(E)-7-(Pyren-1-yl)hept-6-enoic acid

The title compound, C23H20O2, is a precursor of a pyrene-based supramolecular element for non-covalent attachment to a carbon nanotube. The asymmetric unit contains three independent molecules. The carboxylic acid group in each of these molecules serves as an intermolecular hydrogen-bond donor and acceptor, generating the commonly observed double O—H⋯O hydrogen-bond motif in an eight-membered ring. Weaker C—H⋯O, π–π [centroid–centroid distance = 3.968 (4) Å] and C—H⋯π interactions are also found in the crystal structure.

side chain. Similar to that trienoic acid (Bariamis, et al., 2009) the carboxyl groups of three molecules of the title compound are connected to carboxyl group of another molecule with double hydrogen bonding interactions (Table 1), generating the R 2 2 (8) graph-set motif (Bernstein et al., 1995). With this motif one centrosymmetric BB pair and two non-centrosymmetric AC pairs were formed (Fig. 2). Mercury -program (Macrae et al., 2008) also finds some short intermolecular C-H···O, π-π [centroid-centroid distance 3.968 (4) Å] and weak C-H···π contacts (Table 1), which connect these pairs to each other and define the overall structure in the crystal.

Experimental
Bis(trimethylsilyl)amine (HMDS) (526 mg, 3.28 mmol) was dissolved in dry THF under inert atmosphere. 1.6-M n-BuLi (6.15 ml) was added at -10 °C temperature and the resulting solution was placed into dropping funnel and kept under inert atmosphere. (5-Carboxypentyl)triphenylphosphonium bromide (1.5 g, 3.28 mmol) was dissolved in dry THF under inert atmosphere. The solution was cooled to -10 °C and LiHMDS was added dropwise to the reaction flask. After addition the reaction mixture was stirred at room temperature for 20 minutes. Then the reaction mixture was cooled again (ice salt bath) and 1-pyrene carboxaldehyde (755 mg, 3.28 mmol), dissolved in dry THF, was added dropwise into reaction mixture under inert atmosphere. After addition the reaction mixture was stirred at room temperature for 1 h. The reaction was quenched with aq. 5% citric acid, extracted with DCM and obtained extract was evaporated to yield brown oil. Brown plates were crystallized out from this oil within two weeks. These plates were directly used in single-crystal analysis.

Refinement
All H atoms were visible in electron density maps, but those bonded to C were calculated at their idealized positions and allowed to ride on their parent atoms at C-H distances of 0.95 Å (aromatic, olefinic) and 0.99 Å (methylene), with U iso (H) of 1.2 times U eq (C). The O-H protons were found in the electron density map and were fixed in place by DFIX restraint (s = 0.02) at distances of 0.91 Å from N atoms, and U iso (H) values of 1.5 times U eq (O) were used.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.