1,6-Bis[(2,2′:6′,2′′-terpyridin-4′-yl)oxy]hexane

The molecule of the title compound, C36H32N6O2, lies about an inversion center, located at the mid-point of the central C—C bond of the diether bridge. The terminal pyridine rings form dihedral angles of 4.67 (7) and 26.23 (7)° with the central ring. In the crystal, weak C—H⋯N and C—H⋯O interactions link the molecules into a three-dimensional network.

We wish to thank the Univeristy of Kwazulu-Natal for supporting this research by providing both funding and facilities. The title compound is the second in a series of ligands developed in an effort to harness multifunctional activity.
Coordination of these ligands to platinum(II) should enable covalent binding of DNA through both metal centres, thus increasing the number of adducts formed. Furthermore the presence of the flexible diol derived linkage will provide the complex with the potential to engage in long range interactions with DNA.
The ligand crystallized in the orthorhombic space group Pbca, with a half molecule in the asymmetric unit and Z = 4.
Crystallographically imposed inversion symmetry relates two halves of the ligand. The inversion center is located at the mid-point of the diol linkage. The three pyridine rings adopt a trans, trans conformation. The same configuration is observed in the parent 4′-chloro-2,2′: 6′,2′′-terpyridine (Beves et al., 2006) and is a common feature of uncoordinated terpyridine ligands in general (Akerman et al., 2011;Bessel et al., 1992).
The central pyridine ring of the terpyridine fragment lie in the same plane as the bridging chain. The terminal pyridine rings are, however, canted relative to the central ring. The C7-C6-C5-N1 torsion angle is -25.8 (2)°, while the C9-C10-C11-N3 torsion angle is 4.9 (2)° ( Fig. 1). The large torsion angle formed by one of terminal pyridine groups with the central ring is seemingly to allow for interaction between the pyridine N1 atom and the hydrogen atom H4 of an adjacent molecule, with the distance of 2.65 Å. There are also other short contacts C-H···O and C-H···N, ranging from 2.65 to 2.71 Å. These contacts link the molecules into a herringbone pattern (Figure 2). There is no indication of meaningful π··· π or C-H··· π interactions in the lattice, which are often observed in terpyridine structures (Beves et al. 2006).

Experimental
The title compound was prepared by an adaptation of a previously described method (Van der Schilden, 2006;Constable et al., 2005). Hexanediol (1.13 mmol) was added to a suspension of ground potassium hydroxide (6.69 mmol) in DMSO (30 ml). The solution was heated to reflux for 1 h after which 4′-chloro-2,2′:6′,2′′-terpyridine (2.23 mmol) was added. The mixture was again brought to reflux for an additional 24 h. After cooling to room temperature, the brown mixture was added to cold water (100 ml). The resulting off-white precipitate was filtered, rinsed with cold ethanol and air dried.
Single crystals were grown by slow liquid diffusion of n-hexane into a chloroform solution of the compound.

Refinement
All non-hydrogen atoms were located in the difference Fourier map and refined anisotropically. The positions of all hydrogen atoms were calculated using the riding model with C-H(aromatic) and C-H(methylene) distances of 0.93 Å and U iso = 1.2 U eq . 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1999); software used to prepare material for publication: publCIF (Westrip, 2010).

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level.  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 > σ(F 2 ) is used only for calculating R-factors(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.