≠ and ΔS ^≠) of the second-step decomposition process for the two complexes were obtained, respectively.     

Oxidation of nitrotoluenes with air using N-hydroxyphthalimide analogues as key catalysts

Nitrotoluenes are efficiently oxidized with air to the corresponding nitrobenzoic acids by the use of N-acetoxyphthalimide (NAPI) as a key catalyst. Thus, p- and m-nitrotoluenes under 10 atm of air in the presence of NAPI combined with Co(OAc)₂ (0.5 mol%) and Mn(OAc)₂ (0.05 mol%) at 130°C afforded p- and m-nitrobenzoic acids in 81 and 92% yields, respectively. o-Nitrotoluene was oxidized to o-nitrobenzoic acid in 51% yield by the aid of NO₂.     

Studies on some oxovanadium(IV) complexes of acyl pyrazolone analogues

A series of novel bidentate pyrazolone based Schiff base ligands were synthesized by interaction of 4-benzoyl-3-methyl-1-(4′-methylphenyl)-2-pyrazolin-5-one with various aromatic amines like aniline, o-,m-,p-chloroaniline and o-,m-,p-toluidine in a ethanolic medium. All of these ligands have been characterized on the basis of elemental analysis, IR and ¹H NMR data. The molecular geometries of five of these ligands have been determined by single crystal X-ray study. Crystallographic study reveals that these ligands exist in the amine-one tautomeric form in the solid state. NMR study also suggests the existence of the amine-one form in solution at room temperature. Ab initio calculations for representative ligand HL¹ has been carried out to know the coordination site of the ligand. Novel vanadium Schiff base complexes of these ligands with general formula [OV(L^1–7)₂(H₂O)] have been prepared by interaction of aqueous solution of vanadyl sulfate pentahydrate with DMF solution of the appropriate ligands. The resulting complexes have been characterized on the basis of elemental analysis, vanadium determination, molar conductance and magnetic measurements, thermo gravimetric analysis, infrared and electronic spectral studies. Suitable distorted octahedral structures have been proposed for these complexes.     

Unexpected Formation of the Mixed Ligand Complexes [Cu(OAc)(bipy)2]Cl·4H2O·1/2MeOH and [Co(OH2)2(phen)2](OAc)2·6H2O,and their Crystal Structures

The mononuclear compounds [Cu(OAc)(bipy)₂]Cl·4H₂O·1/2MeOH( 1 ) and [Co(OH₂)₂(phen)₂](OAc)₂·6H₂O( 2 ) were unexpectedly obtained as single crystals from mother liquors left following isolation of the expected products of the reactions, in ethanol of Cu(OAc)₂, benzylic acid and 2, 2'‐bipyridine (for 1 ) and Co(OAc)₂, D, L‐mandelic acid and 1, 10‐phenanthroline (for 2 ). The complexes were characterized by elemental analysis, IR and electronic spectroscopy and magnetic measurements at room temperature and their structures were determined by single‐crystal X‐ray analysis. In 1 , the pentacoordinated copper atom has a basically square pyramidal coordination polyhedron, while in 2 the cobalt atom has a distorted octahedral environment. In both cases, the complexes are linked by hydrogen bonds and aromatic‐aromatic interactions.     

Chemistry of thorium : Volumetric determination of thorium

Thorium has been determined volumetrically. It has been precipitated with m-nitrobenzoic acid according to the method of Neish. Thorium m-nitrobenzoate has been then dissolved in sulphuric acid and titrated with titanous chloride to determine the NO₂-group which gives the amount of thorium directly.     

Influence of solvent environment using the CPCM model on the H-bond geometry in the complexes of phosphorus acids with DMSO

Quantum chemical calculations of structure and energies of various H-bonded complexes of phosphoric, phosphorous and methylphosphonic acids and their dimers with dimethylsulfoxide (DMSO), i.e., (acid) _n –DMSO and acid–(DMSO) _m for n = 1, 2 and m = 2, 3 have been carried out. The polar solvent effect is taken into account by using the CPCM model. It has been found that in DMSO environment the H-bonds in all complexes of investigated acid with DMSO are sizably stronger than the ones in the gas phase. At B3LYP-CPCM computation, the H-bonds between all investigated acid dimers and DMSO are significantly shorter than those found for complexes of corresponding acids with other compositions. The H-bonding interaction in acid–(DMSO) _m for m = 1–3 becomes slightly weaker with increasing number DMSO molecules. The strength of the H-bond in all investigated complexes increases in the series of acids: (HO)₂MePO < (HO)₂P(O)H < H₃PO₄. Additionally, quantum theory of ‘atoms in molecules’ and natural bond orbitals method have been applied to analyze H-bond interactions.     

混合配体、希土三元配合物的研究 Ⅳ.3,5二硝基水扬酸(H2DNSA)、邻菲咯啉(phen)、希土(RE)三元固体配合物的合成及性质

本文报道了十种希土元素与3,5-二硝基水扬酸、邻菲咯啉三元配合物的制备方法。通过元素和化学分析测定了化合物的化学组成,并用红外光谱、紫外光谱、差热分析、磁化率、X射线粉天衍射等对所合成的化合物进行了结构和性质的研究。     

Oxidation of 4-nitro-<Emphasis Type="Italic">o</Emphasis>-xylene with nitric acid using <Emphasis Type="Italic">N</Emphasis>-hydroxyphthalimide under phase transfer conditions

4-Nitro-o-xylene was selectively oxidized to 2-methyl-4-nitrobenzoic acid using dilute nitric acid as the oxidizing agent under atmospheric pressure. The oxidation of 4-nitro-o-xylene was effectively promoted by an addition of radical initiators. Under reflux, 2-methyl-4-nitrobenzoic acid was afforded in high yield using nitric acid combined with N-hydroxyphthalimide, cobalt dichloride (CoCl₂ · 6H₂O), manganese acetate (Mn(OAc)₂ · 4H₂O) and phase transfer catalyst.     

Thermal decomposition of scandium(III) 2-chloro-, 30chloro, 4-chloro- and 2,4-dichlorobenzoates in an air atmosphere

The conditions of thermal decomposition of hydrated scandium(III) chlorobenzoates were studied. On heating, the carboxylates decompose in many steps. The hydrated complexes first lose water of crystallization in one or two steps and then anhydrous compounds are transformed to Sc₂O₃ with formation of Sc₂O(CO₃)₂ intermediate. The dehydration of the complexes is accompanied by an endothermic effect and the decomposition of anhydrous complexes by strong endothermic effects. The anhydrous complexes are melted at 255–300°C.     

Synthesis and characterization of zinc benzoate complexes through combined solid and solution phase reactions

A combined solid and solution phase methodology for the synthesis of a series of mononuclear and polynuclear zinc benzoate complexes is described. The substituent on the aromatic ring and the effect of solvent on deciding the composition of the complexes is presented. From the 4-substituted benzoic acids 4-methylbenzoic acid (ptolH), 4-nitrobenzoic acid (pnitrobenH) and 4-chlorobenzoic acid (pchlorbenH), the mononuclear complexes [Zn(ptol)₂(H₂O)₂], [Zn(pnitroben)₂(H₂O)(DMSO)₂] and [Zn(pchlorben)₂py)₂] (where DMSO = dimethylsulfoxide, py = pyridine) have been synthesized and structurally characterised. Zinc complexes from the reaction of zinc sulfate heptahydrate with 3-methylbenzoic acid (mtolH) and 2-methylbenzoic acid (otolH), the dinuclear complexes [Zn₂(μ²-mtol)₄(py)₂], [Zn₂(μ²-otol)₄(py)₂], pentanuclear complex [Zn₅(μ²-mtol)₆(mtol)₂(μ³-OH)₂ (py)₂] and tetranuclear complex [Zn₄(μ²-otol)₆(μ⁴-O) (DMSO)₂], have been prepared by varying the reaction conditions and the complexes have been structurally characterized.