Thermogravimetric studies on some Cu(II) amine complexes

Abstract

Thermogravimetric analysis of solid state bis-Cu(II) amine complexes CuL2X2, where X-CI or NO~ and L = ethylenediamina (en), tetramethylethylenediamine (tmn), ophenylenediamine (opd) and 2,2' bipyridyt (bpy), has been Carried out and the kinetic parameters have been determined by fitting the observed mass losses corresponding to various steps using the Coats and Redfern equation. These studies show that the activation energies of these complexes decrease on changing the ligand in the order: bpy >opd > en > tmn. This trend can be attributed to the rigidity of the N~--N skeleton in the bpy and opd ligands and steric crowding at the nitrogens in the tmn ligand. The majority of the decomposition steps were found to be composite in nature and frequently involved fractional groups expelled from the complexes. From the observation of E, > A H, the thermal decomposition process of these complexes appears to be governed by the "nucleation and growth" mechanism.Our studies on the temperature dependence of the electrical conductivity of some solid state bis Cu(II) amine complexes CuLzX 2 where X = CI-or N~) 3 and L = ethylenediamine (en), tetramethylethylenediamine (tmn), o-phenylenediamine (opd) and 2,2' bipyridyl (bpy), exhibited a number of discontinuities in various temperature intervals which are indicative of structural phase changes and/or thermal decomposition. Though the literature on such coordination complexes is quite extensive [1], except for some complexes of Cu(II)SO4 [2], very little is known about their thermal stability. Therefore, in order to understand the reasons for the above-mentioned-discontinuities in the electrical conductivity at various temperatures, the thermal properties of the complexes were studied. ExperimentalThe above-mentioned Cu(II) amine complexes were prepared by treating aqueous alcoholic solutions of CuX 2 (X = C1-or NO~) and the appropriate ligands L (en, tmn, opd, bpy) in the stoichiometric ratio of 1:2 by following procedures similar to those reported in the literature [3]. The complexes were characterised by elemental microanalysis (C, H, N

Thermogravimetric investigation of thermal decomposition of copper(II) complexes with methylpyrido[2,3-d]imidazole derivatives

“…A comparison of the corresponding steps of thermal decomposition of the nitrate and chloride complexes shows that elimination of the organic ligand is slower and occurs at higher temperatures for the chloride complexes than for the nitrate complexes. This suggests that the above replacement must cause an increase in thermal stability of the complex [15,16,19]. This is consistent with the general observation that 'changing the anion has a pronounced effect on the thermal stability of a complex' [15].…”

“…This suggests that the above replacement must cause an increase in thermal stability of the complex [15,16,19]. This is consistent with the general observation that 'changing the anion has a pronounced effect on the thermal stability of a complex' [15]. The difference in thermal stability between the nitrate and chloride complexes of Cu(II) is probably a result of the stability of the electron structure of the chloride anion (octet).…”

“…Table 2 contains the proposed mechanisms for decomposition of the copper(II) complexes investigated. Similar behaviour was observed during heating of nitrate complexes of copper(II) with the amines of bipy, alkyl derivatives of imidazole, ethylenediamine and benzimidazole [15][16][17][18]. Those compounds also decomposed exothermally to Cue, but the elimination of organic ligand molecules was in that case the main process during the first step of decomposition.…”

Precipitation of pertechnetate ion from nitric acid solutions using complexes of copper(II) with heterocyclic N-donor ligands

“…The typical exothermic peak corresponding to this effect is observed at 220-350°C. In this temperatures range the removal of nitrate ions is accompanied by burning of the organic ligands and formation of CuO [24,25]. As shown in [15], decomposition of earlier studied compound Fe(phen) 3 (TcO 4 ) x (NO 3 ) y ÁnH 2 O proceeded in 4 stages, but in the case of Cu(phen) x (TcO 4 ) y (NO 3 ) (2-y) ÁnH 2 O, only two stages were observed.…”

Synthetic and spectroscopic studies of chelate polymers involving azelaoyl bis‐N‐phenyl hydroxamic acid with transition metal ions

“…IR spectra have shown potential bidentate behavior of ligands having complexing sites at hydroxyl and carbonyl groups, which could give rise to complexes of varied coordination numbers depending on the amount of acid used. Recently, a large number of applications for chelate polymers have been reported 1–4. Chelate polymers of hydroxamic acid with high thermal stability were reported by Gandhi et al5…”