Two Modifications Formed by “Sulflower” C₁₆S₈Molecules, Their Study by XRD and Optical Spectroscopy (Raman, IR, UV−Vis) Methods

Abstract

Sublimation of sulflower, octathio[8]circulene C 16S 8 ( 1), on heating under high vacuum ( approximately 10 (-5) Torr) leads to successive formation of two modifications: a white film ( 1W) and a red polycrystalline solid ( 1R). When kept at room temperature for several weeks, 1W spontaneously turns pink, reflecting the monotropic phase transition 1W --> 1R. The accurate molecular and crystal structure of 1R has been studied using low-temperature (100 K) high-resolution single crystal X-ray analysis. The C 16S 8 molecule in crystal is strictly planar with nearly equalized bonds of each type (C-C, C-S, and CC). The point symmetry group of the free molecule is D 8 h , and the crystal space group is P2 1/ n. These data allowed group-theoretical analysis of vibrational normal modes to be accomplished. Investigation of the charge density distribution of 1R including Bader's AIM approach has revealed rather strong intermolecular S...S, S...C, and C...C interactions of charge transfer and pi-stacking types with overall lattice energy of 28.5 kcal/mol. The charge transfer due to the S...S interactions is the reason for the red coloration of 1R. The latter is reflected by its UV-vis spectrum exhibiting absorption bands in the visible region which are absent from that of 1W. Both modifications were studied comparatively by vibrational (Raman, IR) and electronic spectroscopies as well as XRD powder diffraction. All the results obtained are fully consistent and show that 1W is much less ordered than 1R with significantly weakened intermolecular interactions. Rationalizing of these results has led to an idea that 1W could be soluble, in contrast to 1R. Indeed, 1W appeared soluble in common solvents; this finding opens the way to the study of the chemistry of 1 and investigation of its electrooptical properties.

Electronic structure, aromaticity and spectra of hetero[8]circulenes

“…21,52,53 sym-Tetraselenatetrathia [8]circulene 10 prepared two years later has a similar planar structure. 22,28 Azaoxa [8]circulenes 23,24 prepared by the group of Pittelkow are the latest synthesized heterocirculenes.…”

“…It is interesting that the vacuum sublimation of OTC affords two phases of white and red colour. 52 The white film corresponds to the amorphous state of OTC with the chaotic arrangement of the molecules, whereas the red film consists of single-crystalline OTC having the strictly ordered crystal structure. Evidently, different colours of these phases are associated with the different structural organization of amorphous and crystalline sulflower.…”

Oligômeros e polímeros derivados do tiofeno: síntese e aplicações

“…64 Além disso, tem-se obtido oligômeros macrocíclicos π-conjugados de tiofenos (23) 65 que, devido ao seu alto grau de conjugação, poderão ser aplicados em dispositivos eletrônicos orgânicos, como ressaltam os autores.…”

Electrochemical field-effect transistors of octathio[8]circulene robust thin films with ionic liquids

“…Octathio [8]circulene (1), called 'sulflower' (see Fig. 1), is a newcomer in this materials family [4][5][6]. It is attracting much attention from various viewpoints, such as the molecular symmetry caused by anti-aromaticity with the 8p electrons on the inner ring and orbital degeneracy, and the intermolecular packing caused by the sulfur atoms exposed to the outside of the molecular rings [7][8][9].…”

“…It is attracting much attention from various viewpoints, such as the molecular symmetry caused by anti-aromaticity with the 8p electrons on the inner ring and orbital degeneracy, and the intermolecular packing caused by the sulfur atoms exposed to the outside of the molecular rings [7][8][9]. This compound is a promising material in organic electronics, because of a characteristic 3D close packing in the crystal [6,10] (see Fig. 1) and chemical stability.…”