Solid-state study of the structure and host–guest chemistry of cucurbituril-ferrocene inclusion complexes

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.

Inclusion complexes of cucurbit[n]urils (n = 7, 8) with η5‐cyclopentadienyl methyl tricarbonyl molybdenum(II) and their use in epoxidation catalysis

“…PXRD confirmed the poorly crystalline nature of the as-synthesized CB7 sample (Figure 2b). It is noteworthy, however, that the trace matches with the intensity envelope observed in the PXRD pattern of a more crystalline CB7 sample reported previously, 20 order. The compound 1@CB7 also produced a halo pattern characteristic of an amorphous solid (Figure 2c).…”

Evaluation of the supramolecular interaction of Congo red with cucurbiturils using mass spectrometry and spectroscopic methods

“…S4, ESI †). These reflections do not match with those of the as-prepared CB [8] sample nor with those present in previously reported experimental or computed diffractograms for CB [8] hydrate phases, 45 indicating that the CB molecules in CR@CB [8](100) adopt a different crystal packing arrangement. None of the PXRD patterns for the CR@CB[n] adducts display peaks assignable to a pure (bulk) CR phase, suggesting that the isolated solids are not physical mixtures of CB[n] and CR phases.…”

“…Characterisation data (FT-IR band frequencies, 1 C{ 1 H} CP MAS NMR chemical shifts) for CR and the protonated blue form of CR (PrCR, prepared as described in the ESI †) are given in the ESI. † The preparation and purification of CB [7] 44,45 ESI-MS studies ESI-MS spectra were obtained using a Bruker Daltonics HCT ultra mass spectrometer under positive and negative polarity. Sample solutions were prepared by dissolving CB[n] (n = 7 or 8) and CR in Milli-Q water to give a final concentration of 50 mM for each component.…”

Supramolecular Activation of S8 by Cucurbiturils in Water and Mechanism of Reduction to H2S by Thiols: Insights into Biological Sulfane Sulfur Trafficking

“…47 Based on the volume of S 8 (~149 Å 3 ), we expected that CB [7] (~279 Å 3 ) would be an ideal host for S 8 based on the calculated packing coefficient of 0.53 for CB [7]/S 8 . To test this hypothesis, we prepared the CB [6], CB [7], and CB [8] homologs using the Pellinger method, 48 and treated aqueous solution of each host in pH 7.4 PBS buffer with excess S 8 for 24 hours. After filtration of the heterogenous solutions, we measured the UV-Vis absorbance of each sample to determine whether S 8 ( max = 263 nm;  = 6730 M -1 cm -1 ) had been solubilized.…”