4,4′-(o-Phenylenedioxydimethylene)dipyridinium dinitrate

The cation of the salt, C18H18N2O2 2+·2NO3 −, lies about a twofold rotation axis. The pyridinium ring is almost coplanar with the phenylene ring [dihedral angle between rings = 5.69 (9)°]. The crystal structure shows π–π stacking interactions [centroid–centroid distance = 3.70 (1) Å] between the pyridinium rings and the phenylene rings, generating a linear chain structure. The cation also forms two N—H⋯O hydrogen bonds to two nitrate groups.

The cation of the salt, C 18 H 18 N 2 O 2 2+ Á2NO 3 À , lies about a twofold rotation axis. The pyridinium ring is almost coplanar with the phenylene ring [dihedral angle between rings = 5.69 (9) ]. The crystal structure showsstacking interactions [centroid-centroid distance = 3.70 (1) Å ] between the pyridinium rings and the phenylene rings, generating a linear chain structure. The cation also forms two N-HÁ Á ÁO hydrogen bonds to two nitrate groups.

The authors thank the Specialized Research Funds for Technological
Innovative Talent of Harbin (RC2009XK018007) and Heilongjiang University for supporting this study. which reacted with AgNO 3 , Cu(ClO 4 ) 2 and Co(NCS) 2 to produce a helical metallopolymer, a bridged dinuclear complex and a monomeric octahedral complex, respectively. Puddephatt's group have investigated a series of silver complexes of two U-shaped bis(amidopyridyl) ligands, which assemble into macrocyclic and one-dimensional chain that are connected further into two-or three-dimensional structures by anion binding and hydrogen bonding. Our group has report three kinds of flexible pyridyl-based ligands in the previous report (Gao et al. 2006;Gao et al. 2009a;Gao et al. 2009b). As a part of our continuing research for bipyridyl aromatic ligands, we report the crystal structure of the title compound here.

Structure Reports Online
In the title compound, the diprotonated 1,2-bis(4-pyridylmethoxy)benzene cation is centrosymmetric. The two terminal pyridyl rings lie in an almost coplane arrangement with the central benzene ring [dihedral angles of 5.69 (9)°]. The dihedral angle between the two pyridyl rings is 10.22 (8)° ( Figure 1).
In the crystal packing structure, the πi-πi stacking interactions [distance of 3.70 (1) Å] existing between each spacer benzene ring and two adjacent pyridine rings from different ligands link the ligands into a one-dimensional chain structure.
Furthermore, the uncoordinated nitrate anions are stabilized by the C-H···O hydrogen bonds ( Figure 2, Table 1).

Experimental
The 1,2-bis(4-pyridylmethoxy)benzene was synthesized by the reaction of o-benzenediol and 4-chloromethylpyridine hydrochloride under nitrogen atmosphere and alkaline condition (Gao et al., 2004;Gao et al., 2006). Colorless block-shaped crystals of the title compound were obtained by slow evaporation of an ethanol solution after several days.

Refinement
H atoms bound to C atoms were placed in calculated positions and treated as riding on their parent atoms, with C-H = 0.93 Å (aromatic), C-H = 0.97 Å (methylene), and with U iso (H) = 1.2U eq (C). N-bond H atoms were located in a difference Fourier map and were refined freely. 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 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.  (3) 170 (3)