1,4-Bis(2,2′:6′,2′′-terpyridin-4′-yl)benzene

The asymmetric unit of the title compound, C36H24N6, comprises a whole molecule. Supramolecular interactions between neighbouring molecules are essentially π–π stacking interactions with small interplanar distances [3.5140 (15) and 3.6041 (15) Å]. The central phenylene ring is tilted with respect to the two pyridine substituents, subtending angles of 36.17 (11) and 34.95 (11)°. Three of the peripheral pyridine substituents are almost coplanar with the central pyridines [dihedral angles = 5.10 (12)-8.21 (12)°], but one subtends an angle of 24.86 (12)°.


Related literature
For coordination polymers having the title compound as a bridging ligand, see: Jones et al. (2010); Koo et al. (2003). For oligomeric coordination compounds having the title compound as bridging ligand, see: Maekawa et al. (2004); Schmittel et al. (2005Schmittel et al. ( , 2006. For a description of the Cambridge Structural Database, see: Allen (2002). For related work from our research group showing the motivation to use aromatic ligands for the design of photoluminescent materials, see: Girginova et al. (2007); Lima et al. (2006Lima et al. ( , 2009Shi et al. (2008). For absolute structure, see: Flack (1983 however, that only five crystal structures in which this molecule is used as a ligand are known. While some of these compounds correspond to discrete complexes, namely two dinuclear complexes of zinc and iridium (Schmittel et al., 2006;Maekawa et al., 2004) and a tetranuclear complex of zinc (Schmittel et al., 2005), other two correspond to coordination polymers: a one-dimensional polymer of copper and a three-dimensional framework containing copper and molybdenum (Jones et al., 2010;Koo et al., 2003). Following our interest in the design and synthesis of novel lanthanide photoluminescent complexes (Lima et al., 2006;Lima et al., 2009) and coordination polymers (Shi et al., 2008;Girginova et al., 2007), we isolated crystals of the title compound as a by-product of hydrothermal synthesis.
Despite of the various possible molecular symmetry elements, the asymmetric unit comprises one whole molecule of the title compound ( Figure 1). Both terpyridine (terpy) substituents have the three N-atoms in mutual trans conformation.
The central benzene ring forms angles of 36.17 (11) and 34.95 (11)° with the two neighbouring pyridine (py) substituents, which are almost coplanar [angle between rings 1.22 (11)°]. The terminal py rings subtend small angles with each central py: while three of these dihedral angles are in the 5.10 (12)-8.21 (12)° range, the fourth is slightly larger and measured as 24.86 (12)°. The crystal packing ( Figure 2) is mainly driven by the need to effectively fill the available space (van der Waals contacts) in conjunction with a couple of strong π-π stacking interactions. The latter interactions occur between the central py rings and two terminal ones of neighbouring molecular units: distance between centroids of 3.5140 (15) and 3.6041 (15) Å. These interactions (green dashed lines in Figure 2) promote the formation of a two-dimensional supramolecular layer in the ab plane.
A mixture containing pbt (ca 0.4 mmol, 0.2162 g) and Eu 2 O 3 (ca 0.1 mmol, 0.0352 g) in ca 4 ml of distilled water was stirred at ambient temperature for 5 minutes. The suspension was then transferred to a 8 ml teflon-lined stainless reaction vessel. The reaction took place at 180 °C for approximately 48 h. Large yellow crystals of unreacted pbt were directly isolated from the contents of the vessel, and were washed with copious amounts of water and ethanol before drying under vacuum.

Refinement
Hydrogen atoms bound to aromatic carbon atoms were located at their idealized positions and were included in the final structural model in riding-motion approximation with C-H = 0.95 Å. The isotropic thermal displacement parameters for these atoms were fixed at 1.2 times U eq of the respective parent carbon atom.
A total of 3381 estimated Friedel pairs have been merged and were not used as independent data for the structure refinement. Prior to this strategy, the Flack parameter (Flack, 1983) converged to 0.0 (2). Fig. 1. Asymmetric unit of the title compound showing all non-hydrogen atoms represented as thermal ellipsoids drawn at the 80% probability level and hydrogen atoms as small spheres with arbitrary radius. 1,4-Bis(2,2':6',2''-terpyridin-4'-yl)benzene