No abstract

Inclusion complexes of ferrocene (Fc) with cucurbit[n]urils (n = 7, 8) have been prepared via a rapid microwave-assisted hydrothermal approach. Solids were isolated and characterised by elemental analysis, powder X-ray diffraction (PXRD), spectroscopic, and thermoanalytical methods. The UV-Vis spectra support the presence of Fc in Fc@CB7 and a mixture of Fc and ferrocenium ions in Fc@CB8. Partial oxidation of Fc to Fc takes place in situ mainly due to the presence of acid of crystallisation in CB8. On the basis of PXRD, the complex Fc@CB8 is classified into an isostructural series that is formed by several CB8-containing compounds that crystallise in the space group I4/a and have similar unit cell dimensions and CB8 packing motifs. The FT-IR and Raman spectra of Fc@CB7 are compared with those of the CB7 host and the Fc guest starting materials, revealing significant frequency shifts of some Fc-centered vibrational modes upon complexation. Blueshifts of the Fe-Cp stretching and ring tilt bands are attributed to encapsulation of Fc monomers in a constrained environment, leading to restricted motion effects and/or a change in the Fc conformation from staggered to eclipsed. The absence of comparable shifts for Fc@CB8 point to a weaker host-guest interaction as a consequence of the larger cavity size. The different host-guest interactions are also evident through a comparison of the C{H} CP MAS NMR spectra. Thermogravimetric analysis for the inclusion compounds reveals that sublimation of Fc is inhibited by molecular encapsulation to the extent that oxidative decomposition of the organoiron species takes place concurrently with cucurbituril decomposition, leading to the formation of hematite, α-FeO.

The photoactivatable CO-releasing molecule (photo-CORM) [Mo(CO) 3 (CNCH 2 COOH) 3 ] (ALF795) has been incorporated into a Zn,Al layered double hydroxide (LDH) host by a coprecipitation synthesis strategy. Powder X-ray diffraction (PXRD) of the resultant material Zn,Al-ALF795 showed that the ALF795 guest molecules assembled into a monolayer to give a basal spacing of 16.0 Å. FTIR and 13 C{ 1 H} CP MAS NMR spectroscopy confirmed that the molecular structure of the tricarbonyl complex was retained upon intercalation. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and elemental analyses confirmed the phase-purity of Zn,Al-ALF795.

Temperature-dependent Fe Mössbauer effect (ME) spectroscopic studies were carried out on ferrocene (Fc), 1,1'-dimethylferrocene (1,1'(CH)Fc) and ferrocenium hexafluorophosphate (FcPF) guest species in cucurbit[n]uril (n = 7, 8) inclusion complexes. The solid inclusion complexes were isolated by freeze-drying of dilute aqueous solutions and/or microwave-assisted precipitation from concentrated mixtures. The presence of genuine 1 : 1 (host : guest) inclusion complexes in the isolated solids was supported by liquid-state H and solid-stateC{H} MAS NMR, elemental and thermogravimetric analyses, powder X-ray diffraction, FTIR spectroscopy, and diffuse reflectance UV-Vis spectroscopy. The ME spectra of the complexes CB7·Fc and CB7·1,1'(CH)Fc consist of well-resolved doublets with hyperfine parameters (isomer shift and quadrupole splitting at 90 K) and temperature-dependent recoil-free fraction data that are very similar to those for the neat parent compounds, Fc and 1,1'(CH)Fc, suggesting that the organometallic guest molecules do not interact significantly with the host environment over the experimental temperature range. The ME spectra for CB7·FcPF and CB8·FcPF consist of a major broad line resonance attributed to a paramagnetic Fe site. From the temperature-dependence of the recoil-free fraction it is evident that the charged guest species in these systems interact with the host environment significantly more strongly than was observed in the case of the neutral guest species, Fc and 1,1'(CH)Fc. Moreover, the ME data indicate that the vibrational amplitude of the ferrocenium guest molecule is significantly larger in the CB8 host molecule than in the CB7 homologue, as expected on the basis of the different cavity sizes.

The catalyst can be recyled, but its activity decreases significantly in consecutive catalytic cycles.