K. Turvey

Thermal and electrical studies on quinoxaline compounds of some first row transition metal ions

Abstract The chloro and bromo compounds of quinoxaline with manganese(II), cobalt(II), nickel(II) and copper(II) have been prepared in ethanolic solution. The thermal behaviour of these compounds was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The thermal decomposition studies show that the compounds dichlorobis(quinoxaline) cobalt(II), dibromobis(quinoxaline) cobalt(II) and dibromobis(quinoxaline) manganese(II) form intermediate compounds before the metal halide is produced. The other compounds undergo decomposition with loss of organic ligand and the formation of the metal halide. Electrical conductivities at room temperature range from 1.4 × 10 −6 Ω −1 m −1 for MnCl 2 Q to 2.3 × 10 −3 Ω −1 m −1 for both CoCl 2 Q 2 and CoBr 2 Q 2 . There appears to be a correlation between electrical conductivity and coordination number of the metal atom. From the temperature dependence of conductivity, information has been obtained for donor or acceptor ionization energies. Decomposition temperature, as electrically determined, is in good agreement with the TG method.

Thermal and electrical studies on pyrazine-2,3-dicarboxylic acid compounds of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II)

Abstract Some new compounds of pyrazine-2,3-dicarboxylic acid with manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) have been prepared in aqueous solution. The thermal behaviour of these compounds has been studied by thermogravimetry (TG), and differential scanning calorimetry (DSC) techniques. The compounds are all hydrated. Thermal decomposition studies show that these compounds lose water followed by organic ligand to give the metal oxide. Electrical conductivity measurements were made at room temperature. Ohmic and space charge limited conduction is observed. A current component opposing the applied voltage is observed in the compounds, with the exception of the copper compound.

Thermal and electrical studies on porphyrin compounds of cobalt(II), copper(II) and zinc(II)

Abstract Thermogravimetric and differential thermal analysis data are reported for 5,10,15,20-tetraphenyl-21 H ,23 H -porphine metal(II) complexes where the metal is cobalt, copper and zinc. Similar data are also reported for 5,10,15,20-tetrakis(4-methoxyphenyl)-21 H ,23 H -porphine cobalt(II). For the above compounds the electrical conductivities have been measured. There is evidence for space-charge limited conduction, and conductivities at room temperature under an applied field of 1×10 4 V m −1 are all within a factor of two either side of 2×l0 −8 Ω −1 m −1 . Activation energies for forming free carriers have been measured from the temperature dependence of the electrical conductivities.

Thermal, electrical and structural properties of chloro complexes of cobalt, nickel, copper and zinc with 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline

Abstract Some new compounds of 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline with cobalt(II), nickel(II), copper(II) and zinc(II) have been prepared in toluene. The cobalt and zinc compounds have tetrahedral structures while the nickel and copper complexes have octahedral structures. The thermal behaviour of these compounds has been studied by thermogravimetry and differential thermal analysis. Each compound is highly stable and decomposes, without formation of any intermediate compounds, to the metal oxide. The room temperature conductivities of the prepared compounds are all in the range 3.4 × 10−8 Ω−1 m−1 to 2.2 × 10−7 Ω−1 m−1. Evidence is advanced from current-voltage data and, more especially, from attenuated total reflectance spectra taken during application of an electric field, that the compounds undergo significant field-induced distortion that remains after removal of the field.

Thermal, spectral, magnetic and electrical studies of cobalt(II) and nickel(II) with 3-(3-pyridyl)acrylic acid

Abstract The preparation and some properties of the complexes of 3-(3-pyridyl)acrylic acid with cobalt and nickel are described. Spectral, magnetic and solubility studies show that the complexes, which are hydrated, have polymeric octahedral structures. The thermal behaviour of these compounds has been studied by thermogravimetry (TG) and differential thermal analysis (DTA). Thermal decomposition studies show that the compounds lose water of crystallization followed by organic ligand to give the metal oxide. Electrical conductivity measurements at room temperature give results of 1.00×10 −6 Ω −1 m −1 and (1.6 ± 0.4)×10 −4 Ω −1 m −1 for the cobalt and nickel complexes respectively. The current-voltage characteristics exhibit hysteresis, which is very marked for the nickel compound, and is attributed to current arising from dipolar orientation superimposed on a conduction current.

Structural, thermal and electrical studies of complexes of silicon with some first row transition elements

Mixed metal compounds of the main group element silicon and the first row transition elements iron, cobalt, copper and zinc have been prepared. The vibrational spectra, electronic spectra and some magnetic properties are reported for the compounds. The thermal behaviour of each compound has been studied using thermogravimetry. It is found that a mixed metal oxide is formed on decomposition for each compound. Electrical measurements are reported, including determinations of the conductivity and activation energy. For the zinc complex the room temperature conductivity is sufficiently high that device applications are a possibility.

Preparation, structural characterisation, thermal and electrical studies of the chloro complexes of cobalt, nickel and copper with acrylamide

Abstract The chloro compounds of cobalt, nickel and copper with acrylamide have been prepared. Spectral and magnetic data have been used to deduce the stereochemistry of the compounds. The thermal behaviour of acrylamide and its complexes with cobalt, nickel and copper have been studied by thermogravimetry and differential thermal analysis. The cobalt complex forms an intermediate complex before the metal oxide is produced. The nickel and copper complexes undergo decomposition with loss of the organic ligand and chlorine to give the metal oxides. Electrical conductivities for the compounds at room-temperature are in the range 5.8 × 10 −8 Ω −1 m −1 (for the cobalt compound) to 3.1 × 10 −5 Ω −1 m −1 (for the copper compound). The current-voltage characteristic for the uncomplexed acrylamide is ohmic whereas its complexes exhibit hysteresis which is attributed to orientation of the polar complexed molecules in the applied electric field. The temperature dependences of conductivity have been determined for the compounds and are used to measure the activation energies for conduction.

Preparation, characterization, thermal and electrical studies of poly(4-vinylpyridine) and its cobalt(II) bromide complex

Abstract A polymer-metal complex was prepared by complexing cobalt bromide with poly(4-vinylpyridine) in aqueous ethanol. Analysis of the complex shows that its formula is [Co(Vpy) 2 Br 2 ·H 2 O] n , where (Vpy) represents a molecule of 4-vinylpyridine. From spectral and magnetic data, the environment of the cobalt atom is found to be tetrahedral. The metal polymer has been further characterized using gel permeation chromatography, differential thermal analysis and thermogravimetry. The electrical conductivity and its temperature dependence were obtained for the cobalt bromide complex and for poly(4-vinylpyridine). From this work and comparison with earlier work on cobalt chloride complexes of poly(4-vinylpyridine), it is concluded that the metal and halogen atoms play only minor roles in the electrical properties.

Preparation, structural characterisation, and thermal and electrical studies of complexes of cobalt, nickel and zinc with 2,3-pyrazinedicarboxamide

Abstract Compounds of 2,3-pyrazinedicarboxamide with cobalt, nickel and zinc were prepared and isolated from aqueous solution. Spectral and magnetic studies showed that the cobalt and nickel compounds have octahedral structures while the zinc compound has a tetrahedral structure. The thermal behaviour of these compounds was studied by thermogravimetry and differential thermal analysis. The compounds are hydrated and they decompose thermally by losing water, followed by organic ligand, to give the metal oxide. Room temperature electrical conductivity measurements give results in the range 8.2 × 10 −8 Ω −1 m −1 to 1.3 × 10 −7 Ω −1 m −1 for the prepared compounds. A correlation between structure and electrical properties is apparent because the two complexes in which the metal environment is octahedral (i.e. the cobalt and nickel complexes) exhibit a polarity effect not observed for the zinc complex (in which the metal environment is tetrahedral). The effect is an increase in conductivity on reversal of the applied polarity but the increased conductivity remains on reinstatement of the initial polarity. The temperature dependence of the conductivity was obtained for each compound and used to infer an approximate activation energy for conduction.

Thermal, structural and electrical studies of the chloro complexes of cobalt, nickel, copper and zinc with 2-methylquinoxaline

Abstract The chloro compounds of 2-methylquinoxaline (MeQ) with cobalt(II), nickel(II), copper(II) and zine(II) were prepared in ethanolic solution from which the solid compounds were isolated. The suggested structure for the cobalt and zinc compounds is tetrahedral, while for the nickel and copper compounds it is octahedral. The techniques of thermogravimetry and differential thermal analysis show that the compounds Co(MeQ) 2 Cl 2 and Ni(MeQ) 2 Cl 2 form intermediate compounds before the metal halide is produced. The compound Cu(MeQ)Cl 2 undergoes decomposition with loss of the 2-methylquinoxaline and the formation of copper(II) chloride, while the compound Zn(MeQ) 2 Cl 2 decomposes with loss of the 2-methylquinoxaline and chlorine and the formation of zinc oxide. From the electrical measurements on the compounds isolated from ethanolic solution, it was found that two distinct groups exist: Co(MeQ) 2 Cl 2 and Ni(MeQ) 2 Cl 2 have nearly equal and relatively high conductivities, whilst Cu(MeQ)Cl 2 and Zn(MeQ) 2 Cl 2 have nearly equal but relatively low conductivities. Within each group the temperature dependence of electrical conductivity is similar but it differs between the groups.