New mixed-ligand tetraethyl ammonium halogenocobaltates(II) of general formula [Et4N](2)[CoBrnCl4-n] have been synthesized. Their thermal properties were characterized on the basis of the TG and DTG curves taken in argon and derivatograms recorded in static air. Some products of successive decomposition steps were identified based on their IR, FIR and VIS spectra as well as the results of elemental analysis. The influence of the nature of the complex anion and oven atmosphere on the progress of thermal decomposition of the compounds has been discussed. (c) 2007 Elsevier B.V. All rights reserved.