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

Variable-temperature Fe-57 Mossbauer 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 (FMDMACI), was prepared and studied both prior End subsequent to exchange 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 Angstrom was thermally stable up to 200 degrees C in air. TP-SIP-MS indicated that a small proportion of the incorporated metallocene was volatilised at temperatures below 400 degrees 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). Fe-57 Mossbauer 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, delta, and quadrupole splitting, Delta, of the incorporated metallocene were essentially the same in all complexes and virtually identical to that observed for FMDMACI (delta = 0.34 mm s(-1), Delta = 2.32 mm s(-1) at 300 K). The values for the Debye temperature theta(D) and recoil-free fraction f determined from variable-temperature Fe-57 Mossbauer spectroscopy, were typically 140 K and 0.12, respectively, for FMDMACI 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-Al-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.