New solid heavy metal complexes with 4-chloro-2-methylphenoxyacetic acid (MCPA) of the general formulae: Pb(MCPA)(2) . H H2O and Cd(MCPA)(2).2H(2)O have been prepared. Diffractometric, IR spectroscopic and thermal analyses of these complexes and the previously described Cu(MCPA)(2) have been performed. The complexes have different structures, a low level of crystallinity and exhibit a tendency to form polymers. An attempt has been made to explain the mode of the ligand molecule coordination on the basis of the position of the bands of the characteristic upsilon(asym) and upsilon(sym) vibrations of the carboxylate croup. The course of the TG, DTG and DTA curves indicates that the compounds decompose in two (the copper salt) or three stages. The decomposition of the cadmium complex is preceded by dehydration. The basic gaseous products of decomposition are H2O and CO2. HCOOH, HOCH2COOH, HCl and trace amounts of compounds containing an aromatic ring were also detected. The final solid decomposition product is a metal oxide. (C) 2003 Elsevier B.V. All rights reserved.