Density functional theory assessment of the thermal degradation of diclofenac and its calcium and iron complexes

Thermogravimetric analyses of diclofenac sodium, its Ca2C and Fe3C complexes manifested a decreasing trend of the onset decomposition temperatures at which these compounds dissociated. The drop in the temperature was metal ion dependent; the sodium salt showed thermal stability up to 245 8C, whereas the complexes started their degradation processes at temperatures starting from 90 8C. While G* for the cleavage of the acetate moiety in the sodium salt was 63.76 kJmolK1, it was 82.06 and 140.57 kJmolK1 in the cases of Ca2C and Fe3C, respectively. However, their complete fusion took place at 187.65, 150.34 and 98.77 8C, respectively, displaying a reversed trend which is probably indicative of some catalytic part on the binding metals. Using the Gaussian 98 W package of programs, ab initio molecular orbital treatments were applied to diclofenac and its Ca2C and Fe3C metal complexes to study their electronic structure at the atomic level. The thermochemistry of diclofenac sodium was followed through the TG fragmentation peak temperatures using the density functional theory calculations at the 6-31G(d) basis set level. The FT-IR data were in good agreement with the theoretically calculated values. Single point calculations at the B3LYP/ 6-311G(d) level of theory, were used to compare the geometric features, energies and dipole moments of these compounds to detect the effect of the binding metal ions on the thermal dissociation of their diclofenac complexes. q 2005 Elsevier B.V. All rights reserved.