Organometallic cation-exchanged phyllosilicates:57Fe Mössbauer spectroscopic study of organoiron complexes on a low-iron montmorillonite

Variable-temperature 57Fe Mossbauer spectroscopy, thermogravimetry and powder X-ray diffraction have been used to study the cations tricarbonyl(η5–2,4-dimethylcyclohexadienyl)iron(1+) and tricarbonyl(η5–2-methoxycyclohexadienyl)iron(1+) as both the hexafluorophosphate salts (A1 and A2, respectively) and when cation-exchanged onto the interlamellar sites of Westone-L (W-L), a low-iron montmorillonite (denoted A1-W-L and A2-W-L, respectively). A combination of thermogravimetry, total carbon analysis and X-ray fluorescence analysis for iron indicated that 40% of the available exchange sites on W-L were occupied by the cyclohexadienyl cations. The isomer shift, δ, and quadrupole splitting, Δ, of both A1 (δ= 0.02 mm s–1; Δ= 1.56 mm s–1) and A2 (δ= 0.02 mm s–1; Δ= 1.47 mm s–1) were unaffected by incorporation of the cations into the interlamellar environment. The hexafluorophosphate salts, A1 and A2, exhibited similar Debye temperatures, θD, and recoilless fractions, f, of 160 ± 2 K and 0.61, respectively, indicating that both iron moities enjoyed the same amount of freedom in the parent salt. In contrast, the values of θD and f for A2-W-L (140 K and 0.54, respectively) were both higher than for A1-W-L (131 K and 0.49), indicating that A2 was held more tightly in the interlamellar environment than A1.