Characterization of the decomposition course of nickel acetate tetrahydrate in air

Thermogravimetry, differential thermal analysis, X-ray diffractometry and infrared spectroscopy showed that Ni(CH₃COO)₂·4H₂O decomposes completely at 500°C, giving rise to a mixture of Ni^o and NiO. The results revealed that the compound undergoes dehydration at 160°C and melts at 310°C. The water thus released hydrolyses surface acetate groups, acetic acid being evolved into the gas phase. At 330°C, the anhydrous acetate is converted into NiCO₃, releasing CH₃COCH₃ into the gas phase. The carbonate subsequently decomposes (at 365°C) to give NiO_(s), CO_2(g) and CO_(g). On further heating up to 373°C, a mixture of Ni^o and NiO is formed. Other gas-phase products were detected at 400°C, viz. CH₄ and (CH₃)₂CH=CH₂, which were formed in surface reactions involving initial gas-phase products. Non-isothermal kinetic parameters (A and ΔE) were calculated on the basis of temperature shifts experienced in the various decomposition processes as a function of heating rate (2–20 deg·min^?1).     

Thermal Decomposition of Ni(II) and Fe(III) Nitrates and their Mixture

The thermal decompositions of nickel(II) nitrate hexahydrate and iron(III) nitrate nonahydrate were followed. It was found that the final decomposition products were NiO at 623 K and Fe2O3 at 523 K, respectively. The two salts exhibited only endothermic peaks and a loss in mass until constant mass was attained. The decomposition reactions and the compounds corresponding to each reaction were established. A heating rate of 1 K min-1 revealed several intermediates; higher heating rates shifted the peaks to higher temperatures. The use of an air flow during decomposition shifted the reactions to lower temperatures. The DTA for the mixed salts was found to be an overlap and the TG a summation of the results for the two individual salts. At 773 K, the decomposition products were composed of three phases: NiO, Fe2O3 and NiFe2O4. When these products were heated to 1773 K, only NiFe2O4 was identified by X-ray diffraction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition of Cd(CH3COO)2·2H2O studied by a coupled TG-DTA-MS method

The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH₃COO)₂·2H₂O is a two-stage process with Cd(CH₃COO)₂·H₂O as intermediate. The way of Cd(CH₃COO)₂ decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO₂ are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions in which intermediates, Cd and CdCO₃, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with oxygen. This revised version was published online in July 2006 with corrections to the Cover Date.     

The thermal decomposition of (NH4)4V2O11 in a nitrogen atmosphere and the kinetics of the first decomposition step

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min^?1 ammonium peroxo vanadate, (NH₄)₄V₂O₁₁, decomposes to (NH₄)[VO (O₂)₂ (NH₃)] (above 93°C); this in turn decomposes to (NH₄) [VO₃ (NH₃)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol^?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol^?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.     

Synthesis of (trichloromethyl)organosilanes by catalytic decarboxylation of (trichloroacetoxy)organosilanes

A method for preparing (trichloromethyl)organosilanes by the catalytic decarboxylation of the corresponding trichloroacetoxysilanes RMe₂SiOC(O)CCl₃ (R = Me, ClCH₂, Ph, Me₃Si, and H) has been developed. The method involves heating the starting compounds without a solvent in the presence of a catalyst (quaternary ammonium salts or potassium salts with the addition of crown ethers). Tertiary amines (Et₃N, Bu₃N) catalyze this reaction only when heating is carried out in donor aprotic solvents (THF, acetonitrile) in the presence of oxygen. Thermal decomposition of (trichloroacetoxy)organosilanes, in contrast to catalytic decarboxylation, begins at a higher temperature and yields a mixture of products.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 150–153, January, 1995.     

Thermal properties of [MII(phen)3]2V4O12·phen·22H2O (M II=Co,Ni, Cu,phen=1,10-phenanthroline)

Thermal decomposition of three tetravanadates, [M^II(phen)₃]₂V₄O₁₂·phen·22H₂O, where M ^II is Co (1), Ni (2), Cu (3) and phen is 1,10-phenanthroline, was studied by dynamic method (for 1 and 2) or isothermally (for 3). The thermal decomposition of the studied compounds is a multi-step process which involve: discontinuous dehydration, release of uncoordinated, and of coordinated phenanthroline molecules. In course of the latter process, a phase transition of the cyclo-tetravanadates to polymeric metavanadates occurred. Metavanadates with chain structure of the anion were the final decomposition products of all tetravanadates studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cycloalkyl-substituted salicylaldimine-nickel(II) complexes as mediators in controlled radical polymerization of vinyl acetate

Abstract

Nickel(II) complexes of Schiff base derived from cycloalkylamines (cycloalkyl?=?cyclopentyl (cpen), cyclohexyl (chex), and cycloheptyl (chep)) were synthesized: [Ni^II(L^cpen)₂] (1), [Ni^II(L^chex)₂] (2), and [Ni^II(L^chep)₂] (3). The Schiff base-Ni^II complexes 1-3 were characterized by FTIR, UV–Vis, elemental analysis, and computational methods. Electrodeposited films of complexes 1–3 were obtained by potential cycling CH₂Cl₂ on platinum electrode, and their electrochemical behavior were characterized by cyclic voltammetry. The polymerization of vinyl acetate (VAc) initiated by azobisisobutyronitrile (AIBN) at 55?°C were conducted according to an organometallic-mediated radical polymerization (OMRP) mechanism. The best conversions were obtained using a ratio of [VAc]/[AIBN]/[Ni]?=?542/3.25/1, reaching 50, 69 and 85% in 12?h for 1, 2 and 3, respectively. The kinetic of polymerization mediated by complex 1 exhibited a linear dependence of ln([VAc]₀/[VAc]) versus time, supporting a constant radical concentration; while for the complexes 2 and 3, the radical concentration was constant for a short period of time. The increase of molecular weights with the conversion coupled with low polydispersities indicate a certain level of control of the polymerization when using the complexes [Ni^II(L^R)₂] as controlling agents.     

Bis‐NHC Chelate Complexes of Nickel(0) and Platinum(0)

For a long time d¹⁰‐ML₂ fragments have been known for their potential to activate unreactive bonds by oxidative addition. In the development of more active species, two approaches have proven successful: the use of strong σ‐donating ligands leading to electron‐rich metal centers and the employment of chelating ligands resulting in a bent coordination geometry. Combining these two strategies, we synthesized bis‐NHC chelate complexes of nickel(0) and platinum(0). Bis(1,5‐cyclooctadiene)nickel(0) and ‐platinum(0) react with bisimidazolium salts, deprotonated in situ at room temperature, to yield tetrahedral or trigonal‐planar bis‐NHC chelate olefin complexes. The synthesis and characterization of these complexes as well as a first example of C? C bond activation with these systems are reported. Due to the enforced cis arrangement of two NHCs, these compounds should open interesting perspectives for bond‐activation chemistry and catalysis.     

DSC kinetics of the thermal decomposition of copper(II) oxalate by isoconversional and maximum rate (peak) methods

The copper(II) oxalate was synthesized, characterized using FT-IR and scanning electron microscopy and its non-isothermal decomposition was studied by differential scanning calorimetric at different heating rates. The kinetics of the thermal decomposition was investigated using different isoconversional and maximum rate (peak) methods viz. Kissinger–Akahira–Sunose (KAS), Tang, Starink^1.95, Starink^1.92, Flynn–Wall–Ozawa (FWO) and Bosewell. The activation energy values obtained from isoconversional methods of FWO and Bosewell are 0.9 and 3.0 %, respectively, higher than that obtained from other methods. The variation of activation energy, E _α with conversion function, α, established using these different methods were found to be similar. Compared to the FWO method, the KAS method offers a significant improvement in the accuracy of the E _a values. All but the Bosewell maximum rate (peak) methods yielded consistent values of E _α (~137 kJ mol^?1); however, the complexity of the thermal decomposition reaction can be identified only through isoconversional methods.     

Thermal decomposition kinetics. Part XI. Mechanism of thermal decomposition of calcium oxalate monohydrate from a thermogravimetric study — the effects of heating rate and sample mass on kinetic parameters from mechanistic equations

The mechanisms of the first two stages of the thermal decomposition of calcium oxalate monohydrate

have been established from non-isothermal thermogravimetric studies. For both stages, the rate-controlling processes are phase boundary reactions; the dehydration step assumes spherical symmetry whereas the decomposition step follows cylindrical symmetry. The kinetic parameters calculated from mechanistic equations show the same trend as those from mechanism-non-invoking equations. Thus, for the decomposition of CaC₂O₄ the kinetic parameters are not appreciably affected by heating rate or sample mass. For the dehydration step they show a systematic decrease with increase in either heating rate or sample mass. The best fit correlations can be expressed as follows E(or, log A) = (Constant/Heating rate) + Constant, (at fixed sample mass) E(or, log A) = (Constant) × (Mass)² ? (Constant) × (Mass) + Constant, (at fixed heating rate)     

Influence of sample particle size and heating rate on the thermal decomposition of K2C2O4

The thermal decomposition of K₂C₂O₄ in a current of dry nitrogen according to the reaction (1) $$K_2 C_2 O_4 \to K_2 CO_3 + CO$$ is shown to be influenced profoundly by the sample particle size and the heating rate. For finely ground samples, a lower activation energy (E _a =255.15±5 kJ mol^?1) is obtained as compared with the 312.6±6 kJ mol^?1 observed for crystal chips weighing 30–40 mg. The characteristic temperatures (the reaction start, peak and end temperatures) are markedly reduced by fine grinding. High heating rates tend to separate the thermal decomposition process into two kinetic phases, shown by splitting of the DTG peak. The significance of these observations is discussed, and the results are theoretically accounted for.     

Thermal deamination kinetics of tris(ethylenediamine)nickel(II) sulphate in the solid-state

Thermogravimetric techniques have been used to study the kinetics of thermal deamination of tris(ethylenediamine)nickel(II) sulphate. The complex was synthesized and characterized by various chemical and spectral techniques. Thermal decomposition studies were carried at different heating rates (5, 10, 15 and 20°C min⁻¹) in dynamic air. The complex undergoes a four-stage decomposition pattern. The stages are not well resolved. Decomposition path can be interpreted as a two-stage deamination, and a two-stage decomposition. Reaction products at each stage were separated and identified by means of IR and XRD. The morphology of the complex and the residue were studied by means of SEM. Final residue of the decomposition was found to be crystalline NiO. The deamination kinetics was studied using model-free isoconversional methods viz., Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. It is observed that the activation energy varies with the extent of conversion; indicating the complex nature of the deamination reaction.     

Homoleptic Organoderivatives of High‐Valent Nickel(III)

Homoleptic perhalophenyl derivatives of divalent nickel complexes with the general formula [NBu₄]₂[Ni^II (C₆X₅)₄] [X=F ( 1 ), Cl ( 2 )] have been prepared by low‐temperature treatment of the halo‐complex precursor [NBu₄]₂[NiBr₄] with the corresponding organolithium reagent LiC₆X₅. Compounds 1 and 2 are electrochemically related by reversible one‐electron exchange processes with the corresponding organometallate(III) compounds [NBu₄][Ni^III (C₆X₅)₄] [X=F ( 3 ), Cl ( 4 )]. The potentials of the [Ni^III (C₆X₅)₄]^?/[Ni^II (C₆X₅)₄]^2? couples are +0.07 and ?0.11 V for X=F or Cl, respectively. Compounds 3 and 4 have also been prepared and isolated in good yield by chemical oxidation of 1 or 2 with bromine or the amminium salt [N(C₆H₄Br‐4)₃][SbCl₆]. The [Ni^III (C₆X₅)₄]^? species have SP‐4 structures in the salts 3 and 4 , as established by single‐crystal X‐ray diffraction methods. The [Ni^II (C₆F₅)₄]^2? ion in the parent compound 1 has also been found to exhibit a rather similar SP‐4 structure. According to their SP‐4 geometry, the Ni^III compounds (d⁷) behave as S=1/2 systems both at microscopic (EPR) and macroscopic levels (ac and dc magnetization measurements). The spin Hamiltonian parameters obtained from the analysis of the magnetic behavior of 3 and 4 within the framework of ligand field theory show that the unpaired electron is centered mainly on the metal atom, with >97 % estimated d contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C₆X₅? C₆X₅ coupling compounds.     

Solid—liquid phase diagrams of mixtures containing substituted phenols and amine mixtures

The thermal decomposition of CaCO₃ was studied under high vacuum by means of both TG and the more recently developed constant decomposition rate thermal analysis (CRTA) which allows the monitoring of both reaction rate and the residual pressure over the sample. The reliability of the kinetic results seems to be much higher with the latter technique which actually allows the reduction of the reaction rate and therefore the heat and mass transfer effects over a broad range of sample size. For instance, it was necessary, by conventional TG started under a vacuum of 2 10^?6 torr with a heating rate of 0.5 K min^?1, to lower the amount of sample to 2 mg in order to obtain the same activation energy as that calculated from CRTA with various samples weighing up to 50 mg. The TG experimental conditions quoted above (and which are upper limits of mass and heating rate) are beyond the limit of sensitivity of most available conventional TG equipment.     

Insoluble Fe(VI) compounds: effects on the super-iron battery

Cathodes composed of Fe(VI) salts are capable of three-electron reduction, and are useful for energetic super-iron batteries. This study investigates the solubility of BaFeO₄ and K₂FeO₄ Fe(VI) salts. Electrolytes are determined in which Fe(VI) has a low aqueous or non-aqueous solubility, or is insoluble. Insoluble Fe(VI) salts have the duel benefits of preventing Fe(VI) solution-phase (i) decomposition and (ii) diffusion to the anode; thereby preventing super-iron battery self-discharge. BaFeO₄ is insoluble in water, and has a solubility of less than 2×10⁻⁴ M in 5 M KOH containing Ba(OH)₂. A BaFeO₄ super-iron battery has a high discharge efficiency when containing an electrolyte of either 12 M KOH, or 6 M KOH saturated in Ba(OH)₂. Fe(VI) cathodes in non-aqueous media may be useful in providing a high-capacity Li or Li-ion super-iron battery. We illustrate that Fe(VI) salts are insoluble and chemically unreactive with a range of organic electrolytes, and can be discharged as cathodes in non-aqueous electrolytes. In acetonitrile containing 1 M LiClO₄, the discharge of an Fe(VI) cathode is demonstrated to a capacity over 394 mAh g⁻¹ K₂FeO₄.     

Hydrogen Bonds as Structural Directive towards Unusual Polynuclear Complexes: Synthesis,Structure, and Magnetic Properties of Copper(II) and Nickel(II) Complexes with a 2-Aminoglucose Ligand

The reaction of benzyl 2-amino-4,6-O-benzylidene-2-deoxy-α-D -glucopyranoside (HL) with the metal salts Cu(ClO₄)₂ ⋅ 6 H₂O and Ni(NO₃)₂ ⋅ 6 H₂O affords via self-assembly a tetranuclear μ₄-hydroxido bridged copper(II) complex [(μ₄-OH)Cu₄(L)₄(MeOH)₃(H₂O)](ClO₄)₃ ( 1 ) and a trinuclear alcoholate bridged nickel(II) complex [Ni₃(L)₅(HL)]NO₃ ( 2 ), respectively. Both complexes crystallize in the acentric space group P2₁. The X-ray crystal structure reveals the rare (μ₄-OH)Cu₄O₄ core for complex 1 which is μ₂-alcoholate bridged. The copper(II) ions possess a distorted square-pyramidal geometry with an [NO₄] donor set. The core is stabilized by hydrogen bonding between the coordinating amino group of the glucose backbone and the benzylidene protected oxygen atom O4 of a neighboring {Cu(L)} fragment as hydrogen-bond acceptor. For complex 2 an [N₄O₂] donor set is observed at the nickel(II) ions with a distorted octahedral geometry. The trinuclear isosceles Ni₃ core is bridged by μ₃-alcoholate O3 oxygen atoms of two glucose ligands. The two short edges are capped by μ₂-alcoholate O3 oxygen atoms of the two ligands coordinated at the nickel(II) ion at the vertex of these two edges. Along the elongated edge of the triangle a strong hydrogen bond (244 pm) between the O3 oxygen atoms of ligands coordinating at the two relevant nickel(II) ions is observed. The coordinating amino groups of the these two glucose ligands are involved in additional hydrogen bonds with O4 oxygen atoms of adjacent ligands further stabilizing the trinuclear core. The carbohydrate backbones in all cases adopt the stable ⁴C₁ chair conformation and exhibit the rare chitosan-like trans-2,3-chelation. Temperature dependent magnetic measurements indicate an overall antiferromagnetic behavior for complex 1 with J₁=−260 and J₂=−205 cm⁻¹ (g=2.122). Compound 2 is the first ferromagnetically coupled trinuclear nickel(II) complex with J_A=16.4 and J_B=11.0 cm⁻¹ (g_1,2=2.183, g₃=2.247). For the high-spin nickel(II) centers a zero-field splitting of D_1,2=3.7 cm⁻¹ and D₃=1.8 cm⁻¹ is observed. The S=3 ground state of complex 2 is consistent with magnetization measurements at low temperatures.     

Irreversible Structural Phase Transition in [(9-triptycylammonium) ([18]crown-6)][Ni(dmit)2]: Origin and Effects on Electrical and Magnetic Properties

Materials exhibiting irreversible phase transitions, leading to changes in their properties, have a potential for novel application in electronic components such as a non-rewritable high-security memory. Here, we focused on the two salts, [(9-triptycylammonium)([18]crown-6)][Ni(dmit)₂] ( 1 ) and [(9-triptycylammonium)([15]crown-5)][Ni(dmit)₂] ( 2 ), which featured 2D sheet structures with alternately stacked cation and anion layers. Both salts exhibit similar cation arrangements, however, their anion arrangements differ significantly. The temperature-dependent magnetic susceptibilities of 1 and 2 were well reproduced by the alternating chain model (J_AC1/k_B=−306(8), J_AC2/k_B=−239(3) K) and the Curie-Weiss model (θ=−3.9(1) K), respectively. 1 experience a reversible phase transition around 40–60 K, causing anomalies in magnetic behavior. Moreover, an irreversible single-crystal-to-single-crystal phase transition to 1′ undergo at ~381 K, inducing a rearrangement of [Ni(dmit)₂]⁻ anions and a resistivity decrease from 6.5×10⁶ to 6.5×10² Ω cm. The susceptibility curve of 1′ was reproduced by a combination of the Curie-Weiss and dimer models (J_dimer/k_B=−407(5), θ=−26.7(5) K). The irreversible transition of 1 is the first example for such supramolecule and [Ni(dmit)₂]⁻ system to our knowledge, in opening potential new-type materials.     

Principal component analysis of thermal decomposition of magnesium salts used as drugs

Thermal decomposition of magnesium salts of organic acids used in medicine (Mg acetate, Mg valproate, Mg lactate, Mg citrate, Mg hydrogen aspartate, Zn hydrogen aspartate) was analyzed by thermoanalytical, calorimetrical, and computational methods. Thermoanalytical studies were performed with aid of a derivatograph. 50-, 100-, and 200-mg samples were heated in a static air atmosphere at a heating rate of 3, 5, 10, and 15 °C min⁻¹ up to the final temperature of 700–900 °C. By differential thermal analysis (DTA), thermogravimetry (TG), and derivative thermogravimetry (DTG) methods, it has been established that thermal decomposition of the salts under study occurs via two stages. The first stage (dehydratation) was distinctly marked on the thermoanalytical curves. Calorimetrical studies were carried out by using of a heat-flux Mettler Toledo differential scanning calorimetry (DSC) system. Ten milligram samples of compounds under study were heated in the temperature range from 20 to 400 °C at a heating rate of 10 and 20 °C min⁻¹ under an air stream. The studies showed that the values of transitions heats and enthalpies of dehydration for investigated salts varied with the increasing of heating rate. For chemometric evaluation of thermoanalytical results, the principal component analysis (PCA) was applied. This method revealed that points on PC1 versus PC2 diagrams corresponding to the compounds of similar chemical constitution are localized in the similar ranges of the first two PC’s values. This proves that thermal decomposition reflects similarity in the structure of magnesium salts of organic acids.     

Investigation of Bis(Perfluoro-tert-Butoxy) Halogenates(I/III)

A systematic study of halogenate(I/III) anions with polyatomic ligands is presented. The bis(perfluoro-tert-butoxy) halogenates(I) [X(OC₄F₉)₂]⁻, X=Cl, Br, I, of chlorine, bromine, and iodine are prepared as their tetraethylammonium salts and characterized with IR, Raman, and NMR spectroscopic methods, as well as single-crystal X-ray diffraction analyses. Spectroscopical data are supported by quantum-chemical calculations. Additionally, the bonding situation of the species in question are analyzed and discussed. Furthermore, the oxidation to the corresponding halogenate(III) derivatives was studied. For [Br(OC₄F₉)₂]⁻, oxidation with elemental fluorine gave [BrF₂(OC₄F₉)₂]⁻. Iodide was directly oxidized by ClOC₄F₉ to the I^III species [I(OC₄F₉)₄]⁻, which is a surprisingly inert anion that might be used as a weakly coordinating anion (WCA) in the future. For [Cl(OC₄F₉)₂]⁻, the decomposition products of the synthetic approaches towards a chlorine(III) system were analyzed.     

New POCOP-type pincer complexes of Nickel(II)

The pincer complex [(POCOP)Ni(NCMe)][OSO₂CF₃] (1: POCOP = {2,6-(i-Pr₂PO)₂C₆H₃}) undergoes an acetonitrile substitution reaction in the presence of CN(t-Bu), KCN, and KOCN to give the new complexes [(POCOP)Ni{CN(t-Bu)}][O₃SCF₃] and (POCOP)Ni(X) (X = CN and NCO). The Ni-CN derivative is also obtained from a gradual decomposition of the Ni-CN(t-Bu) derivative, while the aquo derivative [(POCOP)Ni(OH₂)][O₃SCF₃] was obtained from slow hydrolysis of (POCOP)Ni(OSO₂CF₃). All new complexes have been characterized spectroscopically and by X-ray crystallography. IR and solid state structural data indicate that Ni-L/X interactions are dominated by ligand-to-metal σ-donation; presence of little or no π-backbonding is consistent with the electrophilicity of the cationic fragment [(POCOP)Ni]⁺.