Kinetics of Multi-Step Processes of Thermal Degradation of Co(II) Complex With N-Benzyloxycarbonylglycinato Ligand. Deconvolution of DTG Curves

Thermal decomposition of Co(II) complex with N-benzyloxycarbonylglycinato ligand, [Co(N-Boc-gly)(2)(H2O)(4)]center dot 2H(2)O, in non-isothermal conditions occurs in three complex steps. In order to investigate detail kinetics of first two steps, dehydration and ligand degradation, DTG curves were deconvoluted using product of Gaussian and Lorentzian function. It was shown that process of complex dehydration consists of three, while process of ligand fragmentation consist of five elementary steps. For elementary steps the kinetic triplet (E-a, Z and f(alpha)) was determinated. Kinetic parameters were obtained by application of IKP method. On the basis of Malek's criteria and Sestak-Berggren's method, Sestak-Berggren's model, f(alpha)=alpha(M)(1-alpha)(N) was suggested for all elementary steps, while Master plot method and Perez-Maqueda criteria confirmed suggested reaction models. The thermodynamic activation parameters were calculated for process of complex dehydration, and lifetime for first elementary step of the dehydration and ligand degradation processes was estimated

Biologically active dinuclear complexes of cobalt(II) with a pendant octaazamacrocyclic ligand and pseudohalides

In the three newly-prepared mixed dinuclear penta-coordinated cobalt(II) complexes, with the pendant macrocyclic ligand N,N',N ",N"'-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and pseudohalides, of the general formula [Co-2(NCY)(n)tpmc](ClO4)(4) (n)(Y = O, n = 1; Y = S, Se, n = 2), the NCO group is bridging, and the other two pseudohalides are nonbridging, i.e., singly coordinated to each metal in the trans position. It can be supposed that the pendant ligand assumes the boat conformation, in complex involving the cyanate ligand whereas it is in the chair conformation in the complexes involving the thiocyanate and selenocyanate ligands. It was found that these complexes exhibit biological activity towards the following strains of microorganisms: Esherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Bacillus thuringiensis (ssp. kurstaki), Pseudomonas aeruginosa (ATCC 27853) and Candida albicans

Kinetics and mechanism of structural transformations of 2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-N-(2-phenylethyl)-ethanamide during heating

The kinetics and mechanism of the structural transformation of 2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-N-(2-phenylethyl)-ethanamide in non-isothermal conditions were studied by using isoconversion as well as non-isoconversion techniques. It was shown that the crystal, Z-form of compound, was stable in the temperature range from room temperature to melting point, when E-form of compound was formed. This process involves the breaking of crystal structure and the forming of glass material as a new phase, which by cooling forms crystal of the E-form of compound very slowly. The dependences of kinetic parameters on fractional extent conversion were determined indicating a very complex process which involves more than one elementary step, as can be expected for most solid state reactions. The possible mechanism of the process was discussed according to the algorithm concerning the form of these dependences. The evaluation of kinetics parameters and isokinetic relationships were done by combination of model fitting and model-free approach

Thermal degradation of coordination polymer [Cd(N-Boc-gly)(2)(H2O)(2)](n)

Multi-step thermal degradation of coordination polymer [Cd(N-Boc-gly)(2)(H2O)(2)](n) in non-isothermal conditions was studied. The kinetic parameters were determined from the thermal decomposition data using the isoconversion and non-isoconversion techniques. It was shown that the coordination polymer is stable up to 60 C, when the multi-step process of thermal dehydration, followed by steps of degradation, starts. The kinetic triplet for the step of dehydration was established as f(alpha) = 3/2(1 - alpha)(2/3)[1 - (1 - alpha)(1/3)](-1). E-inv = 170.4 +/- 6.4 kJ mol(-1) and Z(inv) =2.6 x 10(23). The established kinetic model, known as "D3 model", was confirmed by application criteria defined by Malek, Perez-Maqueda et al. as well as Master plot method. Dehydration step is followed by two steps of dehydrated coordination polymer degradation. On the base of the dependence of Arrhenius parameters (E-a and Z) on conversion degree (alpha), the mechanisms of degradation were discussed. In this way it was shown that second and third steps of degradation of coordination polymer are complex involving more than one elementary step. The second step corresponds to the loss of two C6H5CH2O- fragments in two parallel steps. The third step of degradation, ascribed to the loss of two -C(=O)NHCH2- fragments, is complicated by changing kinetically to diffusion control. (C) 2011 Elsevier B.V. All rights reserved

Kinetics and mechanism of degradation of Co(II)-N-benzyloxycarbonylglycinato complex

The kinetics of multi-step thermal degradation of Co(II) complex with N-benzyloxycarbonyl glycinato ligand [Co(N-Boc-gly)(2)(H2O)(4)]center dot 2H(2)O, in non-isothermal conditions was studied using isoconversional and non-isoconversional methods. The degradation of complex occurs in three well-separated steps involving the loss of water molecules in first step followed by two degradation steps of dehydrated complex. The dependence of Arrhenius parameters on conversion degree showed that all observed steps of thermal degradation are very complex, involving more than one elementary step, as can be expected for most solid-state heterogeneous reactions with solid reactants and solid and gaseous products. It was shown that step 1, corresponding to the dehydration, involves a series of competitive dehydration steps of differently bound water molecules complicated by diffusion. Second step involves two parallel reactions related to the loss of two identical C6H5CH2O-ligand fragments complicated by the presence of products in gaseous state. Further degradation in step 3 corresponds to complex process with a change in the limiting stage, in this case from the kinetic to the diffusion regime, connected with the presence of gaseous products diffusing through the solid product

Thermal stability and degradation of Co(II), Cd(II), and Zn(II) complexes with N-benzyloxycarbonylglycinato ligand

Thermal behavior of Co(II), Cd(II), and Zn(II) complexes with N-benzyloxycarbonylglycinato ligand was investigated using the results of TG, DSC and DTG analysis obtained at different heating rates (2.5 to 30 A degrees C min(-1)), from room temperature to about 900 A degrees C. Mechanisms of complex degradation, as well as enthalpies of the degradation processes were determined. It is shown that thermal stability of investigated complexes correlates with their crystal structures, especially with the presence of crystallization and coordinated water molecules. The values of dehydration enthalpies are discussed and correlated with composition of the complexes. Kissinger's, Ozawa's, and Friedman's isoconversion methods were used for the determination of kinetic parameters: the pre-exponential factor A and the apparent activation energy E (a). For all three complexes and all steps of degradation, the values of kinetics parameters obtained by Kissinger's and Ozawa's methods are in good agreement. The results obtained by Friedman's method showed that some decomposition steps are simple and some others are complex ones