The thermal decomposition reactions of bis-(pyridine-2-aldoxime)-copper(II) complexes

Abstract

The thermal properties of some complexes of copper(l I) with pyridine-2-atdoxime (HPAO), where the ligand appears either as the ion (PAO-) or as a neutral molecule, were determined in vacuo and in dynamic nitrogen and oxygen gas atmospheres. The study was carried out by thermoanalytical (TG, DTG. DTA), spectroscopic and spectrometric (UVvisible, IR, diffuse reflectance, mass) techniques.The initial decomposition temperature is influenced by the number of acid hydrogens in the complex; the thermal stability sequence in vacuo is:The thermal decomposition reactions occur in several separate steps, the first of which gives rise to partial ligand decomposition, the reduction of copper(ll) to copper(I), and the conversion of the residual pyridine-2-aldoxime into acid amide.Several papers have been published on the complexes of metal ions with pyridine-2--aldoxime (CsH6N20; HPAO). Some copper(l I) complexes with this ligand have been studied in aqueous solution, or precipitated and characterized using IR, diffuse reflectance, polarographic and potentiometric techniques [1][2][3][4][5][6][7], but no data have been reported on the thermal stabilities and decomposition reactions.Following thermoanalytical studies of the complexes of 3 d metal ions with organic ligands [8][9][10][11], in this paper we report results on the thermal behaviour of the complexes [Cu(C6H5N20)2Hn]CI n (where n = 0, 1 or 2). The study has been carried out by thermogravimetry, differential thermal analysis and mass spectrometry; the proposed decomposition mechanisms are supported by analysis of the stable intermediates obtained by interruption of the heating of the samples at the appropriate temperatures. Experimenta I ApparatusThe thermal measurements were carried out by means of a Perkin-Elmer TGS-2 thermal analyser and DTA 1700. TG runs were made in vacuo and in dynamic nitrogen

An investigation of some homo- and heterobinuclear complexes of copper(II) and nickel(II) with pyridine-2-aldoxime

“…was prepared and analysed as described earlier [2]. A 0.1% aqueous solution of the complex is green and its pH is about 4.3; increasing the pH of this solution the absorption maximum at 596 nm is shifted bathochromically to 628 nm with hyperchromic effect.…”

“…The light-blue-green precipitate, which forms rapidly, was filtered, washed with ethanol first and then with diethyl ether; finally dried in vacuo over silica gel. The results of analysis, performed as described [2], were in agreement with the proposed formula; the nickel content was determined by atomic absorption spectrophotometry. A 0.1% aqueous solution of the complex is pale yellow and its pH is about 3.8; increasing the pH of the solution the colour turns to orange-yellow and its intensity increases to pH = 7.5 and then decreases.…”

“…Following thermoanalytical studies of the complexes of 3d metal ions with pyridinea!doximes [2,3], the present investigation is concerned with homo-and heterobinuclear chelates obtained by the reaction of the "metal-complex" chelating agents c/s bis(pyridine-2-aldoxime) copper(II) and nickel(II) with the ions of the same metals.…”

Spectral and thermal studies of copper(II) complexes of 3- and 4-pyridinealdoxime

“…The slight solubility in water and the hydrolysis of both complexes at about pH 6 [2], however, prevented determination of the ionizaion constants and the synthesis of monohydrogen-and bis(pyridinealdoxime)copper(II) complexes, as occurs with pyridine-2-aldoxime as ligand [1].…”

“…In a recent paper [1] we reported in detail the thermal decompositions of three bis(pyridine-2-aldoxime)copper(II) complexes of the type [Cu(Py2--CHNO)2H,]C1. (where n = 0, 1 or 2).…”