Augmentation of the life time of cyclo[18]carbon accustomed with carbon nanotube and zeolite Wahida Rahaman,† and Arijit Bag∗,‡ Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, 741246,West Bengal, India., and Department of Applied Sciences, Maulana Abul Kalam Azad University of Technology, Simhat, Haringhata, 741249, West Bengal, India E-mail: [email protected] Recently synthesized cyclo[18]carbon which is characterized as polyyne D9h has a very short lifetime even at 5 K temperature. Its au- tomerization is proposed through a transition state which is reported as a D18h symmetric cumulene. In the present article, an experi- mentally viable method for the enhancement of the lifetime of this compound is reported. The carbon nanotube is employed for this pur- pose. We also report that adopting numerous molecules of cyclo[18]carbon in the womb of a zeolite cage, wire-like countenance construc- tion is feasible. ∗To whom correspondence should be addressed †Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, 741246,West Bengal, India. ‡Department of Applied Sciences, Maulana Abul Kalam Azad University of Technology, Simhat, Haringhata, 741249, West Bengal, India 1 Cyclo[18]carbon is the 1st sp-hybridized carbon allotrope which is synthesized by Kaiser et. al.1 and then characterized by several research groups.2–4 Though, pro tempore, its application in material science or in any other field of research is not translucent. Of course, there is monstrous prospect of its impersonation, in assorted areas of material science, synthetic chemistry and energy materials.4–7 It is lamentable that presently synthesized cyclo[18]carbon which is formulated on bilayer NaCl on Cu(111) at 5 K temperature by using atom manipulation technique, has a very short lifetime. But, for its fecund embodiment in versed technology, we have to synthesize it in such a fashion that it should subsist for usable finite time. To reach this destination, we embed it with carbon nanotube (CNT) and zeolite. Cyclo[18]carbon was first predicted by Hoffmann in 19668 which was pursued by appreciable theoretical and experimental studies.1,9–20 The density functional theory (DFT),17 Møller-Plesset perturbation theory (MP)18 computation reported that the lowest energy state of cyclo[18]carbon 2 is of cumulenic D18h symmetry where all carbon atoms are sp hybridized and all carbon-carbon bonds are the double bonds. Contrary to this, the ground state optimized geometry of cyclo[18]carbon at the Hartree-Fock11 and Coupled Cluster (CC)12 level of theory prognosticate the presence of all sp hybridized carbon which are attired in an alternative single and triple carbon-carbon bonds. A high-level Monte Carlo computation19 endorses the upshot of the Hartree-Fock and CC results ie. a 1 ployyne D9h symmetric structure of cyclo[18]carbon which is equiponderant with the experiment. Subsequent theoretical exploration by Nandi et. al.4 after the experimental synthesis of cy- clo[18]carbon, point out that though the ground state symmetry is D9h, it should experience an 4 automerization between two respective geometries through a cumulenic D18h state. Nandi et. al. denominated this state as a "Transition State". A similar conclusion is made by Glib et. al.3 also. But, we expostulate this presumption because a true transition state should have only one imagi- nary mode of vibration along with the bond breaking or bond making. Thus, there would not be cumulenic D18h symmetry. Contrariwise, DFT and MP computation substantiated that the cumu- lenic D18h symmetric state of cyclo[18]carbon is an optimized state on the potential energy surface 17,18 with all positive modes of vibration. Henceforth, we may conclude that the cumulenic D18h 2 symmetric state is the geometric excited state of cyclo[18]carbon. According to Nandi et. al., this excitation energy is 9.6 kcal/mol. This energy barrier is quite high enough as the experiment is performed at 5 K. Thus, automerization would be practically possible through quantum tunneling only which is smeared in the reported article by Nandi et. al. In the present research, it is observed that the single carbon-carbon bond is shorter than normal C−C bond while carbon-carbon triple bond is nearly the same as an ideal C≡C. The extra stabi- lization energy of strung cyclo[18]carbon inside the chosen CNT is -1.05 kcal/mol. Thus, if the synthesis is steered in an apposite CNT, it is prospective that the lifetime of cyclo[18]carbon would be prolonged. Unfortunately, the imposition of cyclo[18]carbon in the womb of an alpha cage of zeolite-Y destabilizes it. Though, the destabilization energy is minimal, 0.14 kcal/mol. But, it is possible to make a wire-like countenance with two untrammeled cyclo[18]carbons at the interior of the excavation of zeolite cage recherche in this perusal. The optimized geometry is presented in Figure 1 (a). Conversely, analogous wire-like gestalt is not possible for CNT (see Figure 1 (b)). It may be due to the lack of a strong confinement effect. (a) (b) Figure 1: Optimized geometry of two untrammeled cyclo[18]carbons (a) inside the alpha cage of zeolite-Y (b) inside CNT. Single-layer of CNT (truncation is done with hydrogen atom) with different core sizes (carbon numbers are 32, 36 and 40 respectively) are chosen for our study. Hartree-Fock level calculations are accomplished with Gaussian 0921 program package. It is observed that the CNT of 40 carbon atom is capable of appropriate stabilization. Both CNT and cyclo[18]carbon ring are co-centric, 3 though, there is an angle between their molecular planes. The optimized geometry of this system is presented in Figure 2. For smaller cavity CNT, cyclo[18]carbon ring moves to the outside of CNT. Figure 2: Optimized geometry of cyclo[18]carbons inside CNT. The stability computation of cyclo[18]carbon within the alpha cage of zeolite-Y is performed with 6-31G basis employing Gaussian 09 at the Hartree-Fock level. Here, the crystal structure of zeolite-Y is taken from the crystallographic database which is kept unchanged during the optimiza- tion process. As mentioned before, wire formation with cyclo[18]carbons is possible when it is placed amidst the zeolite core. This annotation should enlighten the infliction of cyclo[18]carbon in future technology. Present work of molecular engineering of cyclo[18]carbon with CNT and zeolite as the host is lucrative and prudential. This contrivance for augmentation of the lifetime of cyclo[18]carbon may foster diversified researchers in various fields of theory and experiment. Wahida Rahaman acknowledges the financial support from IISER Kolkata, India. A. Bag ac- knowledges the central computational facilities of IISER Kolkata. References (1) Kaiser, K.; Scriven, L. M.; Schulz, F.; Gawel, P.; Gross, L.; Anderson, H. L. “An sp- hybridized molecular carbon allotrope, cyclo [18] carbon”, Science 2019, 365, 1299–1301. (2) Castelvecchi, D. “Chemists make first-ever ring of pure carbon.”, Nature 2019, 572, 426. 4 (3) Baryshnikov, G. V.; Valiev, R. R.; Kuklin, A. V.; Sundholm, D.; Agren, H. “Cyclo [18] Carbon: Insight into Electronic Structure, Aromaticity and Surface Coupling”, The journal of physical chemistry letters 2019, 10, 6701–6705. (4) Kozuch, S.; Nandi, A.; Solel, E. “Carbon Tunneling in the Automerization of Cyclo [18] Carbon”, Chemistry–A European Journal 2019, . (5) Yuan, Y.; Lu, J. “Demanding energy from carbon”, Carbon Energy 2019, . (6) Pichierri, F. “Boron-nitrogen analogues of cyclo [18] carbon”, Chemical Physics Letters 2020, 738, 136860. (7) Celaya, C. A.; Salcedo, R.; Sansores, L. E. “Molecular knot with nine crossings: Structure and electronic properties from density functional theory computation”, Journal of Molecular Graphics and Modelling 2019, 107481. (8) Hoffmann, R. “Extended hückel theoryâA˘Tv:ˇ Cumulenes, polyenes, polyacetylenes and cn”, Tetrahedron 1966, 22, 521–538. (9) Beezer, A.; Mortimer, C.; Springall, H.; Sondheimer, F.; Wolovsky, R. “The heat of combus- tion of cyclo-octadecanonaene ([18] annulene)”, Journal of the Chemical Society (Resumed) 1965, 216–220. (10) Jasti, R.; Bhattacharjee, J.; Neaton, J. B.; Bertozzi, C. R. “Synthesis, characterization, and theory of [9]-,[12]-, and [18] cycloparaphenylene: carbon nanohoop structures”, Journal of the American Chemical Society 2008, 130, 17646–17647. (11) Parasuk, V.; Almlof, J.; Feyereisen, M. W. “The [18] all-carbon molecule: cumulene or polyacetylene?”, Journal of the American Chemical Society 1991, 113, 1049–1050. (12) Arulmozhiraja, S.; Ohno, T. “CCSD calculations on C 14, C 18, and C 22 carbon clusters”, The Journal of chemical physics 2008, 128, 114301. 5 (13) Diederich, F.; Rubin, Y.; Knobler, C. B.; Whetten, R. L.; Schriver, K. E.; Houk, K. N.; Li, Y. “All-carbon molecules: evidence for the generation of cyclo [18] carbon from a stable organic precursor”, Science 1989, 245, 1088–1090. (14) Diederich, F.; Kivala, M. “All-carbon scaffolds by rational design”, Advanced materials 2010, 22, 803–812. (15) McElvany, S. W.; Ross, M. M.; Goroff, N. S.; Diederich, F. “Cyclocarbon coalescence: Mechanisms for tailor-made fullerene formation”, Science 1993, 259, 1594–1596. (16) Diederich, F. “Carbon scaffolding: building acetylenic all-carbon and carbon-rich com- pounds”, Nature 1994, 369, 199. (17) Saito, M.; Okamoto, Y. “Second-order Jahn-Teller effect on carbon 4 N+ 2 member ring clusters”, Physical Review B 1999, 60, 8939. (18) Martin, J. M.; El-Yazal, J.; François, J.-P. “Structure and vibrational spectra of carbon clus- ters Cn (n= 2–10, 12, 14, 16, 18) using density functional theory including exact exchange contributions”, Chemical physics letters 1995, 242, 570–579. (19) Torelli, T.; Mitas, L. “Electron correlation in C 4 n+ 2 carbon rings: aromatic versus dimer- ized structures”, Physical review letters 2000, 85, 1702.