Novel chelates of Pd(II) dithiocarbamates. Spectroscopic studies and thermal behaviour

Abstract

Complexes of Pd(II) with dithiocarbamate derived from α-amino acid (glycine, DL-alanine, DL-valine, L-valine and DL-leucine) have been synthesized. The complexes have been characterized by chemical analysis, infrared, electronic, 1H and 13C NMR and X-ray photoelectron spectroscopies, magnetic susceptibilities measurements, mass spectrometry and TG and DSC analysis. The stoichiometry of these complexes is Pd:L = 1:2 and coordination around the metallic cation seems to be distorted square planar, close to D 2 h . Coordination takes place through the sulphur atoms of the ligands and the carboxylic group is in a free, acidic form. Both sulphur atoms are chemically equivalent, according to the XPS results. 1H and 13C NMR spectra for the DL- and L-valine derivatives indicate that different complexes DD, DL and DL do not have any spectroscopic difference due to the large distance between the chiral centers. Thermal decomposition of the complexes takes place through a multi-step process, the first step being a decarboxylation, followed by a complex pyrolysis that leads to palladium oxide. The thermal stability of these complexes decreases in the order Pd(dtc- DL- val) 2 > Pd(dtc- DL-ala) 2 > Pd(dtc-gly) 2 > Pd(dtc- DL- leu) 2. The mass spectrometric data indicate that the [S 2CNHCH 2COO] + ion is formed in all cases, with the final formation of [S 2C] + for the ligands. For the complexes, however, the species [S-C-ala] +, [S-C-val] + and [S-C-leu] + are formed.