Theoretical investigation on bond and spectrum of cyclo[18] carbon (C) with sp-hybridized.

In an experiment, cyclo[18]carbon (C), prepared with low-temperature STM-AFM (scanning tunneling microscopy-atomic force microscopy) from CO, CO, and CO molecules, have been confirmed being alternating single and triple bonds structure. Nevertheless, the stability of C is weak at room temperature in gas. Thus, it is difficult to study the spectrum, orbital, and bonds characters of the C molecule in the experiment. In this paper, we have obtained absorption spectrum, orbital, and bonding characters of the C molecule in theory. Besides, bonds and spectra of CO, CO, CO, BN, C, C, C, and C molecules have been investigated to further confirm the structure and the characters of the C molecule. The results show that carbon-carbon bonds of CO, CO, and CO molecules in ring are alternating single and triple bonds except those connected with CO group. BN molecule as the isoelectronic structure of C has a larger bandgap and shorter wavelength of absorption spectra than those of the C molecule. Moreover, all bonds between boron and nitrogen in BN molecule are single one. Study bonding characters for C, C, C, and C molecules have confirmed that carbon-carbon bonds of cyclo[n]carbon changed gradually from double bonds to alternating single and triple bonds with increasing n value. The data from theory would give help for future research on C and BN molecules in experiment. Graphical abstract Theoretical investigation for bond and spectra characters of cyclo[18]carbon (C), prepared with low-temperature STM-AFM (scanning tunneling microscopy-atomic force microscopy) from CO, CO, and CO molecules, which have been confirmed being alternating single and triple bonds structure.