J.E. House

A proposed mechanism for the thermal reactions in solid complexes

Abstract A general mechanism is proposed for solid state reactions of coordination compounds in which the generations of a point defect is considered as the formation of the transition state. Three types of defects are considered which may apply in different types of reactions. The types of point defects considered are analogous to the Schottky, Frenkel, and substituted ion types occurring in simple crystals. Intramolecular racemization of (+)—[Co(en) 3 ]X 3 (X = Cl, Br, SCN, or I) is shown to be consistent with the substituted ion type of defect, while dehydration of [Cr(NH 3 ) 5 H 2 O]X 3 complexes is consistent with the formation of a Frenkel type of defect. Energy of the formation of the transition state is discussed in terms of lattice energy and ionic radii.

A TG study of the kinetics of decomposition of ammonium carbonate and ammonium bibarbonate

Abstract The decomposition of ammonium carbonate and ammonium bicarbonate has been studied by TG. In each case, the reactions follow first order kinetics most closely. For the carbonate, the activation energy for decomposition is 85.73 = 6.02 kJ mole −1 , while that of the bicarbonate is 86.19 ± 7.78 kJ mole −1 . Since both solids decompose to give only gaseous products, the largest possible mass loss is observed resulting in minimal experimental error. These reactions have thus served as models and have permitted an accurate assessment of the effects of equation variables on derived kinetic constants.

Thermal studies on solid complexes of silver nitrate with substituted pyridines

Abstract The kinetics of decomposition of several solid complexes of silver nitrate with substituted pyridines has been studied. Activation energies have been determined and, in general, show an increase with increasing basicity of the ligands. A linear relationship exists between the logarithm of the rate constants for decomposition at 400°K and the pKa values of the bases, except for those containing a substituent in the 4-position. Complexes of 2,4- and 3,4-dimethylpyridine are less stable than expected based on pKa values of the bases, and the complex with 4-cyanopyridine is more stable than expected from the basicity of the ligand. These observations are discussed in terms of the nature of the metal-ligand bond.

Kinetic analysis of the dehydration of potassium bis (oxalato)cuprate(II) dihydrate

The dehydration of potassium bis(oxalato)cuprate(II) dihydrate, K2([Cu(C2O4)2] · 2H2O, has been studied isothermally and nonisothermally using TG. To determine the rate law for this reaction, the data from isothermal studies were analyzed according to 17 different rate laws. The data from nonisothermal experiments were analyzed by the procedure of Reich and Stivala. It was found that while an Avrami (nucleation) rate law with n = 2 gives the best fit most frequently, considerable run to run variation exists for both types of experiments. There is general agreement on the most likely mechanism from isothermal and nonisothermal experiments, but the two methods were not consistent with respect to the next most likely mechanism.

Solid state deamination of tris(ethylenediamine)- and tris(propylenediamine)chromium complexes

Abstract The deamination of solid [Cr(en)3] (NCS)3, [Cr(pn)3] (NCS)3 and [Cr(pn)3]Cl3 has been investigated using differential scanning calorimetry. Both the catalyzed and the uncatalyzed reactions have been studied and thermal parameters have been determined for these processes. It was found that while NH4SCN lowers the activation energy for the deamination of [Cr(en)3] (NCS)3 by about 14 kcal/mole, NH4Cl lowers the activation energy by about 6 kcal/mole.

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

Abstract The decomposition of solid K3[Fe(C2O4)3] · 2 H2O and K3[Cr(C2O4)3] · 3 H2O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO2 and additional CO, and finally the loss of CO2. The final product appears to be either K3CrO3 or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K3[Fe(C2O4)3] · 2 H2O, dehydration is followed by the loss of CO2 and CO, CO2 alone, and finally CO. The final product appears to be a basic carbonate of the type K3[FE(O)2(CO3)]. Kinetic and thermal data are presented for most of these decomposition reactions.

Thermal studies on yttrium, neodymium and holmium oxalates

Abstract The thermal decomposition patterns of Y 2 (C 2 O 4 ) 3 · 9 H 2 O, Nd 2 (C 2 O 4 ) 3 · 10 H 2 O and Ho 2 (C 2 O 4 ) 3 · 5.5 H 2 O have been studied using TG and DTG. The hydrated neodymium oxalate loses all the water of hydration in one step to give the anhydrous oxalate while Y 2 (C 2 O 4 ) 3 · 9 H 2 O and Ho 2 (C 2 O 4 ) 3 · 5.5 H 2 O involve four or more dehydration steps to yield the anhydrous oxalates. Further heating of the anhydrous oxalates results in the loss of CO 2 and CO to give the stable metal oxides.

Numerical relationships for temperature integrals with temperature dependent frequency factors

Abstract Temperature integrals having a negative exponent (m) on temperature have been evaluated for m= − 1 2 . −1. − 3 2 . and −2 with E=30–100 kcal mole−1 and T = 300–1000 K. For a given value of m. −log I is linearly related to E and l/T. The slopes and intercepts of these linear equations have been found to be functions of E and T. Also, a linear relationship exists between −log I and m for given values of E and T. By combining these results with those previously published for temperature integrals having positive values of m, equations have been obtained that permit accurate evaluation of temperature integrals for any combination of m. E. and T values.

Decomposition of cis-and trans- potassium diaquobis(oxalato)chromate(III)

Abstract The decomposition of cis - and trans -K[Cr(C 2 O 4 ) 2 ](H 2 O) 2 ] has been studied using differential scanning calorimetry. Dehydration occurs as the first step with activation energies being 27.5 and 13.9 mol −1 , respectively, for the cis and trans complexes. After dehydration, continued heating results in loss of CO amd CO 2 . For the trans complex, an additional endothermic peak is seen and the mass loss indicated that CO has been lost in a single step. In both cases, the final product indicated by mass loss data is KCrO 2 .

An analysis of the Reich and Stivala algorithm for determining the reaction mechanism from TG data

Abstract The mechanisms indicated by the Reich and Stivala algorithm were evaluated for the decomposition of (NH 4 ) 2 CO 3 , NH 4 HCO 3 , and trans -[Co(NH 3 ) 4 Cl 2 ]BrO 3 ·H 2 O. Different mechanisms are indicated when data from different TG runs are used. Also, the data points selected within the same two runs influence the type of mechanism that best represents the data. Apparently, sample-to-sample variations can preclude the unambiguous assignment of a mechanism.