Organometallic cation-exchanged phyllosilicates: variable-temperature 57Fe Mössbauer spectroscopic and related studies of the adsorption of dimethylaminomethylferrocene on clays and pillared clays

Abstract

Variable-temperature ⁵⁷Fe Mössbauer spectroscopy, thermogravimetry (TG), powder X-ray diffraction (PXRD) and temperature-programmed solid insertion probe mass spectrometry (TP-SIP-MS) have been used to study the interaction of dimethylaminomethylferrocene (DMAMF) with Westone-L (WL), a low iron montmorillonite. The hydrochloride salt of DMAMF, (ferrocenylmethyl)dimethylammonium chloride (FMDMACl), was prepared and studied both prior and subsequent toexchange on the interlamellar sites of WL. X-Ray diffraction confirmed that the FMDMA⁺ cations were incorporated between the clay lamellae and the observed spacing of 15.1 Å was thermally stable up to 200 °C in air. TP-SIP-MS indicated that a small proportion of the incorporated metallocene was volatilised at temperatures below 400 °C, but that the majority decomposed via loss of cyclopentadienyl ligands leaving the metal centre between the sheets. A similar thermal degradation path was observed for DMAMF on aluminium pillared clay (Al-PILC). ⁵⁷Fe Mössbauer spectroscopy revealed that the FMDMA⁺ cation occupied a similar environment in the chloride salt, FMDMA⁺–WL and DMAMF–Al-PILC insofar as the isomer shift, 6, and quadrupole splitting, Δ, of the incorporated metallocene were essentially the same in all complexes and virtually identical to that observed for FMDMACl(δ= 0.34 mm s^–l, δ= 2.32 mm s^–l at 300 K). The values for the Debye temperature θ, and recoil-free fraction f determined from variable-temperature ⁵⁷Fe Mössbauer spectroscopy, were typically 140 K and 0.12, respectively, for FMDMACl and FMDMA⁺–WL, thus confirming the similar environment occupied by the cation in the chloride salt and in WL. In contrast, the corresponding values for DMAMF–A1-PILC were 118 K and 0.06, respectively, indicating that the the metallocene enjoyed much greater freedom in the galleries of the Al-PILC which exceed the dimensions of the metallocene compared to FMDMA⁺-WL where the organoiron cation itself determines the layer separation.