Chlorination of the C₁₀₀(18) fullerene with a mixture of VCl₄ and SbCl₅ gives rise to branched skeletal transformations affording non-classical (NC) C₉₄(NC1)Cl₂₂ with one heptagon in the carbon cage together with the previously reported C₉₆(NC3)Cl₂₀ with three heptagons. The three-step pathway to C₉₄(NC1)Cl₂₂ starts with two successive C₂ losses of 5:6 CC bonds to give two cage heptagons, whereas the third C₂ loss of the 5:5 CC bond from a pentalene fragment eliminates one of the heptagons. Quantum-chemical calculations demonstrate that the two unusual skeletal transformations—creation of a heptagon in C₉₆(NC3)Cl₂₀ through a Stone–Wales rearrangement and the presently reported elimination of a heptagon through C₂ loss—are both characterized by relatively low activation energy.

Catalytic isomerization of n-pentane was studied over novel high surface area (HS) aluminum fluoride supported palladium and platinum catalysts, prepared by the nonaqueous fluorolytic sol–gel synthesis. HS-AlF₃ maintained well its nanoscopic, mesoporous, and highly acidic character at higher temperatures, up to 350 °C. Both Pt/HS-AlF₃ and Pd/HS-AlF₃ catalysts, characterized by very small metal particle sizes (≈2 nm) maintained very good activity, stability, and selectivity towards isomerization (up to nearly 100 %) at up to 350 °C. Very strong acidity of HS-AlF₃ is the prerequisite for isomerization but the presence of the metal is also essential to maintain a high conversion level. The effect of metal–acid balance in Pd/HS-AlF₃ catalysts, important for bifunctional isomerization, was tested by screening three differently metal-loaded catalysts. The performance of the 0.5 wt % Pd/HS-AlF₃ appeared as good as that of 2.0 wt % Pd. The properties of the HS-AlF₃ support, catalyst precursors, and catalysts were characterized by XRD, TEM, H₂ chemisorption, and FTIR photoacustic spectroscopy of adsorbed pyridine, and NH₃ temperature programmed desorption. The first three methods allowed evaluating the state of the metal in the reduced catalysts. The suppressed chemisorption of H₂ must result from different factors, such as carbon presence in Pd introduced during catalyst synthesis and activation, metal–acidic support interaction, and, partially, metal encapsulation in AlF₃ during sol–gel synthesis. Lewis and Brønsted acidity was detected in activated catalysts and both types of acid sites were assumed to play a role in bifunctional isomerization. NH₃ effectively blocks the strongest acid sites and drastically limits the overall catalytic performance. Introduction of water to the reaction system also degrades, but to a lesser extent, the Pd(Pt)/HS-AlF₃ catalyst performance, most probably because of poisoning of only the strongest Lewis acid sites.

A one-pot synthesis of palladium nanoparticles supported on magnesium hydroxide fluoride has been performed with the fluorolytic sol–gel method. The prepared catalysts were characterized by using various physicochemical techniques. The sol–gel method led to high surface area (>135 m² g⁻¹), mesoporous catalysts (pore volume=0.19–0.23 cm³ g⁻¹, pore diameter=3–5 nm) with uniformly dispersed palladium nanoparticles approximately 2 nm in diameter on the surface. The catalysts synthesized by using different concentrations of aqueous hydrofluoric acid exhibited changing surface and acidic properties. Very high dispersion of palladium on magnesium fluoride (47 %) was obtained with 1 wt % palladium loading. The catalysts were used for hydrogenation of various olefins in the presence of other organic functionalities at room temperature and atmospheric hydrogen pressure. Various substituted olefins were hydrogenated with almost 100 % conversion and selectivity. The catalysts were recycled efficiently over five cycles without appreciable loss in catalytic activity. There was no palladium leaching under the reaction conditions, which was confirmed by inductively coupled plasma atomic emission spectroscopy analysis. Activation of olefin on the catalyst surface could not be observed by in situ FTIR studies, indicating facile activation of hydrogen on the palladium supported on magnesium hydroxide fluoride.

Chlorination of C₁₀₀ fullerene with a mixture of VCl₄ and SbCl₅ afforded C₉₆Cl₂₀ with a strongly unconventional structure. In contrast to the classical fullerenes containing only hexagonal and pentagonal rings, the C₉₆ cage contains three heptagonal rings and, therefore, should be classified as a fullerene with a nonclassical cage (NCC). There are several types of pentagon fusions in the C₉₆ cage including pentagon pairs and pentagon triples. The three-step pathway from isolated-pentagon-rule (IPR) C₁₀₀ to C₉₆(NCC-3hp) includes two C₂ losses, which create two cage heptagons, and one Stone–Wales rotation under formation of the third heptagon. Structural reconstruction established C₁₀₀ isomer no. 18 from 450 topologically possible IPR isomers as the starting C₁₀₀ fullerene. Until now, no pristine C₁₀₀ isomers have been confirmed based on the experimental results.

Nanoscopic metal fluorides with surface hydroxy groups are of broad interest in heterogeneous catalysis. With both Lewis and Brønsted acid sites on the surface, these catalysts can be applied to a wide range of reactions. Having previously synthesised AlF₃- and MgF₂-based catalysts, we report a new transition metal fluoride with bi-acidity. A pre-dehydration procedure was developed to introduce hydroxy groups to a Lewis acid, FeF₃. Subsequently, ternary nanoscopic FeF₃-MgF₂ with enhanced porosity was prepared through a one-step fluorination. The interaction between MgF₂ and FeF₃ was elucidated. Surface characterisation revealed a remarkable increase in the surface area of FeF₃-MgF₂ compared with FeF₃. More importantly, medium–strong Lewis and Brønsted acid sites were detected on the FeF₃-MgF₂ surface. In line with its bi-acidity, FeF₃-MgF₂ was highly active in the model reaction, the isomerisation of citronellal to isopulegol. Finally, we discuss how the porosity and surface acidity jointly determine the activity of FeF₃-MgF₂. Our study demonstrates the feasibility of ternary FeF₃-MgF₂ and opens new possibilities to synthesise bi-acidic fluoride catalysts.

Trifluoromethylation of a higher fullerene mixture with CF₃I was performed in ampoules at 550 °C. HPLC separation followed by crystal growth and X-ray diffraction study resulted in the structure elucidation of nine CF₃ derivatives of D_2d-C₈₄ (isomer 23). The molecular structures of C₈₄(23)(CF₃)₄, C₈₄(23)(CF₃)₈, C₈₄(23)(CF₃)₁₀, C₈₄(23)(CF₃)₁₂, two isomers of C₈₄(23)(CF₃)₁₄, two isomers of C₈₄(23)(CF₃)₁₆, and C₈₄(23)(CF₃)₁₈ were discussed in terms of their addition patterns and the relative formation energies. Extensive theoretical DFT calculations were performed to identify the most stable molecular structures. It was found that the addition of CF₃ groups to the C₈₄(23) fullerene is governed by two main rules: no additions in positions of triple hexagon junctions and predominantly para additions in C₆(CF₃)₂ hexagons on the fullerene cage. The only exception with an isolated CF₃ group in C₈₄(23)(CF₃)₁₂ is discussed in more detail.

Trifluoromethylation of higher fullerene mixtures with CF₃I was performed in ampoules at 400 to 420 and 550 to 560 °C. HPLC separation followed by crystal growth and X-ray diffraction studies allowed the structure elucidation of nine CF₃ derivatives of D₂-C₈₄ (isomer 22). Molecular structures of two isomers of C₈₄(22)(CF₃)₁₂, two isomers of C₈₄(22)(CF₃)₁₄, four isomers of C₈₄(22)(CF₃)₁₆, and one isomer of C₈₄(22)(CF₃)₂₀ were discussed in terms of their addition patterns and relative formation energies. DFT calculations were also used to predict the most stable molecular structures of lower CF₃ derivatives, C₈₄(22)(CF₃)_2–10. It was found that the addition of CF₃ groups to C₈₄(22) is governed by two rules: additions can only occur at para positions of C₆(CF₃)₂ hexagons and no additions can occur at triple-hexagon-junction positions on the fullerene cage.

Vitamin K₄ (menadiol diacetate, MDD) can be easily synthesized through cleaner and more efficient catalytic alternatives following the green chemistry principles. Ionic gold-based hydroxylated fluorides are active bi-functional catalysts for the one-pot hydroacetylation of menadione leading to MDD with 77% selectivity. Unprecedent results were obtained in the presence of oxide-fluoride catalysts by using a microwave-assisted hydrogen-transfer (Meerwein–Ponndorf–Verley reaction) coupled with an acetylation approach, yielding very high selectivities for the target product (95%).

Fluorolytic sol–gel synthesis with aqueous HF results in highly disordered, nanoscopic magnesium hydroxide fluorides with very large BET surface areas, low carbon contents, and adjustable stoichiometries. MgF_x(OH)_(2–x) materials that can withstand high temperatures can be synthesized in a very wide stoichiometric range by fluorolytic sol–gel synthesis (0 ≤ x ≤ 2). Large surface areas and a very wide range of tunable acid–base properties are characteristic for these compounds, which opens an exciting possibility of their application not only as new catalysts but also as support materials.

In this paper, recent developments in the field of catalysts based on nanosized metal fluorides are presented with special focus on the exciting and promising magnesium fluoride systems. The majority of these new catalyst systems originate from the work of the authors based on the fluorolytic sol–gel synthesis of metal fluorides, which was developed by this group. They are selected in a way as to highlight the principles and prospects of this new approach to high-surface-area, strongly distorted metal fluorides. This new fluorolytic sol–gel route to metal fluorides opens, in the opinion of the authors, a very broad range of scientific and technical applications of the accessible high-surface-area metal fluorides. By combining fluorolytic and hydrolytic sol–gel synthesis, this approach can be further extended, also providing access to metal hydroxide fluorides or metal oxide fluorides. The different synthesis strategies as well as the catalytic applications of various MgF₂-based materials are described in detail in this review.

The partly hydroxylated MgF₂ and AlF₃ materials are efficient and selective catalysts for the preparation of two important members of the vitamin K class: vitamin K₁ and vitamin K₁-chromanol. The high activity in combination with high selectivity in one of the target products is due to both the acidic strength and the synergistic effect of the presence of both, optimized Brønsted and Lewis sites. Therefore, the best catalyst for a target product can be obtained through a very simple tuning of the acidic properties of the material. Moreover, the results obtained in the present study (Y_vitamin K1=57.8 % and Y_{vitamin K1-chromanol}=71.4 %) are also very encouraging from the environmental standpoint as green elements are introduced by using solid catalysts and a biphasic solvent system.

In the search for intermediates during the sol–gel synthesis of nanoscopic AlF₃, the fluorolysis of aluminum isopropoxide by HF in pyridine has been investigated. By varying the Al to HF ratio from 0.5 to 2, three aluminum alkoxide fluorides, Al₃F(Py)(OiPr)₈, Al₇F₁₀(μ₄-O)(OiPr)₉(Py)₃·1.34Py, and Al₁₀F₁₆(μ₄-O)₂(OiPr)₁₀(Py)₄·4.17Py, were isolated and structurally characterized. The structures of these compounds are discussed as possible snapshots in the consecutive fluorolytic sol–gel formation of nanoscopic AlF₃ and give deeper insight into the probable reaction pathway. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The high thermal and chemical stability of C_3v-C₆₀(CF₃)₁₈ allowed its isolation from a complex C₆₀(CF₃)_n isomer mixture followed by characterization with ¹⁹F NMR spectroscopy and single-crystal X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A novel nanoscopic, partly hydroxylated aluminium fluoride was prepared in a sol-gel fluorination synthesis and characterised by IR probe molecules. It was shown that this material has, in contrast to high surface area aluminium fluoride (HS-AlF₃) which is one of the strongest Lewis acids, a low amount of strong Lewis acid sites combined with weak and medium strength Brønsted sites. Both materials were tested in the synthesis of (all-rac)-α-tocopherol through the condensation of 2,3,6-trimethylhydroquinone (TMHQ) with isophytol (IP). The activity data indicate the partly hydroxylated aluminium fluoride to be a very efficient and highly selective catalyst for (all-rac)-α-tocopherol (>99.9%, for an IP conversion of 100%) whereas high surface area aluminium fluoride is a poor catalyst for this reaction.

The first four isomers of C₇₀(n-C₃F₇)₈ synthesized by the ampoule reaction of C₇₀ with n-C₃F₇I, isolated by HPLC, and characterized by X-ray crystallography possess unprecedented addition patterns among C₇₀X₈ compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A non-aqueous sol–gel Al-based fluoride has been subjected to the microwave solvothermal process. The final material depends on the temperature heat treatment used. Three types of material have been prepared: 1) for low temperature heat treatment (90 °C) X-ray amorphous alkoxy fluoride was obtained; 2) for the highest temperature used (200 °C) the metastable form β-AlF₃ was obtained with a very large surface area of 125 m² g⁻¹. The mechanism of the amorphous⇄crystalline transformation has been rationalised by the occurrence of a decomposition reaction of the gel fluoride induced by the microwave irradiation. 3) Finally, at intermediate temperature (180 °C) a multi-component material mixture exhibiting a huge surface area of 525 m² g⁻¹ has been obtained and further investigated after mild post-treatment fluorination using F₂ gas. The resulting aluminium-based fluoride still possesses a high-surface-area of 330 m² g⁻¹. HRTEM revealed that the solid is built from large particles (50 nm) identified as α-AlF₃, and small ones (10 nm), relative to an unidentified phase. This new high-surface-area material exhibits strong Lewis acidity as revealed by pyridine adsorption and catalytic tests. By comparison with other materials, it has been shown that whatever the composition/structure of the Al-based fluoride materials, the number of strong Lewis acid sites is related to the surface area, highlighting the role of surface reconstruction occurring on a nanoscopic scale on the formation of the strongest Lewis acid sites.

Novel magnesium fluorides have been prepared by a new fluorolytic sol–gel synthesis for fluoride materials based on aqueous HF. By changing the amount of water at constant stoichiometric amount of HF, it is possible to tune the surface acidity of the resulting partly hydroxylated magnesium fluorides. These materials possess medium-strength Lewis acid sites and, by increasing the amount of water, Brønsted acid sites as well. Magnesium hydroxyl groups normally have a basic nature and only with this new synthetic route is it possible to create Brønsted acidic magnesium hydroxyl groups. XRD, MAS NMR, TEM, thermal analysis, and elemental analysis have been applied to study the structure, composition, and thermal behaviour of the bulk materials. XPS measurements, FTIR with probe molecules, and the determination of N₂/Ar adsorption–desorption isotherms have been carried out to investigate the surface properties. Furthermore, activity data have indicated that the tuning of the acidic properties makes these materials versatile catalysts for different classes of reactions, such as the synthesis of (all-rac)-[α]-tocopherol through the condensation of 2,3,6-trimethylhydroquinone (TMHQ) with isophytol (IP).