Conductometric and DSC evidence for a high temperature phase transition in cobalt dibromide

A solid-state phase transition in cobalt dibromide at 647 K has been revealed by three different alternative current techniques. A small thermal effect of (181±18) J mol⁻¹ corresponding to the enthalpy of the transition has been determined by differential scanning calorimetry. The effect was observed on cooling and on heating as well.     

The solid state reactions of o-aminobenzoic acid with Zn(Ⅱ), Cu(Ⅱ), Ni(Ⅱ), Mn(Ⅱ) acetate hydrate at room temperature

The solid-solid state reactions of o-aminobenzoic acid with Zn(OAc)2.2H2O, Cu(OAc)2 .H2O, Ni(OAc)2.4H2O and Mn(OAc)2.4H2O result in the formation of corresponding complexes M(OAB)2 (M = Zn(Ⅱ), Cu(Ⅱ), Ni(Ⅱ), Mn(IⅡ)). XRD, IR and elemental analysis methods have been used to characterize the solid products. The activation energies of these reactions, which are calculated from the kinetic data obtained by means of the isothermal electrical conductivity measurement method, have been found to increase in the order: Cu(OAc)2.H2O(37.7 kJ.mol-1)~Mn(OAc)2.4H2O (39.7kJ.mol-1) < Zn(OAc)2.2H2O (56.3 kJ.mol-1) < Ni(OAc)2.4H2O (85.2 kJ.mol-1). The trend is related to their crystal structures.     

Structural characterization of polypyrrole in the solid state by high resolution 15N NMR spectroscopy [II]

The solid-state ¹⁵N CP/MAS NMR spectra and ¹⁵N spin-lattice relaxation times (T₁) of doped and dedoped ¹⁵N-labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high-resolution solid-state ¹⁵N NMR. The ¹⁵N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half-width of the ¹⁵N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wiley & Sons, Inc.     

Studies on solid state synthesis and the oxygenation property of cobalt (II) Schiff base (vanilline polyamine) complexes

Three new cobalt complexes were synthesized by solid-state reaction at room temperature and the resultant Co complexes reacted with two equivalent oxygen molecules at room temperature to produce the oxygenated complexes [Co·(L₁)₂·(O₂)₂](NO₃)₂·2H₂O (L₁ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl)-diethylenetriamine), [Co·(L₂)₂·(O₂)₂](NO₃)₂·2H₂O (L₂ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl)-triethylenetetramine), and [Co·(L₃)₂·(O₂)₂](NO₃)₂·2H₂O (L₃ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl-tetraethylenepentamine). The oxygenated complexes were characterized by elemental analysis, IR (Infrared), ¹H-NMR (Nuclear Magnetic Resonance), and UV-Vis (Ultraviolet Visual) spectrometry, and TG/DTA (Thermogravimetry/Differential Thermal Analysis) analysis, and molar conductance. The coordinated oxygen contents in the oxygenated complexes were also determined by weight method. It was supposed that only one O₂ molecule coordinated to the Co ion forming a superoxo type oxygenated complex. Translated from Acta Chimica Sinica, 2006, 64(15): 1517–1522 (in Chinese)     

The solid state and solution chemistry of dichlorobis(pyridine)cobalt(II)

The thermal decomposition of dichlorobisquinolinecobalt(II) was investigated. Kinetic analyses were performed on the dynamic and isothermal curves. The dynamic and d.s.c. studies revealed two simultaneously reactions while the isothermal reactions represented single processes. The scheme of thermal decomposition is:

Electrical conductivity in solid solutions and in two-phase regions of the silver halide-bivalent metal (cadmium,cobalt, zinc) halide systems

Electrical conductivity of solid systems AgX-MX₂ (where M=Cd, Co, Zn and X=Cl, Br) were measured in a large range of temperature and compositions. Activation energies and conductivity values vs. composition are presented and discussed in relation to phase equilibria in the respective systems. Maximum of the conductivity value and stabilization of the activation energy have been found for silver halides doped heavily with divalent cation e.g. in the systems forming solid solutions on the silver halide side. Disorder in AgBr on the approach to melting, expected to be higher than in AgCl, has been shown by means of original DSC curves presented for both halides.     

Synthesis,characterization, corrosion inhibition of mild steel in HCl (0.5 N) solution and solid‐state electrical conductivity of new Co(II), Ni(II), Cu(II) and Zn(II) complexes

This work consists of a study of the corrosion‐inhibiting and semiconducting properties of new binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes with a Schiff base, H₂L, obtained from the 2:1 M condensation of salicylaldehyde and o‐dianisidine, respectively. Elemental, spectral and thermal analyses were used to characterize these complexes. The magnetic susceptibilities of these complexes were also determined. Weight loss, potentiodynamic polarization and scanning optical microscopy were the techniques used to investigate the efficiency of these new compounds as corrosion inhibitors. The antibacterial activity of the compounds was measured against sulfate‐reducing bacteria. It was found that inhibition occurs via the chemisorption of metal complexes on the steel surface. This absorption obeys the Langmuir adsorption isotherm model.     

Crystal structure, spectroscopy and magnetism of trinuclear nickel(II), cobalt(II) complexes and their solid solution

Four new complexes [Ni₃(μ-L)₆(H₂O)₆](NO₃)₆·6H₂O (1), [Co₃(μ-L)₆(H₂O)₆](NO₃)₆·6H₂O (2), [Ni₃(μ-L)₆(H₂O)₄(CH₃OH)₂](NO₃)₆·4H₂O (3), [Co₃(μ-L)₆(H₂O)₄(CH₃OH)₂](NO₃)₆·4H₂O (4) (L = 4-amino-3,5-dimethanyl-1,2,4-triazole) were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complex 1 and 2 are isomorphous; complex 3 and 4 are isomorphous. Four complexes all consist of the linear trinuclear cations ([M₃(μ-L)₆(H₂O)₆]⁶⁺ (M = Ni,Co) for 1 and 2; [M₃(μ-L)₆(H₂O)₄(CH₃OH)₂]⁶⁺ (M = Ni,Co) for 3 and 4), NO₃⁻ anions and crystallized water molecules. In the trinuclear cations, the central M(II) ions and two terminal M(II) ions are bridged by three triazole ligands. Other eleven solid solution compounds which are isomorphous with complex 3 and 4 were obtained by using different ratio of Ni(II) and Co(II) ions as reactants and ICP result indicates that ligand L has higher selectivity of Ni(II) ions than that of Co(II) ions. The magnetic analysis was carried out by using the isotropic spin Hamiltonian ? = −2J(?₁?₂ + ?₂?₃) (for complexes 1 and 3) and simultaneously considering the temperature dependent g factor (for complexes 2 and 4). Both the UV-Vis spectra and the magnetic properties of the solid solutions can be altered systematically by adjusting the Co(II)/Ni(II) ratio.     

Solid-phase thermal decomposition of polynuclear nickel(II) and cobalt(II) complexes

Solid-phase thermal decomposition of polynuclear Ni^II and Co^II pivalate complexes was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the polynuclear (from bi-to hexanuclear) Co^II carboxylate complexes is accompanied by aggregation to form a volatile octanuclear complex. Thermolysis of the polynuclear NiII carboxylates results in their destructure, and the phase composition of the decomposition products is determined by the nature of coordinated ligands. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 250—260, February, 2006.     

Structure and phase transitions in guanidinium halogenobismuthates(III)

Differential scanning calorimetry (DSC), dilatometric and dielectric measurements have been used to study the phase transitions in [C(NH₂)₃]₃BiBr₆. The [C(NH₂)₃]₃BiBr₆ crystal undergoes four phase transitions: at 419, 429, 475 and 495 K (on heating). The high-temperature phase transition is clearly of first-order type and its high entropy effect allows classifying it as of the order–disorder type. X-ray diffraction studies showed that [C(NH₂)₃]₃BiBr₆ crystallises in monoclinic, centrosymmetric space group, C2/c. The anionic sublattice is composed of isolated BiBr₆³⁻ octahedra. The infrared between 100 and 350 K and Raman spectra at room temperature in the frequency range related to the internal vibrations of guanidinium cations were studied for [C(NH₂)₃]₃BiBr₆, [C(NH₂)₃]₃Bi₂Br₉, [C(NH₂)₃]₃BiCl₆xCl₂ and C(NH₂)₃Cl to analyse the dynamical state of cations. At room temperature, the cations in the studied guanidinium halogenobismuthates(III) are almost rigid, so the mechanism of high-temperature phase transitions is probably connected with the release of rotation of the cations.     

Conformational polymorphism in a cobalt(II) dithiocarbamate complex

Two conformational polymorphs of (N,N‐dibutyldithiocarbamato‐κ²S,S′)[tris(3,5‐diphenylpyrazol‐1‐yl‐κN²)hydroborato]cobalt(II), [Co(C₄₅H₃₄BN₆)(C₉H₁₈NS₂)] or [Tp^Ph2Co(S₂CNBu₂)], 1 , are accessible by recrystallization from dichloromethane–methanol to give orthorhombic polymorph 1a , while slow evaporation from acetonitrile produces triclinic polymorph 1b . The two polymorphs have been characterized by IR spectroscopy and single‐crystal X‐ray crystallography at 150 K. Polymorphs 1a and 1b crystallize in the orthorhombic space group Pbca and the triclinic space group P, respectively. The polymorphs have a trans ( 1a ) and cis ( 1b ) orientation of the butyl groups with respect to the S₂CN plane of the dithiocarbamate ligand, which results in an intermediate five‐coordinate geometry for 1a and a square‐pyramidal geometry for 1b . Hirshfeld surface analysis reveals minor differences between the two polymorphs, with 1a exhibiting stronger C—H…S interactions and 1b favouring C—H…π interactions.     

Melting and glass transitions in paraffinic and naphthenic oils

Naphthenic and paraffinic oils were analyzed by modulated differential scanning calorimetry (MDSC). The results showed several improvements in the analysis of thermal properties when compared with standard DSC. The glass transition temperature (T_g), the enthalpy relaxation at T_g, and the melting endotherms could be deconvoluted, and reversible melting could be identified. This allowed for an easier interpretation of the thermal properties of the oils. With MDSC, the T_gs in mineral oils were found to coincide with endothermic enthalpy relaxation, which is generally regarded as a melting endotherm with standard DSC. A decrease in heat capacity after T_g was attributed to the existence of rigid amorphous material. From Δc_p at T_g and the oil molecular weight, the number of repeat units in the oil chains was estimated at less than 20. The T_g of a hypothetical pure aromatic oil was found to be similar to that for petroleum asphaltenes, and that for a naphthenic oil of infinite molecular weight to be similar to that of petroleum resins.     

Synthesis and crystal structure of polymer cobalt(II) complex, 1,2,4,5-benzenetetracarboxylate hexaimidazole tetraaqua cobalt (II) tetrahydrate

The crystal structure of the title complex {[Co(TCB)2/2-(IMI)2(H2O)2][Co(IMI)4(H2O)2] } (H2O)4 (where TCB = 1,2,4,5-benzenetetracarboxylic anion; IMI = imidazole) has been determined by X-ray diffraction method. Crystal data for {[Co(TCB)2/2(IMI)2(H2O)2][Co(IMI)4(H2O)2]}-(H2O)4: triclinic, space group P 1, a = 1.0647(2) nm, b = 1.1165(1)nm,c = 1.00361(1)nm,α = 91.56(1)°,β = 111.34(1)°, γ = 115.642(10)°, V = 0.9772(3) nm5, Z = 1. The polymer cobalt (II) complex has a novel three-dimension network structure. Co(1) atom and Co(2) atom both are coordinated in an octahedral arrangement and located in the center of the coordination anion and the center of the coordination cation, respectively. Moreover four carboxyl groups of TCB are divided into two types, two para-carboxyl groups bridge Co(1) atom in monodentate fashion and other two para-carboxyl groups are in free.     

Mild template synthesis in the CoII-dithiooxamide-glyoxal system in cobalt(II) hexacyanoferrate(II) gelatin-immobilized matrices

Complexation processes in a cobalt(II) hexacyanoferrate(II) gelatin-immobilized matrix under the action of aqueous solutions containing dithiooxamide H₂N−C(S)−C(S)−NH₂ and glyoxal HOC−CHO at pH>10 were studied. Under these conditions, mild template synthesis occurs to form a Co^III chelate with the (N,N,S,S)-ligand,viz. 2,7-dithio-3,6-diazaoctadiene-3,5-dithioamide-1,8, with a metal to ligand ratio of 1∶1, where dithiooxamide and glyoxal act as ligand synthons. The reaction mechanism is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1999–2004, October, 1999.     

Temperature modulated differential scanning calorimetry (TMDSC) in the region of phase transitions. Part 1: theoretical considerations

For temperature modulated differential scanning calorimetry (TMDSC) a simple model, the low pass filter, is presented which allows to see and calculate the influence of heat transfer into the sample on magnitude and phase shift of the modulated part of the measured heat flow rate and the heat capacity determined from it. A formula is given which enables to correct the measured magnitude of the periodic heat flow rate function and the calculated heat capacity in dependence on the thermal resistance and heat capacity of the sample. The correction becomes very important in regions where the heat capacity changes considerably as in the melting region. The approach is successfully tested with model substances with well-known excess heat capacity in the transition region.     

Gaseous complexes of cobalt(II) bromide and pyridine

The stepwise decomposition of CoBr₂py₂(s) has been investigated on a thermobalance by the “modified entrainment” method yielding Δ₁H=88.6 kJ mol¹, Δ₁S=156.6 JK^?1 mol^?1 and Δ₂H=119.0 kJ mol^?1, Δ₂S=211.8 JK^?1 mol^?1 for the dissociation of the first and second pyridine. The evaporation of CoBr₂py₂(l) and the association of gaseous pyridine to CoBr₂py(l) forming CoBr₂py₂(g) has been studied by vis spectroscopy at 250?420°C. By combining the new results with literature values, a complete thermodynamic cycle for the solid-liquid-gas equilibria in the CoBr₂-pyridine system could be established. It shows that in solution the formation of CoBr₂py₂ is not determined by the cobalt-pyridine bond energy but by the solvation energy of the rectants.     

PVC matrix membrane electrodes based on cobalt and nickel phenanthroline complexes for selective determination of cobalt(II) and nickel(II) ions

Potentiometric sensors for determining cobalt and nickel ions are described. They are based on the use of cobalt and nickel tris(1,10-phenanthroline)-TPB as electroactive compounds dispersed in plasticized poly(vinyl chloride) matrix. The sensors exhibit fast, near-Nernstian responses for cobalt and nickel-phenanthroline cations over the pH range 3–11 with a slope of 30.3 ± 0.3 mV/concentration decade. In the presence of excess 1,10-phenanthroline reagent, cobalt(II) and nickel(II) ions at concentration levels as low as 4 × 10^–6 M are accurately determined. The results show an average metal ion recovery of 98.5% with a mean standard deviation of 0.5%. Cobalt in organometallic compounds and nickel in silicate rocks are determined by these sensors and results agreeing fairly well with atomic absorption spectrometry are obtained.     

Cobalt(II) and cobalt(III) dipicolinate complexes: solid state,solution, and in vivo insulin-like properties

The synthesis and characterization of Co(II) and Co(III) 2,6-pyridinedicarboxylate (dipic(2-)) complexes are reported. Solid-state X-ray characterizations were performed on [Co(H(2)dipic)(dipic)].3H(2)O and [Co(dipic)(mu-dipic)Co(H(2)O)(5)].2H(2)O. Two coordination modes not previously observed in dipicolinate transition metal complexes were observed in these complexes; one involves metal coordination to the short C-O (C=O) bond, and the other involves metal coordination to a protonated oxygen atom. Solution studies, including paramagnetic NMR and UV-vis spectroscopy, were done showing the high stability and low lability of the Co(III) complex, whereas the Co(II) complexes exhibited ligand exchange in the presence of excess ligand. The [Co(dipic)(2)](2-) complex has pH dependent lability and in this regard is most similar to the [VO(2)dipic](-) complex. The [Co(dipic)(2)](2-) was found to be effective in reducing the hyperlipidemia of diabetes using oral administration in drinking water in rats with STZ-induced diabetes. Oral administration of VOSO(4) was used as a positive control for metal efficacy against diabetes. In addition to providing a framework to evaluate structure-function relationships of various transition metal complexes in alleviating the symptoms of diabetes, this work describes novel aspects of structural and solution cobalt chemistry.