Search

A new compound, [Co(H2O)6](ClO4)2.(HMTA)2.2H2O; HMTA = hexamethylenetetramine) has been synthesized and characterized with the assistance of X-ray crystallography, elemental analysis, FT-IR spectroscopy, TG-DTA and DSC (N2 atmosphere). Both TG data model-fitting method as well as method of model free isoconversional have been employed to observe the kinetics of thermolysis of the compound. In order to understand the effect of sudden high heat, measurements of explosion delay are undertaken at regular five unique temperatures and the kinetics of explosion has also been explored using Arrhenius equation. [ABSTRACT FROM AUTHOR]

Searching for new metal–organic frameworks with excellent electrochemical performances is considerably important to advance their application in supercapacitors. Herein, a Co5-cluster-based three-dimensional (3D) metal–organic framework (Co5(OH)2(O2CCH3)8·2H2O, Co5-MOF) was synthesized and characterized by X-ray powder diffraction, infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and nitrogen adsorption–desorption. The Co5-MOF as an electrode material of supercapacitors was investigated for the first time. In a three-electrode system, the highest specific capacitance for the Co5-MOF electrode is 867 F g−1 at 1 A g−1, and the specific capacitance still remains 90.3% of the original specific capacitance after 3000 cycles, displaying its good long-term cycle stability. The asymmetric supercapacitor based on the Co5-MOF as the positive electrode and the rGO as the negative electrode presented a high energy density of 18 W h kg−1 at a power density of 0.7 kW kg−1. The high supercapacitive properties may be attributed to the nano-sized Co5-MOF particles with larger specific surface area and pore structure. [ABSTRACT FROM AUTHOR]

Two CoII‐based coordination polymers, namely poly[(μ4‐biphenyl‐2,2′,5,5′‐tetracarboxylato){μ2‐1,3‐bis[(1H‐imidazol‐1‐yl)methyl]benzene}dicobalt(II)], [Co2(C16H6O8)(C14H14N4)2]n or [Co2(o,m‐bpta)(1,3‐bimb)2]n (I), and poly[[aqua(μ4‐biphenyl‐2,2′,5,5′‐tetracarboxylato){1,4‐bis[(1H‐imidazol‐1‐yl)methyl]benzene}dicobalt(II)] dihydrate], {[Co2(C16H6O8)(C14H14N4)2(H2O)2]·4H2O}n or {[Co2(o,m‐bpta)(1,4‐bimb)2(H2O)2]·4H2O}n (II), were synthesized from a mixture of biphenyl‐2,2′,5,5′‐tetracarboxylic acid, i.e. [H4(o,m‐bpta)], CoCl2·6H2O and N‐donor ligands under solvothermal conditions. The complexes were characterized by IR spectroscopy, elemental analysis, single‐crystal X‐ray diffraction and powder X‐ray diffraction analysis. The bridging (o,m‐bpta)4− ligands combine with CoII ions in different μ4‐coordination modes, leading to the formation of one‐dimensional chains. The central CoII atoms display tetrahedral [CoN2O2] and octahedral [CoN2O4] geometries in I and II, respectively. The bis[(1H‐imidazol‐1‐yl)methyl]benzene (bimb) ligands adopt trans or cis conformations to connect CoII ions, thus forming two three‐dimensional (3D) networks. Complex I shows a (2,4)‐connected 3D network with left‐ and right‐handed helical chains constructed by (o,m‐bpta)4− ligands. Complex II is a (4,4)‐connected 3D novel network with ribbon‐like chains formed by (o,m‐bpta)4− linkers. Magnetic studies indicate an orbital contribution to the magnetic moment of I and II due to the longer Co...Co distances. An attempt has been made to fit the χMT results to the magnetic formulae for mononuclear CoII complexes, the fitting indicating the presence of weak antiferromagnetic interactions between the CoII ions. [ABSTRACT FROM AUTHOR]

At the first co-precipitation stage, with urea as precipitator, the nanosheet was formed by self-assembly due to the synergistic effect between surfactant (sodium dodecyl sulfate, SDS) and inorganic cobalt salt. During the following hydrothermal process, the nanosheet gradually curled into nanotube, which was cobalt compound nanotube with porous and multilayered structure. [Display omitted] • A two-step way for preparing one-dimensional cobalt compound nanotubes was successfully exploited. • The synthesis conditions for the cobalt compound nanotubes were thoroughly investigated. • The formation process of cobalt compound nanotube involves the self-assembly of nanosheets and sheets curling into nanotubes. • The cobalt compound nanotubes with porous and multilayered structure show great pseudo capacitance performance in CV test. Under the synergistic effect between surfactant (sodium dodecyl sulfate, SDS) and inorganic cobalt salt, the ultra-thin nanosheets were firstly formed by self-assembly with urea as precipitant. In the following hydrothermal treatment, these sheets gradually curled into tubes, and finally the cobalt compound nanotube with porous and multilayered structure was obtained. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier infrared transform spectroscopy (FT-IR), N 2 sorption and thermogravimetric analysis (TGA) were employed to characterize the samples, and the results showed that the cobalt compound with layered and tubular nanostructure could be obtained by adjusting the SDS concentration, solvent, hydrothermal time and temperature. The cobalt compound nanotube with multilayered and porous structure has high specific surface area, which provides great high efficiency for electron-transfer and results in high pseudo capacitance in cyclic voltammetry tests. [ABSTRACT FROM AUTHOR]

A new coordination compound using 2,6-pyridinedicarboxylic acid and cobalt(II) ( 1 = {(C 5 H 5 NH)[Co(C 7 H 4 NO 4 )(C 7 H 3 NO 4 )]·(C 7 H 5 NO 4 )·(H 2 O)} n ) was synthesized by slow evaporation. The compound forms a 1D supramolecular structure by alternating metal–organic coordination chains held together by a combination of covalent and non-covalent bonds. The structure was characterized by single crystal X-ray diffraction, FTIR, TGA and DSC. The electrocatalytic properties of 1 were investigated in the oxidation of l -cysteine and it was found to be an able catalyst. [ABSTRACT FROM AUTHOR]

The magnetic and structural parameters of the well-characterized cobalt(II) compound Co 3 (OH) 2 (C 4 O 4 ) 2 ·3H 2 O ( 2 , 3 ) change significantly when the compound is mechanically ground. These parameters are also dependent on the storage conditions of the polycrystalline material before grinding. When the material is stored in an anhydrous (desiccators) environment ( 2 ), the structural properties of the ground sample ( 4 ) agree with the polycrystalline material although the magnetic properties differ somewhat. When storing the material under ambient conditions ( 3 ), the material undergoes a structural transformation after grinding ( 5 ) that is accompanied by changes in magnetic properties. The synthetic precursor ( 1 ) to 2 and 3 also shows magnetic properties that are not observed in 2 , 3 . The powder XRD of 1 suggests that the dominant species in the mixture is Co(C 4 O 4 )(H 2 O) 2 , which provides a new synthetic pathway for 2 and 3 . The synthesis of 1 was performed unprotected from the atmosphere, and therefore the room temperature effective magnetic moment of 1 was well below the other materials studied. The room temperature effective magnetic moment of 1 , 4 , and 5 (per cobalt center) are 4.0, 5.1, and 5.0 μ B . Dynamic magnetic susceptibility of 1 , 4 , and 5 confirm that 1 and the ground derivatives 4 and 5 are not isostructural with the polycrystalline materials. The dynamic susceptibility of 1 is too complex to analyze quantitatively. It contains two peaks and two shoulders that are within 11 K of one another, and a peak at 14 K dominates the rest of the features. 4 and 5 have features that can be analyzed and compared with 2 , 3 . The frequency independent out-of-phase peak associated with 2 , 3 becomes frequency dependent in 4 . The Arrhenius fit to the frequency dependence suggests spin-glass behavior based on the small pre-exponential time of 9.59 × 10 12 s and the physically unreasonable activation barrier of 99 K, which is well above the activation barrier observed for known single-chain magnets. A second frequency-dependent out-of-phase peak is observed for 4 and 5 at 11 K that is not present in 2 , 3 . This peak is analyzed with the Vogel–Fulcher function, and is attributed to cluster spin-glass interactions. [ABSTRACT FROM AUTHOR]

The measurements of neutron diffraction patterns of commercially product and 10 hour mechanically milled cathode material lithium cobaltites (LiCoO2) have been performed. Rietveld analysis using FullProf does not show the change of crystal structure due to milling process, but the diffraction pattern has a lower intensity and the diffraction-line was broadening. The results of line-broadening study on milled sample using Rietveld methods detected that the microstrain was occurred in the sample with value 0.127080(35) % and the average crystallite size was 424.78(20) Å.

Abstract: The effects of hydrogen absorption on the crystalline and magnetic properties of the γ-phase Y2Co7H6 were examined by bulk magnetic measurements, neutron diffraction and X-ray absorption spectroscopy. An orthorhombic distortion of the unit cell occurs upon hydrogen insertion, accompanied by a reduction of the magnetic moment on Co and a decrease of the ordering temperature. Magnetic measurements indicate a metamagnetic transition occurring in the γ-phase hydride. The transition shows a broad hysteresis and the magnitude of the critical field is found to decrease with increasing temperature. The electronic structure of Co in Y2Co7 and Y2Co7H6 has been investigated by X-ray absorption spectroscopy. The observed decrease of the pre-peak intensities in the Co-K edge XANES spectra are related to the changes of the 4p–3d density of states upon hydrogen insertion. A comparative X-ray magnetic circular dichroism investigation at the Co-K edge has been carried out for Y2Co7 and Y2Co7H6. The observed XMCD signal enables us to propose that ferromagnetic ordering occurs in the γ-hydride. [Copyright &y& Elsevier]

Metal-organic frameworks (MOFs) have recently received increasing interest due to their potential application in the energy storage and conversion field. Herein, cobalt-based layered MOF ({[Co(Hmt)(tfbdc)(H2O)2]·(H2O)2}n, Co-LMOF; Hmt = hexamethylenetetramine; H2tfbdc = 2,3,5,6-tetrafluoroterephthalic acid) has been evaluated as an electrode material for supercapacitors. The Co-LMOF electrode exhibits a high specific capacitance and excellent cycling stability. Its maximum specific capacitance is 2474 F g(-1) at a current density of 1 A g(-1), and the specific capacitance retention is about 94.3% after 2000 cycles. The excellent electrochemical property may be ascribed to the intrinsic nature of Co-LMOF, enough space available for the storage and diffusion of the electrolyte, and the particles of nanoscale size.