Vibrational spectrum ofC60sin the p-tert-butylcalix[8]arene(1:1)C60

Abstract

We report the results of Raman, infrared, and inelastic neutron scattering investigations of the vibrational spectrum of the complex p-tert-butylcalix͓8͔arene͑1:1͒fullerene, a system with almost isolated C 60 molecules confined inside neutral cages. All the internal optical-active modes of the C 60 guest have been identified, and further modes which can be attributed to C 60 intramolecular vibrations appear in the neutron scattering function. A comparison with the vibrational spectrum of empty p-tert-butylcalix͓8͔arene indicates that the hostguest interaction is very weak. As solid-state effects are also practically suppressed, the investigated complex gives the unique opportunity to study almost free fullerene balls confined in the solid state.A huge number of theoretical and experimental studies followed the discovery of the new fullerene allotropes of carbon. Much of the interest has been focused on the dynamical properties of C 60 , and a comprehensive picture of the vibrational behavior has been obtained by a combination of neutron, Raman, and infrared scattering experiments. 1-6 However, it is not yet clear to what extent the presence of solid-state effects complicates the comparison of the experimental results with quantum-mechanical calculations performed for isolated C 60 molecules. The splitting of the degenerate molecular modes deserves further investigation as well, being not only a consequence of the crystal field, 6 but also the result of 12 C/ 13 C isotopic effects 7 and of merohedral orientational disorder in crystalline C 60 . 8 Here we present light and neutron spectroscopy results which reveal the existence of a unique opportunity of studying the behavior of fullerene in a quasifree environment. Actually, the experimental findings show that the C 60 molecules, confined in the solid-state complex with p-tert-butylcalix͓8͔arene, are almost isolated.Calixarenes are cup-shaped macrocyclic phenolic oligomers which find increasing applications as building blocks of receptors for the selective complexation of alkali and alkaline-based metal cations. Moreover, for their ability to form inclusion complexes with neutral organic molecules, calixarenes have been the subject of a number of investigations in the framework of the host-guest or supramolecular chemistry. 9 Among this class of synthetic matrices, the p-tert-butylcalix͓n͔arene ͑where nϭ8 refers to the number of phenolic units͒, is able to include the fullerene molecule, and recently a ͑1:1͒ complex of p-tert-butylcalix͓8͔arene with C 60 has been obtained. 10,11 This is an important breakthrough in fullerene chemistry, offering an economic means of C 60 purification and providing, on the other hand, an interesting inclusion system for the study of the C 60 dynamics. Actually, infrared ͑IR͒, visible, and ultraviolet spectra, together with 13 C NMR results, strongly indicate that the C 60 is weakly bound to the upper edge of the calix͓8͔arene cavity ͑Fig. 1͒ and that interactions among the fullerene molecules PHYSICAL

Structural and electronic properties of organo-halide lead perovskites: a combined IR-spectroscopy and ab initio molecular dynamics investigation

“…Broadening of the IR bands is associated with the fast rotational motion of MA cations, as observed in other systems where molecules are free to rotate in the solid state like plastic crystals of C 60 . 41 Most notably, our simulations also reproduce the experimental red-shift of this band with the temperature (see Fig. 4c).…”

GIAO-DFT calculated and experimentally derived complexation-induced chemical shifts of calix[4]arene–solvent inclusion complexesElectronic supplementary information (ESI) available: calculated and observed NMR data and geometrical details for complexes 1–3, 1–4 and 1–5. See http://www.rsc.org/suppdata/p2/b1/b110078p/

“…However, this methodology strongly depends on the accessibility of single-crystalline material. In cases where such crystalline material is not available, 13 C CP-MAS NMR, 7-16 vibrational spectroscopy, [17][18][19][20][21][22][23][24] or thermochemical methods 25-28 are applicable. In solution, NMR titration experiments have found widespread use for the characterisation of inclusion processes.…”

Efficient Synthesis, Structure, and Complexation Studies of Electron‐Donating Thiacalix[n]dithienothiophene

“…The Raman and FTIR spectra do not exhibit obvious differences between the crystal and free C 60 . [14] Since the crystal has an S 4 axis in the center of the macrocycle, the cavities are crystallographically identical, which gives rise to the "Janus-head" in 2 a. Although there are several examples of 1:2 the macrocycle-C 60 complex, the number of 1:2-complex crystal structures with highly symmetrical orientations is small.…”