Redetermined structure of 4,4′-bipyridine–1,4-phenylenediacetic acid (1/1) co-crystal

The asymmetric unit of the title 1:1 co-crystal, C10H8N2·C10H10O4, consists of one half-molecule each of 4,4′-bipyridine and 1,4-phenylenediacetic acid: the complete molecules are generated by crystallographic inversion centres. The dihedral angle between the –CO2H group and the benzene ring in the diacid is 73.02 (7)°. In the crystal, the components are linked by O—H⋯N hydrogen bonds, generating [1-2-1] chains of alternating amine and carboxylic acid molecules. The chains are cross-linked by C—H⋯O interactions. This structure was previously incorrectly described as a (C10H10N2)2+·(C10H8O4)2− molecular salt [Jia et al. (2009 ▸). Acta Cryst. E65, o2490–o2490].

The resulting crystal structures can generate diverse physical and chemical properties such as solubility and stability that differ from the properties of the individual components. Crystal engineering plays an important role in the formation of co-crystals of desired properties so that they can find their applications in pharmaceutical industries (Childs et al., 2009 andWalsh et al., 2003). Herein, we report the supramolecular architecture of 1,4-phenylenediacetic acid and 4,4′-bipyridine co-crystal formed via O-H···N hydrogen bridges and C-H···π interactions.
The title compound can be prepared under hydrothermal condition using a mixture of 1,4-phenylenediacetic acid and 4,4′-bipyridine (1:1) in water. The acetic acid moiety involving C1, C2, O1 and O2 in 1,4-phenylenediacetic acid molecule makes dihedral angles of 73.04 (4)° and 2.06 (1)° with the phenyl and pyridyl ring planes respectively. These values are very close to those reported by Chinnakali et al. (1999). The dihedral angle between phenyl and planar pyridyl rings of 4,4′-bipyridine is found to be 73.21 (4)°. In the crystal lattice, the molecules are linked with one another through O1-H9···N1 hydrogen bonds with O···N distance of 2.637 (1) Å that extends in one direction leading to a supramolecular chain like structure. These zig-zag 1D chains are further connected via C-H···O bridges (C7-H6···O2 and C9 -H7···O2 with C···O distances of 2.50 (1) Å and 2.45 (2) Å respectively) giving rise to a 2D layered structure in the solid state. In graph set notations (Bernstain et al., 1995), such 1D chains can be described as C 2 2 (20) where the subscripts and superscripts are the number of hydrogen bond donors and acceptors respectively. There are certain hydrogen bonded rings of descriptors R 1 2 (7), R 4 4 (16) and R 4 4 (30) which have periodic repetitions throughout the crystal lattice. The adjacent layers are stacked in nearly parallel fashion by means of weak C-H···π interactions (C···π distance = 3.838 Å) between the methylene C-H and phenyl ring-π systems. These weak intermolecular forces together with the strong hydrogen bonds form the overall 3D supramolecular architecture. ?

S3. Refinement
Structure determination work was done using the WinGX platform (Farrugia, 2012). All the hydrogen atoms were located in difference Fourier maps and refined with isotropic atomic displacement parameters. No restraints were applied for any other parameter during structure refinement.

Figure 1
The molecular structure of (I) showing 50% probability displacement ellipsoids.

Figure 2
A view of the O-H···N, C-H···O and C-H···π interactions observed in the crystal structure of the title compound.  (11) 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 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.