title: DFT study of zigzag (n, 0) single-walled carbon nanotubes: (13)C NMR chemical shifts.
abstract: (13)C NMR chemical shifts of selected finite-size models of pristine zigzag single walled carbon nanotubes (SWCNTs) with a diameter of ∼0.4-0.8nm and length up to 2.2nm were studied theoretically. Results for finite SWCNTs models containing 1, 4 and 10 adjacent bamboo-type units were compared with data obtained for infinite tubes in order to estimate the reliability of small finite models in predicting magnetic properties of real-size nanotubes and to assess their tube-length dependence. SWCNTs were fully optimized using unrestricted density functional theory (DFT-UB3LYP/6-31G*). Cyclacenes, as the shortest models of open-ended zigzag SWCNTs, with systematically varying diameter were calculated as well. GIAO NMR calculations on the SWCNT and cyclacene models were performed using the BHandH density functional combined with relatively small STO-3Gmag basis set, developed by Leszczyński and coworkers for accurate description of magnetic properties. Regular changes of carbon (13)C chemical shifts along the tube axis of real size (6, 0) and (9, 0) zigzag carbon nanotubes were shown. The (13)C NMR shifts according to increasing diameter calculated for zigzag (n, 0, n=5-10) cyclacenes followed the trends observed for zigzag (n, 0) SWCNTs. The results for 4-units long SWCNTs match reasonably well with the data obtained for infinite zigzag (n, 0) SWCNTs, especially to those with bigger diameter (n=8-15). The presence of rim hydrogens obviously affects theoretical (13)C chemical shieldings and shifts in cyclacenes and thus cyclacenes can provide only approximate estimation of (13)C NMR parameters of real-size SWCNTs. The NMR properties predicted for the longest 10-units long models of SWCNTs reliably correspond to results obtained for infinite nanotubes. They were thus able to accurately predict also recently reported experimental chemical shift of chiral (6, 5) SWCNT.
authors.affiliation: University of Opole, Faculty of Chemistry, 48, Oleska Street, 45-052 Opole, Poland. Electronic address: teobaldk@gmail.com.
authors.forename: Teobald
authors.initials: T
authors.lastname: Kupka
authors.affiliation: University of Opole, Faculty of Chemistry, 48, Oleska Street, 45-052 Opole, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Stachów
authors.affiliation: Faculty of Chemical and Process Engineering, Warsaw University of Technology, Waryńskiego 1, 00-645 Warsaw, Poland.
authors.forename: Leszek
authors.initials: L
authors.lastname: Stobiński
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, 166 10 Prague, Czech Republic. Electronic address: kaminsky@uochb.cas.cz.
authors.forename: Jakub
authors.initials: J
authors.lastname: Kaminský
mesh_terms: D066241:Carbon-13 Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D037742:Nanotubes, Carbon / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D037742:Nanotubes, Carbon
keywords: Cyclacenes; DFT; NMR; Theoretical modeling; Zigzag SWCNT