Structural Evolution of Iron(III) Trifluoroacetate upon Thermal Decomposition: Chains, Layers, and Rings

Abstract

Metal trifluoroacetates (TFAs) are commonplace precursors for bulk and nanostructured metal fluorides and oxides obtained usually through their thermal decomposition. Very little, however, is known about the atomistic mechanism of such a thermal conversion, or even the crystal structure of the precursors. In this study, we detail the structural evolution of Fe(TFA) 3 upon its thermal decomposition into rhombohedral iron(III) fluoride. Several distinct structural motifs have been identified in the temperature range of 250−350 °C. In particular, Fe(TFA) 3 , Fe 2 F(TFA) 5 , and FeF(TFA) 2 are composed of infinite chains. In addition, several volatile molecular species with ring structureFe n F n (TFA) 2n (n = 6−10)have been characterized both by single-crystal X-ray diffraction and by mass spectrometry. Further conversion of TFA groups into fluoride ions leads to a layered FeF 2 (TFA). All these compounds feature bridging TFA ligands and octahedral fluoroor oxo-coordination of Fe. The retention of the +3 oxidation state is confirmed by 57 Fe Mossbauer spectroscopy. Magnetization measurements point to the ferrimagnetic ordering in FeF 2 (TFA) at T ≤ 150 K, unlike Fe(TFA) 3 , which remains paramagnetic at as low as 10 K. This study highlights the potential of metal TFAs for the rational synthesis of molecular and solid-state hybrid compounds by their versatile thermal decomposition into fully inorganic materials.

Electrochemical Formation of a Covalent–Ionic Stage-1 Graphite Intercalation Compound with Trifluoroacetic Acid

“…These signals are unambiguously assigned to the trifluoroacetic acid parent and its fragments. 65 The next decrease in the mass of 16 wt % in the 570−900 °C temperature range reveals the same MS signals, except for the peaks at 97 and 114 amu. This suggests that the signal of the parent CF 3 COOH is not observed at these higher temperatures because of its decarboxylation.…”

“…During this “thermal decomposition” of the GIC550, we detected peaks for atomic mass units (amu) 28 (CO), 44 (CO 2 ), 69 (CF 3 ), 97 (CF 3 CO), and 114 (CF 3 COOH). These signals are unambiguously assigned to the trifluoroacetic acid parent and its fragments . The next decrease in the mass of 16 wt % in the 570–900 °C temperature range reveals the same MS signals, except for the peaks at 97 and 114 amu.…”

Synthesis and combustion inhibition efficiency of iron short-chain perfluorocarboxylates

“…No significant weight loss appeared at 73 °C (the boiling point of TFA), strongly suggesting that no free TFA resided on the FeTFA sample. Wörle et al [47] synthesized iron (III) trifluoroacetate, Fe(TFA)3, by a different synthesis approach to ours. They reported an infinite chain structure of Fe(TFA)3.…”

Reactivity of bi- and monometallic trifluoroacetates towards amorphous SiO2

“…The stepwise replacement of trifluoroacetato ligands by fluoride anions has been observed in the thermolysis of Fe(tfa) 3 . 39 From a structural standpoint, the connectivity of metal atoms in K 4 Mn 3 (tfa) 9 F and K 2 Mn(tfa) 3 F may be regarded as intermediate between that observed in bimetallic trifluoroacetates and fluoroperovskites. For clarity, the crystal structure of cubic KMnF 3 is shown in Fig.…”