The IR, far-IR, Raman and Mossbauer spectra have been utilized to identify a new compound consisting of a tetrachloroferrate(III) anion and a tetrabutylammonium cation [(C4H9)(4)N][FeCl4]. Its degradation has been studied by thermal analysis using TG, TG-MS, DTG and DTA, as well as DSC techniques. The measurements were run in static air and in argon atmosphere. Solid residues were identified by elemental analysis, far-IR and Mossbauer spectroscopy. The discussion was focused on processes proceeding during the first step of the thermal decomposition. (C) 2005 Elsevier B.V. All rights reserved.