[6]Cyclo-2,7-naphthylene: a redetermination

Single crystals of a macrocyclic hydrocarbon, [6]cyclo-2,7-naphthylene ([6]CNAP, C60H36) were prepared from anthracene melt with a prolonged time for the recrystallization. The crystal of improved quality led to the correction of the space-group assignment to Cmca from in the original determination [Nakanishi et al. (2011 ▶) Angew. Chem. Int. Ed. 50, 5323–5326] and the refinement of anisotropic displacement parameters of all C atoms. The refined molecular structure with C 2h point symmetry indicated that the strain on the naphthyl rings of [6]CNAP is smallest among the congeners. Despite the large macrocyclic structure, molecules are packed in a ubiquitous herringbone motif. A short C—C distance of 3.119 (4) Å was found in the stacking direction, and a short C—H distance of 2.80 Å was found in the intercolumnar contact.

Single crystals of a macrocyclic hydrocarbon, [6]cyclo-2,7naphthylene ([6]CNAP, C 60 H 36 ) were prepared from anthracene melt with a prolonged time for the recrystallization. The crystal of improved quality led to the correction of the spacegroup assignment to Cmca from P1 in the original determination [Nakanishi et al. (2011) Angew. Chem. Int. Ed. 50, 5323-5326] and the refinement of anisotropic displacement parameters of all C atoms. The refined molecular structure with C 2h point symmetry indicated that the strain on the naphthyl rings of [6]CNAP is smallest among the congeners. Despite the large macrocyclic structure, molecules are packed in a ubiquitous herringbone motif. A short C-C distance of 3.119 (4) Å was found in the stacking direction, and a short C-H distance of 2.80 Å was found in the intercolumnar contact.

Related literature
Superior quality crystals of the title compound were obtained by re-optimizing the crystallization conditions. For the synthesis and preceding crystallographic analysis, see: Nakanishi et al. (2011). For the original method of recrystallization, see: Miyahara & Shimizu (2001). For a review of C-HÁ Á Á contacts in crystals, see: Nishio (2004 Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 and Yadokari-XG 2009 (Kabuto et al., 2009) and publCIF (Westrip, 2010 Nakanishi et al., 2011). The unique macrocyclic structures of [n]CNAPs (n = 5, 6 and 7) were revealed by X-ray crystallographic analysis of the single crystals, but we deferred detailed discussion of the most abundant compounds, [6]CNAP, because of insufficient quality of available data mainly due to weak reflections from the previous crystals. We now obtained single crystals of [6]CNAP with superior quality by re-optimizing the crystallization conditions and successfully corrected the space group assignment to Cmca. The molecular structure of title compound is shown in Fig. 1, and the packing structure is shown in Fig. 2. Most importantly, the refined molecular structure with C 2h point symmetry shows that [6]CNAP has the smallest deformation in the planar naphthyl rings with the average bend angle of 2.3° which is smaller than 16° and 5° of [5]-and [7]CNAPs, respectively. To form the strain-free macrocycle, the naphthyl rings are twisted alternately with dihedral angles of 33.1 (3)° and 25.6 (4)°. Despite the large macrocyclic structure, molecules are packed in a ubiquitous herringbone motif. A short C-C distance of 3.119 (4) Å was found in the stacking direction, and a short C-H distance of 2.80 Å was found in the intercolumnar contact.

Experimental
The title compound was synthesized by a nickel promoted coupling reaction of 2,7-dibromonaphthalene and separated as reported in literature (Nakanishi et al., 2011). A single crystal suitable for X-ray crystallographic analysis was obtained by a solid solvent growth method, as reported except that the time for crystal growth was extended: A mixture of anthracene (200 mg) and [6]CNAP (4 mg) was sealed in a glass tube. The whole glass tube was heated at 350 °C for 2 h. The subsequent crystal-growing time at 210 °C was extended from 2 h to 3 h, and the tube was cooled gradually to ambient temperature.
A half of the glass tube was then heated at 200 °C to eliminate anthracene and afford crystals of [6]CNAP. For the original method of recrystallization, see: Miyahara & Shimizu (2001).

Refinement
H atoms were included in calculated positions and treated as riding atoms, with C-H = 0.95 Å (aromatic) and U iso (H) = 1.2U eq (C).
[6]Cyclo-2,7-naphthylene as those based on F, and R-factors based on ALL data will be even larger.